marine weather of the inland waters of western washington · marine weather of the inland waters of...
TRANSCRIPT
NOAA Technical Memorandum ERL PMEL-44
MARINE WEATHER OF THE INLAND WATERS
OF WESTERN WASHINGTON
James E. OverlandBernard A. Walter, Jr.
Pacific Marine Environmental LaboratorySeattle, WashingtonJanuary 1983
UNITED STATESDEPARTMENT OF COMMERCE
Malcolm Baldrige,Secretary
NATIONAL OCEANIC ANDATMOSPHERIC ADMINISTRATION
John V. Byrne,Administrator
Environmental ResearchLaboratories
George H. LudwigDirector
CONTENTS
Abstract 1
1. Introduction 2
2. Climatological Summary 22.1 Air temperature 22.2 Preci pitation 62.3 Cloud cover and fog 62.4 Wind and waves 122.5 Air qual ity 122.6 Surface hydrology 23
3. Large-scale Meteorological Characteristics 23
4. Regional Meteorological Phenomena 304.1 Overview 304.2 Gap winds and bora 324.3 Orographic low-pressure formation 36
in the lee of the Olympic Mountains4.4 Effects of orography on precipitation--the 46
Puget Sound convergence zone4.5 Diurnal wind variations--the sea breeze 51
and valley breeze
5. Summary 576. Acknowledgements 597. References 60
iii
Figures
Figure 1. Location map for western Washington 3and southwest British Columbia.
Figure 2. Topographic map of northwest Washington. 4Figure 3. Annual temperature cycle at SEATAC 5
Airport (1945-1970).Figure 4. Mean annual precipitation (1930-1957) 8
for western Washington.Figure 5. Annual cycle of precipitation at SEATAC 9
Airport (1945-1970).Figure 6. Annual cycle of clear or partly cloudy 10
days at SEATAC Airport (1945-1980).Figure 7. January and July surface wind roses for 14
western Washington.Figure 8a. One-year time series of the N-S wind 17
component for West Point.Figure 8b. Frequency spectra for the north and east 18
components of wind for West Point during winter.Figure 8c. Frequency spectra for the north and east 19
components of wind for West Point during summer.Figure 9. Annual wave climatology computed for West 20
Point from the wind climatology at SEATAC Airport.Figure 10. Mean annual particulate concentration 22
for 1980.Figure 11. Mean annual runoff (m3 s-l) for Puget Sound. 24Figure 12a. Mean annual cycle of discharge for 25
Puget Sound's three major tributaries.Figure 12b. Interannual variability of discharge 26
for Puget Sound's three major tributaries.Figure 13. Typical weather patterns (LIt L2 t HIt H2) 27
affecting the Pacific Northwest.Figure 14. Typical local wind patterns for the 31
passage of a front through western Washington.Figure 15a. Sea-level pressure analysis for 00 GMT 33
24 February 1980 for western Washington.Figure 15b. Local wind field on 23 February and sea- 33
level pressure analysis for 21 GMT 23 February 1980for the Straits of Juan de Fuca and Georgia.
Figure 16a. Sea-level pressure analysis for 00 GMT 3414 February 1980.
iv
Figure 16. (b) Local wind field on 13 February 1980 34and sea-level pressure analysis for 21 GMT13 February 1980.
Figure 16. (c) Wind and dewpoint fields from surface 35and aircraft reports 21-24 GMT 13 February 1980.(Overland and Walter, 1981).
Figure 17. Surface map, 12 GMT 28 November 1979. 37Figure 18. Cross section of potential temperature 38
(KO) across the state of Washington.Figure 19. Regional surface map for 12 GMT, 40
13 February 1979.Figure 20. (a) Sea-level pressure analysis at 41
00 GMT 19 February 1980, and (b) mesoscale windand pressure field at 21 GMT 18 February 1980.
Figure 20. (c) Sea-level pressure analysis at 4200 GMT 29 February 1980 and (d) mesoscale windand pressure field at 21 GMT 28 February 1980.
Figure 20. (e) Sea-level pressure analysis at 4300 GMT 10 March 1980 and (f) mesoscale windand pressure at 21 GMT 9 March 1980.
Figure 21a. Plumes from upwind stacks at various 44elevations (after Hunt and Snyder, 1980).
Figure 21b. Comparison of experimental and analytically 45computed streak-lines in the horizontal plane atmid-level of a Gaussian-shaped obstacle for a Froudenumber of 0.154 (after Riley et al., 1976).
Figure 22. Sum of the perturbation pressure field from 47Smith's hydrostatic linear model and a hypo-thetical synoptic pressure field (Smith, 1981).
Figure 23. Polar representation of the wind speed and 49direction at Hoquiam, Washington, during tenconvergence zone events (after Mass, 1981).
Figure 24. Streamlines over the Puget Sound area during 50the convergence zone event of May 2-3, 1978.
Figure 25. Schematic view of the low-level flow during 52a convergence event (Mass, 1981).
Figure 26. (a) Summary of the number of times the lowest 53cloud deck in Puget Sound occurred in each compos-ite zone during five convergence zone events.(b) Temperature deviations (OF) from the Puget Soundmean for each composite zone. (c) Summary of thenumber of precipitation events that occurred in eachcomposite zone during ten convergence zone events(after Mass, 1981).
Figure 27. Annual variation of precipitation for the 54rain shadow and northern, central, and southernPuget Sound regions (Mass, 1981).
v
Figure 28. Percentage contributions to total precipi- 55tation at three coastal stations and three inlandstations from warm sector, narrow cold-frontal, widecold-frontal, and post-frontal rainbands on8 December 1976.
Figure 29. Resultant wind hodographs for stations 56in the Strait of Juan de Fuca, north, central,and south Puget Sound for July 1950.
Figure 30. Average sea-level pressures at each hour 58of the day for July 1950 at Tatoosh Island, PortAngeles, Everett, Bellingham, and sea-level pressuredifferences between Port Angeles and Bellingham,Port Angeles and Everett, and Tatoosh Islandand Port Angeles.
vi
Tables
Table 1. Probability of freezing temperatures for 7three stations in the Puget Sound region.
Table 2. Average total hours of sunshine and mean 11daily total solar radiation for SEATAC Airport(1966-1975).
Table 3. Percentage frequency of occurrence of fog 13for all observations by month.
Table 4. Monthly wind speed/direction frequencies 15(1949-1958).
Table 5. Annual average concentration of suspended 21particulates for stations in the Puget Soundregion (1972-1979).
Table 6. Number of days per month with synoptic 29weather patterns Ll, L2, HI, H2.
Table 7. Comparison of winds reported by Reed (1980) 48in Hood Canal 14-15 GMT 13 February 1979 andthose calculated from Eq. 1.
vii
Marine Weather of the Inland Waters of Western Washington l
James E. Overland and Bernard A. Walter, Jr.
ABSTRACT. The mid~latitude, west coast marine climate of westernWashington is typified in summer by high sea-level pressure as partof the North Pacific weather pattern and in winter by a sequence ofstorms which originate to the west. Mean and extreme temperaturesare moderated by the proximity of the Pacific Ocean and Puget Sound,resulting in an mean temperature of 4°C in January and 17°C inAugust at Seattle.
Local variations in precipitation and wind are influenced byboth large-scale weather patterns and the region's topography. Fiftypercent of the annual precipitation for most of the inland region fallsin the four months from November through February, and less than fivepercent falls in July and August; the driest region is to the northeastof the Olympic Mountains. Over the inland waters, the winds flow fromhigh to low sea-level pressure in the direction of the local channels.
Recent studies by the University of Washington and PMEL on thePuget Sound convergence zone, sea and valley breeze, precipitationpatterns and local wind patterns are summarized. The storm whichresulted in destruction of the Hood Canal Bridge has shown that thepresence of the Olympic Mountains can induce a regional low-pressuresystem in their lee which can result in strong surface winds overthe inland waters.
lContribution number 595 from the NOAA/ERL Pacific Marine EnvironmentalLaboratory, 3711 15th Avenue N.E., Seattle, Washington 98105.
1
1. Introduction
The climate of the Puget Sound Basin in western Washington State is amid-latitude, west coast marine type. The source regions of the predominantair masses reaching Puget Sound are over the Pacific Ocean; this produces amoderating influence on the weather in both summer and winter. A prevailingwesterly-to-northwesterly flow of air associated with high sea-level pressurein the eastern Pacific results in a dry season beginning in June and reachinga peak in midsummer. l In the late fall and winter the high-pressure arearetreats to the south allowing a series of storms to cross the region, thuseffecting a wet season that begins in October, reaches a peak in winter, anddecreases in the spring. This winter pattern is occasionally interrupted bythe influence of continental high pressure which is accompanied by cold temperatures and dry air.
Topography has a large influence on the weather of Puget Sound (Figs. 1and 2). The region is flanked on the west by the Olympic Mountains and on theeast by the Cascade Range. The elevation of the region varies from sea levelon the Sound to 2500 mand higher in the mountains. The Cascades and theCanadian Rocky Mountains shield Puget Sound from cold air masses moving southward across Canada. To the west, the Willapa Hills (which lie south of Hoquiam,Washington), the Olympic Mountains, and the Coastal Range on Vancouver Islandare effective in protecting the area from more intense winter storms thatreach the coast by forcing orographic precipitation on the western slopes(Hobbs et al., 1975). The Strait of Juan de Fuca, the Strait of Georgia, andthe Chehalis River Valley provide low-level passages for maritime air to moveinland and are the primary determinant of surface winds.
The next section provides a climatological overview of air temperature,precipitation, winds, and other important climatological variables for thePuget Sound Basin. Section 3 discusses the synoptic or large-scale distribution and propagation of high and low sea-level pressure patterns that influencethe meteorology of western Washington. Section 4 provides a summary of anumber of regional meteorological phenomena that contribute to the climatologyof the region.
2. Climatological Summary
2.1. Air temperature
The yearly cycle and variability of monthly mean temperatures measured atSEATAC Airport, 20 miles south of Seattle, are shown in Fig. 3. During the
lThe meteorological convention of specifying the direction from which thewind is blowing is used throughout this memorandum.
2
49
48
47N
VANCOUVERISLAND
PACIFICOCEAN
? 2,5 5.0 7,5 Iqo
KILOMETERS
BRITISH COLUMBIA
Mt. Baker
n»enn»ofTl
~ocZ----1»Zen
Figure 1. Location map for western Washingtonand southwest British Columbia.
3
~ 0-300 meters
M;!{:i.Vl 300-1500 meters
o 30 60km
Figure 2. Topographic map of northwest Washington.
4
25
20-uo---W0:: 15:::>
~0::W
~ 10wr-
5
MONTHLY TEMPERATURENORMALS AT SEATAC
JFMAMJJASOND
--- AVERAGE MAXIMUM
---- MEAN
-------- AVERAGE MINIMUM
Figure 3. Annual temperature cycle at SEATAC (National ClimaticCenter, 1980). Values are the official normals (1945-1970).
5
summer months, afternoon temperatures at lower elevations are often 20°C to25°C. Maximum temperatures reach 29°C to 32°C on a few days during a givenyear; temperatures of 38°C or higher occur infrequently. In winter, temperatures in the Puget Sound lowlands usually range from 3°C to 7°C in the afternoon and from -2°C to 5°C at night. Almost every winter the temperature dropsto between -7°C and -12°C on a few nights, with the coldest weather occurringduring a few short outbreaks of cold, dry air from the north or the east.
The longest growing season, 190 to 220 days, occurs on the San JuanIslands and in areas nearest to Puget Sound. Variations of several weeks inthe duration of the growing season can occur within short distances. Near thewater, the average date of the last OoC temperature in the spring is mid-April,and the average date of the first OoC temperature in the fall is near the endof October (Table 1). Temperatures of -2.2°C or lower are usually recorded 15to 30 days later (Phillips, 1968).
2.2. Precipitation
The moist maritime air that reaches the Washington coast in late fall andwinter is approximately the same temperature as the surface waters. Thus,orographic lifting and cooling of these air masses moving inland readilyresult in widespread cloudiness and precipitation. The mean annual precipitation chart for western Washington illustrates the extreme horizontal variation in precipitation (Fig. 4). The driest sections of the Sound are to thenortheast of the Olympic Mountains and receive 45 to 75 cm of precipitationannually. Over most of the lowlands, annual precipitation ranges from 100to 130 cm, increasing to 190 cm in the foothills and from 380 to 510 cm on thewettest slopes of the mountains. Due to the mild weather of the Puget SoundBasin, most of the precipitation below 500 m is in the form of rain. Theyearly cycle of rainfall measured at SEATAC Airport indicates that a largevariability of rainfall can be expected in any given month (Fig. 5). Fiftypercent of the annual precipitation for most of the inland region falls in thefour-month period from November through February. The combined rainfall forthe months of July and August is less than five percent of the annual total.
Since 1900 there has been a decrease and then an increase in the 10ngterm trend of precipitation. The ten-year mean rainfall for 1901-1910 atSeattle was 87 cm; the mean then decreased to 70 cm for 1921-1930, and hasincreased to 93 cm for the period 1961-1970 (Church, 1974).
Total snowfall in the Puget Sound lowlands is generally less than 25 cmper year and normally occurs from November to March, with maximum amounts inJanuary.
2.3. Cloud cover and fog
The P~get Sound climate is characterized by a high percentage of overcastdays (Fig. 6). The number of clear or partly cloudy days each month rangesfrom 5 to 7 in the winter, 8 to 14 in the spring and fall, and 17 or more inthe summer. Table 2 gives the average total hours of sunshine and mean dailytotal solar radiation (in calories cm-2), by month for SEATAC.
6
Table 1.--Probability of freezing temperatures forthree stations in the Puget Sound region*
(at 0°, -2.2°, -4.4°C)
Spring Months Fall Months
Station Temp. 90% 50% 10% 10% 50% 90%
Bothell OoC Apr 18 May 13 June 7 Sept 12 Oct 5 Oct 28
(1931- -2.2 Mar 19 Apr 13 May 8 Oct 7 Oct 30 Nov 221952)
-4.4 Feb 7 Mar 8 Apr 2 Oct 22 Nov 15
SEATAC OoC Mar 15 Apr 9 May 4 Oct 10 Nov 2 Nov 25
(1945- -2.2 Feb 5 Mar 9 Apr 4 Oct 26 Nov 17 Dec 161960)
-4.4 Feb 9 Mar 9 Nov 20
University OoC Feb 26 Mar 23 Apr 17 Oct 26 Nov 18 Dec 11
of -2.2 Feb 2 Mar 2 Nov 21 Dec 18
Washington -4.4 Jan 17 Feb 19 Dec 3
(1931-1960)
*After Phillips, 1968.
7
MEAN ANNUAL PRECIPITATION, 1930-1957WESTERN WASHINGTON STATE
I1240
Figure 4. Mean annual precipitation (1930-1957) for western Washington.Contours are in inches (1 in =2.54 cm). (From Philipps, 1968.)
8
35 MONTHLY PRECIPITATIONAT SEATAC
30 \ /\ /\ /
25 \ /\ ,/
./,.-..
"'" /E " /u 20 \'"-'" /z \ /0- \ /~r- 15 \ J0.. /- \u Iw
\'/""0:: /0.. 10 \ /\\ /J
5,-'/ ,
,- "'-0
............ _-- .............---J F M A M J J A S 0 N 0
---- GREATEST MONTHLY
--- MEAN
-------- LEAST MONTHLY
Figure 5. Annual cycle of precipitation at SEATAC (National ClimaticCenter, 1980). The mean is the official normal (1945-1970) and theextremes are for the period of record (1945-1980).
9
25
20
15
NUMBER OF CLEAR ORPARTLY CLOUDY DAYS ATSEATAC PER MONTH
J F M A M J J A SON D
I I CLEAR DAYS OR PARTLY CLOUDY
V/lJl//IM CLEAR
Figure 6. Annual cycle of clear or partly cloudy days (1945-1980) atSEATAC (National Climatic Center, 1980).
10
Table 2.--Average total hours of sunshine and mean daily total solarradiation for SEATAC Airport 1966-1975* (in Langleys, by month)
J F M A M J J A S o N o
Hours ofsunshine
61 122 180 208 274 257 318 287 230 140 75 45
Total solar 80 162 266 390 513 531 581 478 353 203radiation
*After Critchfield, 1978.
11
98 62
· Frequently during the summer and fall, fog or low clouds, 300 to 600 mthick, form over Puget Sound and the lowlands during the night and dissipateby afternoon (Table 3). In the fall, there is a high incidence of fog becauseof radiational cooling at night. In the summer, cool, moist coastal air isadvected into the Strait of Juan de Fuca and northern Puget Sound resulting infog formation.
2.4. Wind and wavesPuget Sound wind patterns are influenced by mountain barriers and low
level passages (Fig. 7). In southern Puget Sound the strongest winds comefrom the south to southwest when the more intense Pacific storms move inland.During winter, the occasional presence of high pressure over the interior ofBritish Columbia can produce strong easterly winds blowing down pressuregradient through the Strait of Juan de Fuca (Reed, 1931). In summer, windsare generally light in the afternoons; a northerly sea breeze develops overPuget Sound and the lowlands, and a westerly sea breeze develops in the Straitof Juan de Fuca. Over the Main Basin of Puget Sound, extremes in wind speed canbe expected to exceed 25 ms-l once in 2 years, 40 ms-l once in 50 years, and45 ms-l once in 100 years (Phillips, 1968). The wind statistics for SEATACare given in Table 4; wind statistics for other stations, including Bellingham,Everett, and Olympia, are given in the Climatological Handbook, Columbia RiverBasin States (1968). A study of regional wind patterns for western Washingtonand southern British Columbia is given by Schoenberg (1983).
The time series of the N-S wind component and energy spectra derived froma one-year record (1975-1976) of winds at West Point, a representative locationfor the Puget Sound Main Basin, are shown in Fig. 8a (Cannon and Laird, 1978).The energy spectrum of both the N-S and E-W wind components for winter (Fig. 8b)shows peaks at 0.25 cycles day-1 (i.e., frequency of storm passage), and thespectrum for summer (Fig. 8c) has a diurnal peak in the E-W component indicatingthe dominant sea breeze/valley breeze influence between the Sound and theadjacent lowlands to the east.
The height and dominant period of wind-waves are a function of windspeed,wind duration, and fetch. An annual wave climatology for West Point (fig. 9)was calculated from windspeed and duration from SEATAC and fetches for PugetSound (Skjelbreia, 1981) using relations from the Shore Protection Manual(1973). The largest waves come from the south along the major axis of theSound during storm events. In addition, a large frequency of intermediateheight waves come from the southwest; in this case wave heights are fetchlimited during the strong post-frontal southwesterly winds.
2.5. Air qualityIn general, air quality problems are less serious in the Puget Sound
region than in other major metropolitan regions because of the proximity ofthe ocean and the tendency for considerable advection north and south throughPuget Sound. However, pollutants accumulate during periods of stagnation whenlight winds or stable stratification prevail. Since 1965, the Puget Sound AirPollution Control Agency has operated a network of monitoring stations throughout the Puget Sound region to measure suspended particulates and concentrationsof S02' CO, and 03.
12
Tab
le3.
--P
erce
ntag
efr
eque
ncy
ofoc
curr
ence
offo
gfo
ral
lob
serv
atio
nsby
mon
th*
JF
MA
MJ
JA
So
ND
Ann
Bel
lingh
am8.
45.
93.
21.
31.
72.
12.
44.
510
.017
.410
.75.
16.
0
Hoq
uiam
20.2
19.7
12.6
10.0
4.9
7.5
8.5
11.9
14.9
19.5
28.6
26.8
15.2
Pt.
Ang
eles
1.9
5.1
1.7
0.9
2.8
6.7
11.8
15.2
16.3
15.6
6.1
5.1
7.5
......
wE
vere
tt21
.820
.712
.17.
77.
012
.511
.715
.620
.829
.628
.223
.817
.6
Oly
mpi
a23
.523
.214
.78.
44.
14.
86.
09.
917
.928
.830
.425
.816
.4
Sea
Boe
ing
13.7
11.3
6.1
3.7
1.9
2.7
3.2
4.9
12.1
17.5
20.7
14.5
9.3
SEAT
AC13
.712
.56.
74.
43.
14.
66.
97.
814
.820
.321
.214
.510
.9
Whi
dbey
5.6
8.7
4.0
2.6
2.5
4.5
8.4
10.3
14.1
20.7
15.9
6.6
8.7
Tat
oosh
7.9
9.2
5.7
6.1
8.1
14.6
22.8
23.7
19.7
10.6
7.6
9.9
12.2
*Fr
omth
eC
lim
atol
ogic
alH
andb
ook
t19
68.
Mos
tst
atio
ns
repr
esen
tre
cord
sfo
r19
49-1
958.
#'
~IO
-NO
RT
HD
ALL
ES
(I)
"":':.
',.
.J~.
II-E
VE
RE
TT
(2)
~l(E
~) "-----*
41
-NO
RT
Ht"
BE
ND
(I)
'43
-TA
CO
MA
(2)
.,.. ~3
2-
CH
EH
ALI
S(I
)
.3
7-C
AS
TL
ER
OC
K(I
)
.24
-KE
LS
O(2
)4
-N
OR
THH
EA
D(I
)
46
-NO
RT
HD
ALL
ES
(I)
*-
'~Sl::ATTLE'(I)
.~33-NORTH
"B
EN
D(I
)
56
-TA
CO
MA
(2)
*,2
2-C
HE
HA
LIS
(I)
'.!2~C
AS
TLE
RO
CK
(I)
24
-KE
LS
O(2
)
.......
4=>0
JANU
ARY
JULY
SP
EE
DS
YM
BO
L
-- ®
IND
EX
CLA
SS
IND
EX
CLA
SS
III4
-15
12 14
-12
I16
-31
213
-31
I3
2-4
72
32
-46
I4
8+
24
7+
AL
LS
TA
TIO
NS
HA
VE
TH
ES
AM
ER
AN
GE
(0-3
MP
H)
SC
ALE
INP
ER
CE
NT
OF
TIM
E
II
1--.
o25
50
75
Figu
re7.
Janu
ary
and
July
surf
ace
win
dro
ses
for
wes
tern
Was
hing
ton
(aft
erP
hil
lip
s,19
68).
Thi
sfi
gure
mus
tbe
inte
rpre
ted
with
som
eca
reas
stro
nges
tw
inds
atea
chst
atio
ndo
not
nece
ssar
ily
occu
rdu
ring
the
sam
esy
nopt
icev
ent.
Table 4.--Monthly wind speed/direction frequencies*(1949-1958) for SEATAC
JAN U A R • F E B R U A R •
HCURLY CaSERYAT 10~S OF .I~O SPEEO HOURLY CBSERYATlO~S OF .I~O SPEEO"IUS PER HOUR "ILES PER HOUR
1 • 8 13 19 25 32 39 1 • 8 13 19 25 32 39Ie TO TO TO TC TO TO TO OYER AYE TO TO TO TO TO TO TO TO OyeR AYE
lolR 3 1 12 18 2. 31 38 'b .b TOUL SPEEO OIR 3 1 12 18 2' 31 38 'b .b TOUL SPEEO
.. J .b ';.9 2.5 1.5 0.5 ).1 b.O 11.0 ~ 0.' 0.9 2.0 1.5 0.3 0.1 5.2 11.2NNe J.3 1.) l.8 2.1 ".3 • b.5 11.2 ~He 0.' 1.1 2.9 1.1 0.2 b.3 10.b~E J.l 1.1 2.2 J.l • 5 •• 8.2 HE 0.5 I.' 1.9 O.b • •• 5 B.5E~E :i.l\ J .1 C.b J.l 1.1 1.0 E~E 0.3 0.1 0.1 001 I.B 1.0E 1.1 2.J 2.2 O.B 0.1 bol 8.0 E 0.1 I •• 1.1 O.b •• 3 1.8ESE 1. ) 3.·"" •• 9 1.2 0.1 1001 B.b nE O.b 2. B 2.9 1.0 0.1 1.5 8.5~E 1.3 3.1 '.b 1.0 • 10.1 1.9 SE O.b 2.1 303 0.5 • 1.2 1.9HE 0 •• 1.B 2.b ).b 0.1 5.b B.l SSE 0.3 2.0 2.2 O.b 0.1 • 5.' B.lS ';.3 1.5 3.1 3.e 0.9 0.2 9.b 12.2 S 0 •• 1.1 3.5 2.9 0.1 0.2 9.3 11.bSS. J .2 J.B 3.1 5.' 2.2 0 •• '.1 12.B 1'.1 SS. 0 •• 1.1 3.1 b.l 2.B O.b 0.1 1•• 9 1'.8S. 0.3 J.l 2.3 •• 1 2.b 0.1 • 10.B 15.6 S. 0.3 0.9 2.B '.b 3.3 0.1 12.1 15.5.S. J.2 J.' J.l O.b 0.3 J.2 • 2.3 13.2 .S. 0.3 0.1 O.B 1.0 O.b 0.3 3.5 13.3
• 0.1 ~.3 ·J.2 • · • 0.1 1.5 • 0.2 0.' 0.5 0.1 0.1 · 1.3 B.5.". j .2 J.I Jol · a•• 5.8 .~. 0.2 0.5 0.2 . • 0.9 b.O~. J.I ".2 Jol · 0.5 101 ~. 0.2 O.b 0.3 . • 1.2 b.lif",.. ~.3 .,;,.It ::'.4 ·).3 J.1 1.5 9.b ~~. 0.1 0.1 1.0 0.' 0.1 2 •• 10.1CUll 9.3 9.3 CALM 11.b 11.bTOTAL 1b .b 19•• 33.5 21.b 1.3 1.b 0.1 100.0 9.9 TOUL 11.' 19.b 30.b 22.0 8.' 1.9 0.1 100.0 10.0
)II IRe ~ APR I L
HOURL. CBSERYAT ICHS OF •• "0 sp~eo HOU~LY OBSERYATlO~S OF .I~O SPEEO~ILES PEA HOUR MILES PER HCUR
1 • 8 13 19 25 32 39 1 • B \3 19 25 32 39T~ TO TO TO TO Til TO TO OYER AYE TO TO TO TO TO 10 10 TO OYER AYE
UlK 3 1 12 18 2' 31 3B .b 'b TOTAL SPEEe OIR 3 1 12 18 2' 31 38 'b .b TOTAL SPEEO
N 0.2 J.B 2.2 1.1 ".2 5.1 11.1 ~ 0 •• 1.1 3.1 2.1 0.3 0.1 b.9 n.9~~E J •• 1.J 2.1 1.5 0.2 5.B 10.2 ~~E 0.2 1.2 3.3 2.0 0.3 1.0 11.0~E J .b 1.2 2.J ).7 · '.5 8.5 ~E 0.5 1.B 2.B 1.2 0.1 b•• 9.1ElfE 0.3 ~.B 0.9 J.2 · 2.2 1.9 E~E 0.3 O.B 1.0 0.2 · 2.3 1.9E O.B 1.5 1•• J.8 .J .1 '.b B.5 E 0.5 1.0 1.0 0.3 • 2.8 1.5E~E J •• 2.3 3.2 1.0 0.1 1.5 B.5 ESE 0.3 I.B 1.1 0.3 0.1 3.5 1.bSE ':;.8 2.9 2.b J.5 · b.B 1.b SE J.l 2.3 2.2 0 •• '.5 1••S~E J.5 1.1 2.·; '.6 ~.I •• B B.b SSE 0.3 1.b 1.9 0.5 0.1 • •• 3 B.B5 J.5 1.8 3.2 2.1 0 •• : .1 B.1 10.1 S ) .. 1.b 2.b 1.8 0.3 0.1 b.9 10.655. ).3 I •• •• 5 5 •• 1.B ) .2 13.1 13 •• 55. J.3 I.' 3.9 3.1 0.9 0.1 10.3 12.2s. J .3 1.1 •• 0 5.b 3.8 c•• 15.1 15.3 S. 0.3 I.' ••• 5.9 3.2 0.5 16.0 I','.. ~ .. J .1 0 •• 1.5 1.1 C., :" .2 5.5 13.5 "5" 0.3 1.3 2.3 2.2 0.8 0.1 b.9 12.'.. 0.1 J.b 0.8 Col 0.1 · 1.9 '.8 • 0.5 0.9 1.3 C.b 0.1 · 3•• 9.0wNW 0.3 J.B J.b · 1.1 b.5 ..~ .. 0.3 0.8 0.9 0.2 2.2 1.8~ .. 0.3 J.b 0.1 ).1 l.b 1.3 ~. 0.3 0.9 1.3 0.3 2.9 a.b~~. :J.2 J.b C•• ~.7 0.1 2.5 10.1 ~H.. 0.3 o.a 1.2 I.' 0.1 3.8 10.9CAL" 8.0 B.O CAL" a.8 a.8TOUL 1'.5 1'.8 33.1 23.1 1 •• 1.5 ~ .1 100.0 10.2 TOTAL l'.b 20.b 3'.2 23.1 b•• 1.1 0.1 100.0 9.B
~ A • J U ~
HlJURL. 08SERYA T10~S OF .. I~O SPEEU HOURL. OBSERY AT I O~S OF "INO SPEED"ILES PER HUUR MILES PER HOUR
I • 8 13 19 25 32 39 1 • a 13 19 25 32 39TO TO TO TO TO TO TO TO OYER AYE TO TO TO TO TO TO TO TO OYER AYE
OIR 3 1 12 18 2. 31 38 4b 4b TOTAL SPEED OIR 3 1 12 1B 24 31 3B 4b 4b TOUL SPEED
N , .4 1.3 '.b 2.1 0.1 9.1 10.b ~ 0.3 1.3 3.5 2.0 0.2 1.2 10.bNNE 0.3 1.5 3.B 1.9 0.1 1.b 10.3 NNE 0.3 I.' 3.2 1.b 0.1 b.l 10.1HE v •• 1.1 3.9 1.9 0.1 8.0 9.9 ~E 0.2 1.3 2.9 1.2 0.1 5.b 9.1ENE ~.2 ".1 ;.9 0.2 2.0 8.1 E~E 0.2 0.5 0.1 0.1 1.b 1.1E 10.5 J.B 0.1 0.1 2.1 b.5 E 0.3 O.b O.b 0.1 1.5 1.1ESE 0.' 1.1 0.9 ).1 2.b 1.0 nE 0.' O.B 0.' 0.1 1. B b.2SE u.1t 1.8 1.2 0.1 3.1 b.' SE 0.3 1.1 1.1 0.1 2.1 1.2SSE 0.2 1.1 1.2 0.1 3.3 1.3 SSE 0.3 1.0 1.2 0.1 2.5 1.5S e.3 1.9 3.0 0.5 • 5.1 B.5 S 0.' 2.1 303 0.9 • b.l B.lSS. 0.' 2.' ••• 2.3 0.2 9.a 10.0 SS. 0.5 2.3 5.8 3.0 J •• • 11.9 10.bsli 0.3 2.1 b.' 5.5 1.1 0.1 lb. 1 12.' S.. 0 •• 2.9 8.B b.9 1.3 0.2 20.' 11.a"5.. 0.2 1.5 3.J 1.9 0 •• • 6.9 10.9 .S.. 0.3 1.9 3.b 1.8 0.2 1.9 10.1.. v.3 1.1 1.9 0.5 0.1 · 3.9 9.2 • 0.3 1.b 2.3 O.b · '.a a.l..... 0.2 1.2 1.3 0.2 2.9 1.9 ..... 0.3 1.3 1.b C.2 3.5 1.1... 0.2 1.3 2.0 0 •• • •• 0 B.5 ".. 0.3 0.9 1.5 0 •• 3.1 B.5H". 0.2 I... 2.2 1.b 0.1 5.1 10.5 H~. 0.2 1.0 1.1 0.8 0.1 3.1 9.9CALM 1 •• 1.b CALM 8•• B••TUTAL 12.1 23.1 .1.2 20.0 2.B 0.2 100.0 9.2 TOTAL 13.' 21.9 '2.1 20.0 2 •• 0.2 100.0 9.1
From the Climatological Handbook, 1968.
15
Table 4.--cont.
J U l Y AUG U 5 T
HOURLY o~~~RVAT IONS OF wIND SPEEU HUURlY 08SERVATIONS UF WINO SPEEDMileS P':A HQUR NILES PER HOUR
1 ~ 8 13 U 25 32 39 1 ~ 8 13 19 25 32 3910 TO TO TO TO TO TO TO OVeR AVE TO TU TO TO TO TO TO TO OVER AVE
olA 3 7 12 18 2~ 31 38 ~6 ~6 TUTAl SPEED olR 3 7 12 18 H 31 38 ~6 ~6 ToUl SPEED
N J.~ 1.7 ~.5 2.2 0.1 8.9 13.1 II O.~ 1.~ ~.7 1.~ 7.9 9.6NNE 0.3 1.9 5.0 1.9 0.1 9.1 10.0 NNE 0.5 1.7 ~.2 1.6 • 8.1 9.5NE ~.4 1.9 3.8 1.7 0.1 7.9 9.6 NE 0.7 1.8 3.~ 1.0 • 7.0 8.8ENr u.3 J.8 0.9 ,).2 • 2.3 7.9 E..E 0.3 0.7 0.8 0.1 1.9 7.3i a;,.3 ; ... e.1 • 1.0 5.~ E o.~ 0.9 0.3 1.7 5.3ESE C.2 J.5 0.3 1.0 5.7 ESE O.~ 0.7 O.~ • 1.6 5.9~E J.3 J.8 ~.8 • 2.0 6.6 SE '.5 1.5 1.0 • 3.0 6.5SSE 0.2 0.9 1.1 • 2.2 7.2 SSE 0.3 1.7 1.1 • 3.1 6.7S c .4 1.7 2.7 0.5 • 5.3 8.2 S 0.8 2.2 2.9 0.3 • 6.3 7.5S~W ,.~ 2.2 Sol 1.3 C.2 9.3 9.2 SSw '.7 2.6 ~.7 1.5 0.1 9.5 9.0~w J.7 3.3 8.0 3.5 ~.4 16.0 1C.1 SW ,).8 2.8 6.2 2.9 0.3 • 13.0 10.0wSW :: ... 1.9 3.3 1.1 0.1 6.7 9.1 wSw '.5 1.9 3.3 1.0 0.1 • 6.7 8.9W ~.~ 1.9 2.6 V... 0.1 5.~ 8.5 W 0.5 1.8 2.2 ,.~ • ~.8 7.9WNW " .2 1.6 1.8 o.~ ~.O 8.2 WNW O.~ 1.5 2.1 0.3 • ~.2 8.0..W 0.3 1.~ 2.1 C.7 ~.5 8.7 N. 0.5 1.5 2.3 0.6 ~.9 8.~
..NW ) .2 1.2 2.8 1.~ 5.6 10.2 ..NW O.~ 1.0 3.0 1.0 5.5 9.5tUN 8.e 8.8 tAlN 11.0 11.0ToUl ".3 H.3 44.9 15.6 1.J l.JC.O 8.~ ToUl 19.0 25.7 ~2.5 12.1 0.6 100.0 7.7
5 E P 7 ~ ~ 8 E R OtT 0 8 E R
HOURLY o8SERVATI0.. s OF WI ..o SPEED HOURLY 08 SERV AT I O"S OF WI ..o SPEEDIIILES PER HOUR NILES PER HOUR
1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 15 32 39TU TU TO TO TO TO TO TO OVER AYE TO TO TO TO TO TO TO TO OVER AVE
UIR 3 7 12 18 2~ 31 38 ~ .. ~6 TOUL SPEEO aiR 3 7 12 18 H 31 38 ~6 ~6 TOUl SPEED
.. J.7 1.8 S.:' 3.1 J.3 11.0 10.5 N 0.5 2.0 ~.~ 1.3 • 8.3 9.3NNe '.7 1.9 5.0 2.7 0.2 10.5 10.2 "NE O.~ 2.~ ~.5 2.3 0.3 9.8 10.2NE , .7 2.3 3.9 1.~ 0.1 8.~ 9.0 NE 0.6 2.2 2.5 0.9 0.1 6.~ 8.5ENE ~ .3 J.6 0.6 J.1 1.6 6.8 ENE 0.3 0.7 0.6 0.1 • 1.8 7.1E 0.5 1.3 :;.5 • 2.3 5.8 E 0.7 1.2 1.2 O.~ 0.1 3.5 7.9ESE '.5 1.2 1.0 • 2.8 6.6 ESE 0.8 1.9 2.5 0.7 0.1 6.0 8.0SE 0.8 1.9 2.J ~.2 ~.8 7.1 SE 0.6 2.5 3.9 0.7 • 7.7 8.3S)E 0.7 1.5 1.~ '.1 • 3.7 6.8 SSE o.~ 1.7 2.~ 0.7 0.1 5.2 8.7) .1.6 1.8 3.3 0.8 0.1 6.6 8.8 5 0.5 2.2 3.8 2.8 0.8 0.1 10.3 11.1SSW ~.~ 1.9 ~.6 2.2 ';'.3 9.5 10.~ SSW O.~ 1.~ ~.1 3.7 1.~ Ool 11.3 12.9SW u.b 2.2 ~.~ 2.7 0.6 J.1 10.6 10.6 SW 0.2 1.0 2.6 3.3 1.3 0.2 8.6 13.3WSw 0.5 1.J 1.~ ':.6 0.1 • 3.7 9.0 WSW 0.1 0.7 1.1 0.6 0.3 • 2.7 11.1W 0.1 1.2 1.2 J.3 • 2.9 7.7 W 0.3 0.5 0.6 Col • 1.5 7.6WNW o.~ 1.2 0.8 '.1 2.5 6.6 WNW '.2 0.7 0.6 • 1.6 6.8NW 0.1 l.~ 1.' -:'.2 2.5 7.' NW 0.3 0.7 0.7 0.1 • 1.8 7.3NNW .1.3 I.e 2.1 1.1 0.1 ~.6 9.9 NNW 0.2 0.7 1.2 o.~ 0.1 2.6 9.1tAlII 11.9 11.9 tAlII 10.9 10.9TOUl 20.1 23 ... 3~.' 15.5 1.8 0.2 100.0 8.1 TOUl ll.~ 22.5 36.7 18.2 ~.7 0.6 100.0 8.9
~ a V E ~ 8 E A OEtEM8ER
Hl;UAlY C8SEAVAT ICNS OF W'''O SPEEO HoUAl Y 08SERVATTONS CF WI"O SPEEO~ILES PEA ~UUA MILES PER ~DUR
1 ~ 8 13 19 25 32 39 1 ~ 8 13 19 25 32 39TO TU 10 TO TO TO TO TO UVEA AVE 10 TO TO TO TO TO TO TO DVEA AVE
UIA 3 7 12 18 2~ 31 38 ~6 ~6 ToUl SPEEO OIR 3 7 12 18 2~ 31 38 ~6 ~6 TOUl SPEED
II 'J.' 1.2 J.a I.e e.3 • 6.8 10.6 .. 0.2 0.9 1.5 0.9 0.2 3.8 10.3....E J.~ 1.~ 3.0 l.J .) .1 ;.1 7.0 1C.3 ....E 0.3 ).9 2.~ 1.9 0.3 '.8 11.0.;E vol 1.1 1.8 J.9 • ~.1 9.~ "E 0.3 1.' 1.5 0.6 • 3.~ 8.9
E"E 0.3 ,.6 :l.T j.2 1.7 7.7 ENE 0.2 0.6 0.3 0.1 • 1.3 7.6[ J.B 1.~ 1.~ J.~ ~.O 7.3 E 0.8 1.~ 1.5 0.8 0.2 ~.7 8. ,
ESE J.8 2.1' 3.6 1.3 0.2 7.9 9.1 ESE 0.7 2.(' 3.5 2.1 0.3 8.5 10.0SE 0.8 3.5 5.2 1.~ 0 .. 1 11.0 8.5 SE 0.6 3.3 ~.~ 1.6 0.1 10.1 8.9SSE J.~ 2.,) 2.8 1.) 0.1 6.5 8.8 SSE o.~ 1.7 3.0 1.1 001 6.~ 9.3
S J.5 1.9 3.6 2.9 0.8 c.2 J •.1 9.9 11.' 5 0.5 2.2 ~.~ ~.~ 1.~ 0.3 13.2 12.3))w '-.1.4 1.) 2.7 3.7 1.9 :".4 10.1 ...C SS. 0.2 1.2 3.9 6.5 3.~ 0.8 0.1 16.1 15.1SW J.3 1.1 2.3 J.2 1.9 0.6 0.1 9.5 1~.6 SW o.~ 1.0 3.0 3.9 3.1 1.1 0.2 12.6 1'.7WSW 0.3 J." 0.7 '.6 o.~ ).1 • 2.7 12.3 wSw 0.1 0.2 0.5 0.6 0.2 0.2 • 1.7 13.7W O,J ,.~ ":.3 0.1 • 1.0 7.C W 0.2 0.3 0.2 001 • • 0.8 8.6w..w 0.2 J.3 J.2 • 0.7 5.9 W... 0.1 0.1 0.1 O.~ 6.~
N. 0.2 ':'.4 C.~ 0.1 ) .1 1.2 8.8 Nw 0.1 VIOl J.1 O.~ 7.6..Nw J.3 J.5 O.T ·J.1 • 1.7 8.1 NNW 0.1 0.2 0.2 C.1 0.7 8.8CALli ... ; ".0 CalM 10.2 10.2TOUl .21.", 19.5 32.3 19.6 6.J 1.5 C.2 100.0 9.1 TOUl 15.~ ll.~ 3C.6 2~. T 9.3 2.~ 0.3 100.0 10.6
16
UQ.l
~ 0 ~-lJ-'~--Ii-~-HJl--!H--,J--JH!-.WH'~---t-t-b't
E
S -20 ~~""""'T~""""i"li'i'",'"
SEPT 75 OCT NOV
N 20 r--------------~---~--~----I
UQ.l
~O
E
N 20 .,.----------------~--~---____r
u ~Iv,Q) -I-h-~~~+J-+-_II_+'.\_____+.l,._jUJj~Ii4!_~Ithtt_l__J+rlI_\h_t_:___ttttHf!ttH_++.+~ \iLi~ 0 ,(: J I:i IE I ~ f ~
~, , iii iii iii iii ii' ii' iii iii ii' , iii iii iii ii' iii iii' iii iii i , , i , i , iii i" i , iii i i rrrrrJMAR APR MAy
S -20
N 12...----------------------__-----..
uQ)
~ 0 +f-:l+-fIflHHl--Il+:-H-I-lJI-II+l+-+----H+++JI.4hI--+lIh--I-:-+J+\jHE
JUNE JULY AUG
Figure 8a. One-year time series of the N-S wind component for West Point.For this chart a positive north component means the wind is from thesouth (Cannon and Laird t 1978).
17
WES
TPTW
INW
X**
**47
40N
-122
-23W
2.9
WES
TPTW
INW
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2.9
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YSST
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ING
7533
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001
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re8b
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tra
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duri
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r(D
ecem
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,19
78).
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a:.....
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~+
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>N
N
lSI .....
,lSI .....
lSI .....
lSI .....
lSl0
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SUM
MER
2."
01
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0.5
0L
00
CYCL
ES/D
AY U-
COM
PONE
NT
~.00
2"."
01
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0.5
0L
00
CYCL
ES/D
AY
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NENT
Figu
re8c
.Fr
eque
ncy
spec
tra
for
the
nort
h(v
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st(u
)co
mpo
nent
ofw
ind
for
Wes
tP
oint
duri
ngsu
mm
er(J
une-
Aug
ust)
(Can
non
and
Lai
rd.
1978
).
WEST POINT WIND-WAVE ROSE
PERCENT OCCURANCE2 4 6 8 10 12
)MAXIMUM STORM CONDITIONS-I1---
Hs =4.9 ~
Ts =4.6 MAXIMUM STORM CONDITIONSHs =6.0 _____
Ts =5.0 PERCENT CALM 16.3
-----MAXIMUM STORM CONDITIONSHs =4.3_____
~TS'4.4
Me~I~~!MS~TOR(;MCONDITIONS
T?4.2
MAXIMUM STORM CONDITIONSHs =4.1Ts=4.1
LEGENDCHARACTERISTIC WAVE
Hs (ft)
Ts (sec)
UP TO 1.0,Ts =2.0Hs=1.0, Ts=2.0 TO Hs=2.5, Ts=3.5
OVER Hs=2.5, Ts=3.5
,., , ..::..,
Figure 9. Annual wave climatology computed for West Point from the windclimatology at SEATAC (Skjelbreia, 1981).
20
Suspended particulate concentrations in the air over the industrializedDuwamish Valley and the tide flats of Tacoma have regularly exceeded established local and national standards since monitoring was initiated (Table 5and Fig. 10). The long-term trend in suspended particulate concentrations overthe region decreased until 1976 and then leveled off or increased slightly from1976 to 1979. Increases in particulates were observed in both industrial andsuburban residential areas in 1979, with seven stations exceeding the nationalstandard of 75 ~g m- 3. Monthly averages above 160 ~g m- 3 have been measuredin the two major industrialized areas.
Of the stations monitoring ozone concentrations, four of ten in 1978and seven of nine in 1979 measured levels that exceeded national standards.Ozone concentrations are higher in summer months due to more hours ofsunlight per day, with maximum concentration normally occurring 10-30 krnsoutheast of major urban centers.
Of the stations monitoring CO concentrations, ten of twelve in 1978 andnine of thirteen in 1979 reported levels that on at least two occasions exceeded an 8-hour average of 9 ppm, the national ?tandard. High ambientlevels of CO occur near congested areas where there is slow-moving motorvehicle traffic and when low-level winds are light and stable meteorologicalconditions exist.
Table 5.--Annual average concentration of suspended particulates lfor stations in the Puget Sound region 1972-1979*
Year Everett Duwamish Tacoma Auburn
1972 60 97 94 551973 53 111 82 631974 40 77 69 511975 36 66 54 381976 45 83 87 491977 43 94 91 541978 45 100 98 541979 50 101 107 62
l(~g m- 3).*(Puget Sound Air Pollution Control Agency, 1972-1980).
21
PUGET SOUND RIR POLLUTION CONTROL RGENCYSDlJl17'---+--~---.:--r--'--+-_""'""'----._---.::--'--+---+----+----t-----c_--+---+----+----t--_------t
TI1T WATER RES
+10 r--
N
~
SUSPENDED PRRTICULRTES1980 RNNURL GEOMETRIC MERNS
(MICRClGRAMS/CU METERI
'"20
. . ., , , , ,. .""-["5
\'\
THUAS TON CO I, PIERCE CO
\
---~~~~_fQ._--------KING CD
!I2IQ.O
i~~~-.o
~ ---1s 52ID.O i
iii KlTSAP CDrPiE~-Ca-----
!
!I2ll5Jl+----+---t---+...::::".-t---+---+---t---+--t---+----+----+---+--t---+---+---t---+----+mo 5Is"o S!O.O z.o D:I.D ~.D '10.0 !5It5.D !!5O,o ~ S1.O 565.D 57O.D .,.,.",0 580.0 ~.D ~ 9!l.O 600.0 &m.£J
UTM (KILOMETERS ERST!
Figure 10. Mean annual particulate concentration for 1980 (Puget SoundAir Pollution Control AgencYt 1980).
22
2.6. Surface hydrology
The mean annual flow for the major rivers of the Puget Sound regionvaries greatly with locality (Williams et a1., 1982). By far the largestinput is from the northern tributaries, with the Skagit River being thelargest single source (Fig. 11).
There are two periods of high stream flow each year (Fig. 12). Oneoccurs during the fall and winter, coinciding with the season of maximum precipitation. The other, in late spring and early summer, is caused by snowmelt in the mountains, augmented by rainfall. Streams rise to near or aboveflood stage several times during each rainy season; the highest flood crestsoccur in late fall and early winter. Stream flow also shows large variabilityfrom year to year (Fig. 12b).
3. Large-scale Meteorological Characteristics
Throughout the winter the synoptic (large-scale) meteorology over PugetSound is characterized by a sequence of cyclonic (low sea-level pressure) disturbances (Klein, 1957) that move over or to the north of the region. Thissequence is interrupted infrequently by anticyclones (high sea-level pressureregions). Spring and autumn are transition periods when the frequency andintensity of cyclones diminish and increase respectively. Summer is markedby light cyclonic activity and by long periods of anticyclonic influence dueto the intrusion of a high-pressure region from the north Pacific.
Winter cyclone tracks for the Northeast Pacific indicate that most ofthe air masses affecting Puget Sound have their origin in the central Pacific.While it is difficult to generalize all synoptic weather charts, two typicalstorm types suggest themselves (Reed, 1932). In the first type, designatedLl (Fig. 13a), pressure patterns are associated with a large and extensivelow-pressure area in the Gulf of Alaska and a series of accompanying coldfrontal systems. The center of the low pressure usually drifts slowly,whereas the frontal systems advect rapidly across the Pacific, rotatingabout the center of the low. The warm sector ahead of the front is usuallyof small extent by the time it is in the vicinity of the coast; therefore,classical warm fronts are often weak and diffuse although they are stillassociated with stable air masses.
As the storms approach the coast, they are modified by the effect of thecontinent (Lau, 1979). The surface features of the cold front in Ll oftenrapidly approach the coast and slow, while higher level features continue tomove over Puget Sound. The severity of the weather associated with the frontis not always as great as it is when the storm system is over the Pacific.Thus, it is often difficult to forecast the timing and severity of frontalfeatures over Puget Sound by extrapolating the speed of the storm while itis over the Pacific. The CYCLES project is an extensive study of the mesoscale and microsca1e organization and structure of clouds and precipitationin storms affecting western Washington (Hobbs, 1978; Hobbs et a1., 1980;Parsons and Hobbs, 1982).
23
N ~
48
0
47
0
124
012
30
122
0
Fig
ure
11.
Mea
nan
nual
runo
ff(m
3s-
l)fo
rPu
get
Soun
d.P
erio
dsof
reco
rdva
ry(W
illia
ms
etal
.t
1982
).
MEAN MONTHLY RUNOFF
1400
SKAGIT
SUM
AUG SEPJUNAPR
MONTH
FEBDEC
/----, ~--\
/' / \/ " // \
/ - / \/ ---- \/ \
/ '\.'\.
~------ ... _-- -----........" SNOHOMISH...- ------------------- " '---
.-- '--",------. PUYALLUPO-+----.---....-----r---..,.------,-----,
OCT
200
400
1200
1000
lJ) 800........l""l
ELLLL0 600z:::::l0::
Figure 12a. Mean annual cycle of discharge for Puget Sound's three majortributaries (Williams et al., 1982). The period of record for the Skagitwas 1941-1979, the period for the Snohomish was 1963-1979, and the periodfor the Puyallup was 1914-1979.
25
AN
NU
AL
RU
NO
FF
1200
SU
M
SK
AG
IT
N 0'\
lJ)
~E - LL LL o Z :::> 0::
1000
80
0
60
0
40
0
20
0
//'\
y/'
/"
/'
\/',
/\
---/
\...
/\
/'
'"-
-/
\/
"'\
/'
"'-
-//
'-'-
v/
\/
\/
'....
SN
OH
OM
ISH
-v
v
----
-.....
..~~~-
----
----
----
----
----
-_.-
~....""
,",'-~-._--.
--.-
-"""
,-'
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---
PU
YA
LL
UP
......._-"
"'-...,
......-
-
78
79
76
74
727
068
66
oI
II
II
II
II
64
YE
AR
Figu
re12
b.In
tera
nnua
lv
aria
bil
ity
ofdi
scha
rge
for
Puge
tSo
und1
sth
ree
maj
ortr
ibu
tari
es(W
illia
ms
etal.
,19
82).
a
.~.~~
b
.~.~-
....
d
Figure 13. Typical weather patterns affecting the Pacific Northwesta) Ll, b) L2, c) HI, d) H2 (Maunder, 1968; Overland, 1981).
27
In the second type of storm, L2 (Fig. 13b), small disturbances form inthe central Pacific and move across the Pacific on a northeast trajectory,commonly passing parallel to the coastline or crossing over British Columbia.Such systems can rapidly intensify as they propagate north, seaward of thecoastline, and produce some of the most severe P~get Sound weather, such as theColumbus Day storm in 1962 (Lynott and Cramer, 1966). A subset of this typeis small synoptic-scale cyclones or II vortices ll
" that form in the western Pacificbehind major frontal bands such as Ll (Reed, 1979; Mullen, 1979; Locatelli etal., 1982).
At some time during most winters an upper-level blocking ridge of highpressure will develop over northwest Canada, accompanied by high pressureover the Puget Sound region, HI (Fig. 13c). As a result, there are clearskies due to air mass subsidence induced by the high-pressure area, nearfreezing temperatures, and very stable air in the surface layer of the atmosphere (Overland and Walter, 1981).
The summer season in Puget Sound is influenced by marine air from thePacific moving over the region by way of the Strait of Juan de Fuca (Mass,1982). From the end of June through August the synoptic situation is characterized by a marine high-pressure system influencing the area, H2 (Fig. 13d).This high-pressure influence leads to a dry season with many clear days, warmtemperatures, and prevailing winds from the west to northwest. Cyclonicdisturbances may still occur, but their severity is greatly lessened and theirfrequency is likewise diminished compared to winter.
The spring season is not significantly different from winter except thattemperatures are higher due to increased insolation; the frequency of cyclonicdisturbances decreases, and their distribution over time is irregular. Thestrength of the upper-level flow diminishes in intensity as spring progresses.
Autumn is another transition period. A common characteristic of earlyautumn is the continuing influence of the Pacific high-pressure system in thearea. The high-pressure ridge eventually breaks down, shifting the prevailing winds to southwesterly and strengthening the upper-level flow. With thisshift come the cyclones and fronts associated with winter.
The frequency of occurrence of these major map types is summarized byTable 6 derived from Maunder (1968). During winter months, December throughFebruary, lows predominate over highs by 3:1; type Ll forms 62% of the observedlows. By contrast, for the summer months, July through September, type H2dominates on 48% of the days. Further discussion of typical synoptic weathersituations for western Washington is given in Halladay (1970).
28
Table 6.--Number of days per month with synoptic weatherpatterns L1, L2, HI, H2*
Weather Monthpattern
J F M A M J J A S 0 N 0 YEAR
L1 14 10 7 12 7 4 5 5 5 14 10 13 106
L2 9 4 11 10 6 6 4 7 6 4 13 11 91
HI 4 2 3 0 1 1 1 1 3 6 3 4 29
H2 3 14 8 7 13 15 16 14 16 5 2 3 116
*Adapted from Maunder, 1968.
29
4. Regional Meteorological Phenomena
4.1. Overview
Regional weather phenomena are the result of the superposition of forcingon synoptic (1000 km), meso- (50 km), and local (5 km) scales. The interaction of synoptic-scale weather patterns and the topography of the regiondetermines mesoscale and local meteorological features. For example, theOlympic Mountains affect wind and precipitation patterns because air massstability confines airflow to the low-level marine channels, the N-S-orientedCascade Mountains have a blocking effect on large-scale weather systems, andthe proximity of the inland waters to the Pacific Ocean to the west and thehighlands to the east of Puget Sound produces a strong diurnal variation ofthe summer wind pattern due to generation of land and sea breezes and valleywinds.
The mountains restrict the free movement of air at sea level, whichprevents geostrophic adjustment between pressure and wind, so that the earth'srotation has little effect on the direction of the wind; winds blow predominantly from high- to low-pressure in a direction dictated by the orientationof the low-level channels. Since Puget Sound is oriented at approximately aright angle to the Strait of Juan de Fuca, high pressure to the east giveseasterly (i.e., down-gradient) winds in the Strait of Juan de Fuca and lightwinds in Puget Sound, while low pressure to the north gives strong southerlywinds in Puget Sound and light winds in the central part of the Strait of Juande Fuca. Wind speed (in knots) for the Strait of Juan de Fuca is roughly tentimes the difference in the sea-level pressure (in millibars) at Bellinghamand Quillayute; the wind speed for Puget Sound is roughly ten times the difference in pressure at Olympia and Bellingham (R. Anderson, personal communication; Overland, 1981).
Because of the different orientation of Puget Sound and the Strait ofJuan de Fuca, a frontal passage can lead to differing time sequences of windsin the two regions (Church, 1938). For a typical example (Fig. 14), at 0500Pacific Daylight Time (PDT), the lowest sea-level pressure is at the coast,which creates east winds in the Strait of Juan de Fuca. By 1100 PDT, thefront has passed over the inland waters, and pressures are beginning to increase to the south behind the front giving rise to southerly winds in PugetSound. By 1700 PDT, the front has passed to the northeast of Bellingham, andpressures have increased at the coast reversing the wind direction to westerlyin the Strait of Juan de Fuca. Thus, the winds in Puget Sound have increasedand then decreased from the south during the frontal passage, while the winddirection in the Strait of Juan de Fuca has reversed from east to west.
The following sections review studies that have recently led to a considerable increase in understanding of the factors affecting the meteorology of thePuget Sound region.
30
49
0
~'~--1:'
W1
48
I.....
.'-
--Q
UI\
I,o
vute
~,.
,'"
\..J
'I
)\,IIOY
Ule9
92
mb
~
\4
r-j
VJ
VVrU~~f:
j,I
I11
00P
O] \
1250
124
0I<b
o12
20
Fig
ure
14.
Typ
ical
loca
lw
ind
pat
tern
sfo
rth
epa
ssag
eof
afr
ont
thro
ugh
wes
tern
Was
hing
ton
(Ove
rlan
d,19
81).
4.2. Gap winds and bora
Several times during most winters a cold high-pressure area is established east of the Cascade Mountains with a low-pressure system offshore(Fig. 15a). This situation results in a large east-west pressure gradientover the Puget Sound region and the formation of locally strong and at timesdestructive winds. Reed (1931) applied the term "gap winds" to the strongeasterly winds observed in the Strait of Juan de Fuca under these conditionsand characterized these winds as II not being, properly speaking, gradient windsin that geostrophically balanced pressure gradients are totally inadequatealone to account for the velocities observed." He defined "gap winds" as theflow of relatively homogeneous air in a sea-level channel with a source regionor reservoir at one end. A component of the pressure gradient parallel to thechannel causes the flow to accelerate along the channel. Reed also concludedthat the high velocities in the Strait of Juan de Fuca were due to a venturieffect caused by the converging sides of the channel.
In a more recent investigation of gap wind conditions, Overland andWalter (1981) combined high-resolution, low-level (50-m) wind fields derivedfrom aircraft flights over the Straits of Juan de Fuca and Georgia with surfacedata and upper-air soundings. It was found that the presence of convergingsides of the channel was incidental to the increased wind speeds and thatacceleration due to the pressure gradient along the channel alone was sufficient to explain the observed wind magnitudes. An example for the period2040-2400 GMT 23 February 1980 is shown in Fig. 15b. Winds in the Strait ofGeorgia were light and variable where the pressure gradient was flat; in theeastern part of the Strait of Juan de Fuca the flow was generally disorganizedbut tended to have an easterly component. In the central and western portionof the Strait of Juan de Fuca the component of the pressure gradient along theaxis of the channel remained nearly uniform, while the winds increased to14 m s-l at the entrance to the Strait. Vertical wind speed measurements fromthe aircraft indicated that subsidence was occurring over the inner part ofthe Strait of Juan de Fuca and the Strait of Georgia, whereas vertical motionwas upward west of 124°20'W.
For the inland waters of Puget Sound and the Strait of Juan de Fuca, theacceleration of the wind provides the primary balance to the component of thesea-level pressure-gradient force imposed by the synoptic weather situationalong the direction of the various channels. For flow at constant height theincrease in wind speed due to a constant sea-level pressure gradient is givenby the Bernoulli equation:
(1)
where u is velocity, Uo is an initial velocity, ~p is the pressure difference,and p is a density.
A situation similar to 23 February occurred on 13 February 1980, but inthis case the major pressure gradient was situated over southern BritishColumbia (Fig. 16a). The pressure gradient accelerated the cold, dry continental air from the interior of British Columbia through the Fraser River
32
45°
~4
0°
a
Figu
re15
.(a
)S
ea-l
evel
pres
sure
anal
ysis
for
00GM
T24
Febr
uary
1980
for
wes
tern
Was
hing
ton
(Ove
rlan
dan
dW
alte
r t19
81).
55°
50°
45
°
48
0
126°
W
b
1250
1240
1230
49
0
{<V~~l-48°
15.
(b)
Loca
lw
ind
fiel
don
23Fe
brua
ryan
dse
a-le
vel
pres
sure
anal
ysis
for
21GM
T23
Febr
uary
1980
for
the
Str
aits
ofJu
ande
Fuca
and
Geo
rgia
(Ove
rlan
dan
dW
alte
r t19
81).
Fli
ght
leve
lw
ind
mea
sure
men
tsar
esh
own
assm
all
win
dar
row
s.B
old
arro
ws
with
circ
les
indi
cate
surf
ace
stat
ion
orbu
oyre
port
s.W
ind
conv
entio
nis
inkn
ots.
The
heav
yda
shed
line
atth
een
tran
ceto
the
Str
ait
ofJu
ande
Fuca
repr
esen
tsa
tran
siti
on
from
subs
iden
ceon
the
nort
han
dea
stsi
deto
posi
tive
vert
ical
mot
ion
seaw
ard
ofth
eli
ne.
4?O
122°
123°
124°
126°
4?O
40
°
115°
120°
125°
140°
135°
130°
125°
._-
126°
W12
5°12
4°12
3°12
2°
~16
lIiiJi
!I
.5
0°
55°
49.N1O~
'UU,~~
r4~
/'"
"..
r.
'-0.
r_:;--~
1008
.•III
.\\~
........
.<.
_•
09
04
5°
W5
0°
+=-
48
°1l?
''l~~1;t-
r48 °
40
°4
5°
ab
Fig
ure
16.
(a)
Sea
-lev
elpr
essu
rean
alys
isfo
r00
GMT
14Fe
brua
ry19
80(O
verl
and
and
Wal
ter
t19
81).
(b)
Loc
alw
ind
fiel
don
13Fe
brua
ry19
80an
dse
a-le
vel
pres
sure
anal
ysis
for
21GM
T13
Febr
uary
1980
(Ove
rlan
dan
dW
alte
rt
1981
).
49°N
480
47·-
c
1260
126°W 1250
1250
1240
2100 GMT13 FEB 80
1240
123 0
1230
1220
49"
480
470
1220
Figure 16. (c) Wind and dewpoint fields from surface and aircraftreports 21-24 GMT 13 February 1980 (Overland and Walter t 1981).
35
Valley near Vancouver (Fig. 16b). This dry air displaced the more moist,marine air as it flowed across Georgia Strait and was ultimately channelledout the Strait of Juan de Fuca (Faulkner, 1980). The change of dewpointtemperature marked the air mass boundaries (Fig. 16c). The dry air maintainedan essentially constant velocity while spreading laterally and growing indepth, as shown by a downstream increase in inversion height. The momentumcontained in the jet increased with downstream distance due to the presence ofa pressure gradient along the flow direction. The eddy-like feature beyondthe entrance to the Strait of Juan de Fuca, which had light SE winds to the westof its boundary and strong (10-12 m s-l) winds from the E to the east of theboundary, may have been due to the presence of a hydraulic jump. Verticalwind speeds as recorded by the aircraft were downward at 1 ms-1 on the eastside and upward at 0.4 ms-1 on the west side of the boundary.
Another response of the flow in Puget Sound to pressure differences isthe creation of a downslope wind called a bora, which blows out of the passesin the Cascade Range when high pressure exists to the east of the mountains.Since the source region for the air in eastern Washington is often very cold,the adiabatic heating of the air upon descent out of the passes is not sufficient to raise the temperature to levels equal to ambient conditions in thePuget Sound Basin, so the cold air spreads out over the lowlands. Reed (1981)discussed a windstorm that led to a bora-like flow in Stampede Pass and gapwinds in the Columbia River Gorge. Figure 17 shows the extremely largegradient of sea-level pressure in the vicinity of the Cascades for 28 Novem-ber 1979. This gradient was for the most part fictitious, merely indicatingthat the mountain barrier sustained a large pressure difference between the coldair in central and eastern Washington and the warm air over western Washington.An E-W cross section (Fig. 18) of potential temperature across the State ofWashington from Spokane (GEG) to Quillayute (UIL) showed the intense horizontaltemperature gradient that developed over and to the lee of the mountains asthe upper-level inversion tilted and lowered in the subsiding airflow.Rewriting (1) using pressure coordinates gives:
aDg ax ax , (2)
where g is gravity, D is the geopotential height deviation from the standardvalue for a particular pressure level and ax is the difference in horizontaldistance between the end points of the trajectory. Calculations using Eq. (1)in the Columbia River Gorge and Eq. (2) for flow in the lee of Stampede Passestimated sufficient wind magnitudes to account for those observed.
4.3. Orographic low-pressure formation in the lee of the Olympic Mountains
During the winter (December-February), synoptic weather patterns giverise to S-SW flow conditions over the Puget Sound region 75% of the time.When synoptic-scale winds are from the south-to-southwest, the Olympic Mountains can induce the formation of a low-pressure area directly in the lee·of the mountains over Puget Sound or the Strait of Juan de Fuca (Overland etal., 1979), and Vancouver Island can induce low pressures over the Strait of
36
\-0
74
54
____-~~
--l
a.~
'.4
4)
120
0
-06
487
\@ \ i l--
---
----
--_
--:-
----
-\
_~
:48
\ .
~E"TI
(-I~
_?;-
o470
I46
I_
80
45
8. \
48
+-0
84
84
40
42
44
46
/25
0
50
°~R
\.A"
" '\0>~
\f ~
~\\
I1--
----
Figu
re17
.Su
rfac
em
ap,
12GM
T28
Nov
embe
r19
79.
Isob
ars
are
draw
nat
inte
rval
sof
2m
b.T
empe
ratu
re(O
e)is
plot
ted
tole
ftof
stat
ion
and
pres
sure
(mb)
tori
gh
tof
stat
ion
(Ree
d,19
81).
W -....I
w 00
mb
50
0
60
0L
3/0
70
0
80
0
90
0
~280~~--
---10
00
UIL
100
km
Figu
re18
.C
ross
sect
ion
ofpo
tent
ial
tem
pera
ture
(OK)
acro
ssth
est
ate
ofW
ashi
ngto
n(R
eed
t19
81).
Sta
tion
UIL
isQ
uill
ayut
et
SEA
isS
eatt
let
and
GEG
isSp
okan
e.
4 4
Georgia (Myers, 1966). The importance of the presence of such a low-pressurearea was dramatically demonstrated on 13 February 1979 when the Hood Canal Bridgesank ~uring surface winds in excess of 50 m s-l. Reed (1980), who analyzed themeteorological conditions for this event, found that although the gradient ofsea-level pressure at the bridge was strong due to the synoptic pressuregradient, it was greatly enhanced by the formation of a mesoscale low-pressurearea in the lee of the Olympics (Fig. 19). In the restricted channels ofPuget Sound the air flow at the surface accelerated toward the low pressureproducing the observed high wind speeds. In contrast, Walter and Overland(1982) made measurements with the NOAA P-3 aircraft on three days duringS-SW conditions in February and March 1980 (Fig. 20a-f) and found a regionof light wind speed and flat pressure gradient in the lee of the OlympicMountains and only slight troughing in the pressure field over the easternStrait of Juan de Fuca.
To explain this difference one needs to consider a non-dimensional number,the internal Froude number, F, which compares the momentum of the incidentflow to the stratification of the flow. This number is the critical parameterin determining whether the upstream air will go over (large F) or around(small F) an isolated obstacle such as the Olympic Mountains. For a fluidhaving continuous stratification the Froude number is given by
F - V- hN 'e
(3)
where V is upstream flow velocity, h is the height of the mountain, and Ne isthe stratification parameter, the BrUnt-Vaisala frequency,
N 2 =9.- dSee S dz'e
(4)
where g is gravity, Se is the equivalent potential temperature, and z is thevertical coordinate. The vertical derivative of equivalent potential temperature accounts for stratification due to moisture as well as ambient temperature.On the three days discussed by Walter and Overland (1982), the boundary layerwas slightly stable throughout its depth with the internal Froude number inthe range F = 1.0-1.4. For the Hood Canal Bridge storm a smaller value of Netogether with high upstream winds led to a calculated value for F of 4.6.
For strong relative stratification, the primary flow about an obstacleis in quasi-horizontal planes (Fig. 21a and b) where the flow in each planeis given by a two-dimensional potential solution defined by the contour ofthe terrain at that level (Drazin, 1961; Riley et al., 1976; Hunt and Snyder,1980). Small vertical displacements of the streamlines passing around theside of the obstacle are due to the need for the potential energy to decreasein order to balance the increase in kinetic energy of the flow around theobstacle. Although the Froude numbers for the low wind studies in Walter andOverland (1982) were in the range of 1.0-1.4, the pressure and wind fields(Figs. 20 b,d,f) show qualitative agreement with experimental results for
39
Figure 19. Regional surface map for 12 GMT 13 February 1979 (after Reed,1980). Isobars are drawn at one millibar intervals (dashed at higherelevations). Winds are in knots. Maximum gusts (G) at observation timeand in preceding hour are plotted below stations.
40
+::> ......
40
°
a11
5°
49°N 48
°
126°
W
1260
b
125°
1250
124°
1240
123°
1230
122°
49
°
48
°
47
0
1220
Fig
.20
.(a
)Se
a-le
vel
pres
sure
anal
ysis
for
00GM
T19
Febr
uary
1980
and
(b)
mes
osca
lew
ind
and
pres
sure
fiel
dat
21GM
T18
Febr
uary
1980
.
~ N
45
0
c
1250
1200
/._
II
40
0
49
°N 48
0
47
0
dl2
60
126°
W12
50
1250
124
0
1240
123
0
123
0
122
0 49
0
48
0
47
0
1220
Fig
.20
.C
c)S
ea-l
evel
pres
sure
anal
ysis
at00
GMT
29Fe
brua
ry19
80an
dCd
)m
esos
cale
win
dan
dpr
essu
refi
eld
at21
GMT
28Fe
brua
ry19
80.
49
0
47
0
48
0
1220
122
0
J
123
0
12
30
1240
1240
125012
50
1019
1020 10
21 10
22
-I
126°
W
1260
f
47
0
48
0
49
°N5
50
1150
e
40
0
-1=>0
W
Fig
ure
20.
(e)
Sea
-lev
elpr
essu
rean
alys
isat
00GM
T10
Mar
ch19
80an
d(f
)m
esos
cale
win
dan
dpr
essu
refi
eld
at21
GMT
9M
arch
1980
.
.j:::>
.j:::>
~---
~-:$"-
\£
----
---~.",.
~--:.
...~~,-
'--:
~.(<!'
""'-
,,"'-
-,-
)&
...
....
.
--~
---
--'
....-:~
....
Figu
re21
a.Pl
umes
from
upw
ind
stac
ksat
vari
ous
elev
atio
ns(H
unt
and
Snyd
er,
1980
).To
pis
for
F=
0.2.
Flow
isco
nstr
aine
dto
mov
ep
rin
cip
ally
inho
rizo
ntal
plan
es.
Asl
igh
thy
drau
lic
jum
poc
curs
just
dow
nstre
amfro
mth
eto
pof
the
hil
l.B
otto
mis
for
F=
0.4.
Her
eth
eflo
wis
able
tom
ove
fart
her
inth
ev
erti
cal
dir
ecti
on
,an
dth
ere
gion
whe
reth
eflo
wgo
esov
erth
eto
pis
broa
der.
Flow
goin
gov
erth
eto
pse
para
tes
half
-way
dow
nth
ele
esl
ope.
Nu
me
rica
lR
esu
lts
,.. X1(
cm)
o3
04
0
Exp
eri
me
nta
IR
esu
lts
50
--:;
......"'.•_
;,.I~!:-••
r:,~..._.
,.,•.~...
,·,.,.·..,
.·.._·,,·
·
~
u•
t:;--,~;;:Y
/8:1
"/
--L
10
Figu
re21
b.C
ompa
rison
ofex
peri
men
tal
and
anal
yti
call
yco
mpu
ted
(Dra
zin
t19
61)t
stre
ak
line
sin
the
hori
zont
alpl
ane
atm
id-l
evel
ofa
Gau
ssia
n-sh
aped
obst
acle
for
aFr
oude
num
ber
of0.
154
(Ril
eyet
al.
t19
76).
low Froude number flow. However, from the magnitude of the isotherm displacement in cross-section plots of constant e surfaces along the east side and inthe lee of the Olympics, it was evident that the flow was approaching thetransition region between small and large Froude number theory.
For the case where F » 1, Smith (1980) developed a hydrostatic linearmodel for stratified flow over an isolated mountain. His results for a bellshaped mountain showed an asymmetric perturbation surface pressure field withhigh pressure over the windward slope and low pressure on the lee side. Thispressure distribution caused the surface streamlines to be deflected aroundthe sides of the mountain and to maintain a permanent outward deflectiondownstream. Horizontal divergence in the lee of the mountain caused a sinkingof warm air from aloft and a decrease in the vertical distances between downwind, low-level, constant-density surfaces. When this perturbation pressurefield is added to the background synoptic-scale pressure field (Smith, 1981;Fig. 22), the result is in agreement with the sea-level pressure analysis forparameters from the Hood Canal storm (Fig. 19).
Reed (1980) indicated that in the vicinity of the Hood Canal Bridge on13 February 1979 the pressure gradient was a maximum of 6 mb in 15 km or0.4 mbkm-1. Comparison of the observed winds at the time of the bridge collapse (from Reed, 1980, Table 2) with those calculated for a confined channelfrom Eq. (1) and a value of the pressure gradient of 0.4 mb km-1 shows goodagreement (Table 7).
When the internal Froude number has a value on the order of 0.5-1.5, theflow response in the lee of the Olympics will be relatively benign with lightand variable winds. However, when the Froude number is of order 4-5, a closedmesoscale low-pressure region will be induced in the lee of the mountains.The flow at the surface in the restricted channels of Puget Sound responds bya rapid acceleration toward low pressure to give extreme wind speeds in alocalized area.
4.4. Effects of orography on precipitation--the Puget Sound convergence zoneThe surrounding mountains not only have a strong effect on the wind
fields but also on the precipitation patterns in Puget Sound as shown by Mass(1981) and Parsons and Hobbs (1982). In the spring transition months (AprilJune), when high pressure builds northward into the eastern Pacific Ocean, thecoastal winds change from a predominantly southerly to a northwesterly direction. As southerly winds veer to the northwest after a frontal passage at thecoast, there is a narrow range of wind directions and speeds (Fig. 23) wherethe air will simultaneously flow eastward both north and south of the OlympicMountains. This flow pattern results in the formation of an area of convergence over Puget Sound (Fig. 24). Mass (1981) studied 25 cases of thisconvergence phenomenon and concluded that the controlling parameters were thewind direction and speed on the Washington coast, although most convergencezone events were also associated with weak atmospheric stability typical ofspring. He found that a convergence event was most likely to occur when, forfour continuous hours, the Hoquiam wind direction was between 2600 and 3200
and the wind speed ranged from 2 to 7 m s-l. AlthoUgh convergence events canoccur any time of the year, they are most probable from April to June when twoto four major events per month are expected.
46
~ -......J
----
----
----
----
--
-------------- -----------
o5
010
0km
,,
I
-4 -3 -2 -Io I 2 3 4m
b
Fig
ure
22.
Sum
ofth
epe
rtur
bati
onpr
essu
refi
eld
from
Sm
ith'
shy
dros
tati
cli
nea
rm
odel
and
ahy
poth
etic
alsy
nopt
icpr
essu
refi
eld
(Sm
ith,
1981
).
Table 7.--Comparison of winds reported by Reed (1980) in Hood Canal14-15 GMT 13 February 1979 and those calculated from Eq.1*
Bridge9.25 km SSW18.5 km SSW
Observed-140 m s
3022.5
Calculated
40.5 m s-l
3322.5 (assumed)
*Initial velocity used for the calculation is 22.5 ms-l.
48
N36
8\S
E
o
Figure 23. Polar representation of the wind speed and direction atHoquiam, Washington, during ten convergence zone events (Mass, 1981).
49
[May 2-:19781900GMT
IMay 2,1978l?.QOOGMT
\.\
May 2,/97812100G~T I
Figure 24. Streamlines over the Puget Sound area during the convergence zone event of May 2-3, 1978 (Mass, 1981). The position ofthe surface convergence line is indicated by a dashed line.
50
A composite vertical structure of the convergence zone was constructed byMass (1981), who indicated that it is similar to that of a classical front.Northerly winds enter Puget Sound and propagate as a wedge into the pre-existing southerly winds (Fig. 25). The windshift line separating the opposingflows slopes upward to the north. Enhanced clearing is observed both northand south of the main convergence zone cloud band. Mass (1981) indicated thatthe clear area north of the zone is due to subsidence associated with thesurface divergence created as air flow in the eastern Strait of Juan de Fucasplits and moves both north into the Strait of Georgia and south into PugetSound. The clear region to the south of the zone is due to subsidence of airin the mesoscale circulation set up above the convergence line.
The presence of the convergence zone has pronounced effects on the cloudiness, temperature, and precipitation patterns over the region, and its effectscan be seen in Figures 26 a-c, which are composites of these parameters forthe cases studied by Mass (1981) plotted with reference to the location of theconvergence line. Most of these convergence events showed a band of cloudsacross central and northern P~get Sound with the southern boundary close tothe windshift line. These clouds were generally shallow, with tops between1500 and 2500 m in the central Sound and 3000 m near the mountains. Thelowest cloud deck in the Sound frequently reached to the ground.
The effect of the convergence zone on precipitation can be seen in thelong-term climatology. Mass (1981) constructed a N-S cross section of monthlyprecipitation for Puget Sound (Fig. 27). There is a normal annual cycle atall stations except in the northern Sound where there was sustained precipitation through May and June caused by convergence zone precipitation.
Parsons and Hobbs (1983) studied the effects of orographic features inthe Puget Sound region on mesoscale structures and precipitation processes indifferent types of rainbands embedded in synoptic-scale storms as they passacross the region. They studied warm-frontal, warm-sector, narrow and widecold-frontal, and post-frontal rainbands and found that the influence oforography was dependent on the rainband type, the size of the orographicfeature, and the airflow. Figure 28 shows that a large percentage of precipitation from warm-sector (i.e., pre-frontal) rainbands occurs at three coastalstations due to slight lifting of the airmass and from post-frontal rainbandsat three stations about 100 km inland, where precipitation is considerablyenhanced over the windward slopes of the Cascades. Local airflow convergencecaused by the restricted flow in channels of the Puget Sound Basin also playedan important role in enhanced post-frontal precipitation.
4.5. Diurnal wind variations--the sea breeze and valley breeze
In the warm months of the year the wind field shows a strong diurnal variation that is related to differential heating between the land and adjacentwaters and heating on the mountain slopes. Staley (1957) presents hodographs-plots of the rotation of wind vector end points with time of day (Fig. 29)--for July 1950, where resultant winds were derived by averaging components of thewind observed at each hour during the day over a month. In the Strait of Juande Fuca, Port Angeles showed W-NW flow and counterclockwise rotation whileVictoria showed southerly and southwesterly flow with clockwise rotation.
51
800-
1r6
I-.....
........
...-.
...~
........
w850~
Iw l.1
..
........
~r4~
"t
"\
..c
9°°1
EI
Cf)
I0
<.T1
,\
Iz
N
J, ',
\2<
{950~.-
/'
Cf)
........
-...
'"".
:J 0
"""
:::r:.-
•.....
........
..."~
..-
t-1
00
0C
lea
rC
lou
dy
IC
leo
ra
NS
urf
ace
SC
onve
rgen
ceL
ine
Figu
re25
.Sc
hem
atic
view
ofth
elo
w-l
evel
flow
duri
nga
conv
erge
nce
even
t(M
ass,
1981
).
LOWEST DECK20
ao'----J'--:8::-'-:7::-'--=-6-'--=-5-'-4~3-'---:-2...L-1--L...:0--'---_-1L_2,,---1-_3,,---1-_4--L._-=-5...L_-6...L_-7--'-----'_8
COMPOSITE ZONE RELATIVE TO CONVERGENCE ZONE
~
uwoo~
o...JU 10t-Cf)W~o...J
U.oa::wCD~~
z
TEMPERATURE COMPOSITE
b
- - r-
- r-
r-
-f--
-'--
u.~
z 3ot- 2«> I
~ 0
~ -I
; -2
~ -3w~ -4wt- 4 3 2 I 0 -I -2 -3 -4
N COMPOSITE ZONE SCf)tZW> 40wz9 30t-«t-
~ 20uwa::a. 10u.o
~ 7 6 5 4 3 2 I 0 -I 2 -3 -4 -5 -6 -7 -8 C~ COMPOSITE ZONESZ RELATIVE TO SURFACE CONVERGENCE LINE
Figure 26. (a) Summary of the number of times the lowest cloud deck inPuget Sound occurred in each composite zone during five convergence zoneevents (Mass, 1981). (b) Temperature deviations (OF) from the PugetSound mean for each composite zone (Mass, 1981). (c) Summary of thenumber of precipitation events that occurred in each composite zoneduring ten convergence zone events (Mass, 1981).
53
,
••,•
•,,I
Rain Shadow /,\ --- N. Sound /
, C. Sound '\ _.-.- S. Sound ,I,
\ /, ,
\. /\, i
\", I ., \ ,
~ '\ I f'~ . "~:
I" \.. \.. ,/,'.~.~ I '
1'1 '. - \ !I.'I I ". \ /:'. , , , ~ ,
---------..",.' " '" \ //. ' .:'to ..-," ---- .
I •
2
6
8
4
O---,r---___.,.----r--...,.--~-r__ -___.,.-.......,...-_r__-_r__---...I
J F M A M J J A S 0 N
Figure 27. Annual variation of precipitation for the rain shadow andnorthern, central, and southern Puget Sound regions (Mass, 1981).
54
50
40
30
20
10oL-l----l.:..:.:....:..:.Il....L.II _
LONG BEACH
50
40
30
20
10
°CHEHALIS
WARM-SECTOR;":'.:::; NARROW COLD-FRONTAL.. ' .:
WIDE COLD-FRONTALPOST-FRONTAL
O.......--&o.:~ ........
ELMA
50
40
....o. ",".....
. '"0.- .:':'~'~'~
50
40
30
20
10
z«0::
--l
~oI-I.J....oW<.9
~ZwU0::WCl.
50
:".: ~;~::............: :....•" .1".". ".o. "0
°OLY~':~IA
Figure 28. Percentage contributions to total precipitation at threecoastal stations (Long Beach, Moclips, Pt. Brown) and three inland stations (Chehalis, Elma, Olympia) from warm sector, narrow cold-frontal,wide cold-frontal, and post-frontal rainbands on 8 December 1976 (Parsonsand Hobbs, 1982). Note the large contribution from warm-sector rainbandsat the coastal stations and the large contribution from post-frontal rainbands at the inland stations.
55
VICTORIA
4.0
2.0
18
-2.018
PORT ANGELES
1.02.0
1.09 12
-'~D12
0-1.5- 0
1521 18 21 18
1.0
EVERETT OLYMPIA SEATACAIRPORT
Figure 29. Resultant wind hodographs for stations in the Strait ofJuan de Fuca t north t central t and south Puget Sound for July 1950(StaleYt 1957).
56
6. Acknowledgements
This work is a contribution to the Marine Services Project at thePacific Marine Environmental Laboratory. We wish to thank Robert Andersonand W. Burton of the NWS Seattle Ocean Services Unit, Don Faulkner, SteveNikleva, and Ron McLaren of the Canadian Atmospheric Environment Servicein Vancouver,. B.C., for their support and encouragement of this project.
We wish to thank Drs. Peter Hobbs, Cliff Mass, Richard Reed, Ron Smith,and James Connell for their contributions and suggestions. We also thankJournal of Fluid Mechanics (Cambridge University Press) for permission to usefigure 21a.
We acknowledge the assistance of Professor Richard Reed, Department ofAtmospheric Science, University of Washington, Seattle, Wash. 98195, in providinga copy of an unpublished manuscript by V.F. Morris titled "A study of meso-scale mountain barrier effects in western Washington and Vancouver Island."
59
and water propIn: Hydrodynamics
Amsterdam,
7. References
Cannon, G.A. and N.P. Laird (1978): Variab"ility of currentserties from year-long observations in a fjord estuary.of Estuaries and Fjords, Nihoul, J.C.J. ed., Elsevier,515-535.
Church, P.E. (1938): Surface details of a warm front in the Strait of Juande Fuca. Bulletin of the American Meteorological Society, 19, 400-402.
Church, P.E. (1974): Some precipitation characteristics of Seattle. Weatherwise, 27:244-251.
Climatolo ical Handbook Columbia River Basin States Hourl Data, Vol. 3,an, : eteoro oglca ommlttee, aCl lC ort west
River Basin's Commission.Critchfield, H.J. (1978): Sunshine and solar radiation in Washington State.
Office of the State Climatologist, Western Washington University,Bellingham, Washington, 98225, 38 pp.
Drazin, P.G. (1961): On the steady flow of a fluid of variable density pastan obstacle. Tellus, 13:239-251.
Faulkner, D.A. (1980): Mesoscale observations of an outflow wind over theSouthern Strait of Georgia. Pacific Region Technical Note 80-022, A.E.S.,Vancouver, B.C., 6 pp.
Halladay, N.E. (1970): Whidbey Island Forecaster1s Handbook, NAV WEA SERVCOM INST 3140.2, U.S. Naval A,r Station, Oak Harbor, Washington, 115 pp.
Hobbs, P.V., R.A. Houze, Jr., and T.J. Matejka (1975): The dynamical andmicrophysical structure of an occluded frontal system and its modification by orography. Journal of the Atmospheric Sciences, 32:1542-1562.
Hobbs, P.V. (1978): Organization and structure of clouds and precipitationon the mesoscale and microscale in cyclonic storms. Reviews of Geophysicsand Space Physics, 16:741-755.
Hobbs, P.V., T.J. Matejka, P.H. Herzegh, J.D. Locatelli and R.A. Houze, Jr.(1980): The mesoscale and microscale structure and organization ofclouds and precipitation in mid-latitude cyclones, I: A case study ofa cold front. Journal of the Atmospheric Sciences, 37:568-596.
Hunt, J.C.R. and W.H. Snyder (1980): Experiments on stably and neutrallystratified flow over a model three-dimensional hill. Journal of FluidMechanics, 96:671-704.
Klein, W.H. (1957): Principal tracks and mean frequencies of cyclones andanticyclones in the northern hemisphere. Research pa7er No. 40, U.S.Weather Bureau, Washington, D.C., 60 pp. CAvailablerom National WeatherService, Techniques Development Laboratory, Washington, D.C. 20233.)
Lau, N.C. (1979): The structure and energetics of transient disturbances inthe northern hemisphere wintertime circulation. Journal of the AtmosphericSciences, 36:982-995.
Locatelli, J.P., P.V. Hobbs and J.A. Werth (1982): Mesoscale structures ofvortices in polar air streams. Monthly Weather Review, 110: 14·17-1433.
60
Analysis of the pressure oscillations at several stations (Staley, 1957;Fig. 30) showed a diurnal component that reached its maximum and minimum laterat Tatoosh Island on the coast than at the eastern end of the Strait of Juande Fuca or in Puget Sound. Pressure differences between stations were greatestin the afternoon and early evening driving the westerly sea breeze, but theexact time of maximum pressure difference varied as different pairs of stationswere considered. For example, the pressure difference between Port Angelesand Bellingham reached a maximum three to six hours after the maximum pressuredifference between Port Angeles and Everett.
Ideally, hodographs should be elliptically shaped, rotate clockwise withtime, and fall in strength during the night and increase during the day reaching a maximum between 1330 and 1830 Local Time (LT). Superposition of otherfactors related to topography, mean flow field, and valley or slope winds uponthe sea breeze, however, leads to distortion of this ideal shape and behavior(Mass, 1982); the existence of counterclockwise hodographs must be attributedto topographic constraints. For example, the maximum wind component towardthe Cascades during the day and toward Puget Sound at night would be expectedon the basis of upslope and drainage winds regardless of sea breeze. In central and northern Puget Sound the winds turn clockwise on the eastern side andcounterclockwise on the western side of the Sound. A similar situation existsin the Strait of Juan de Fuca, where Port Angeles on the Olympic Peninsulashows counterclockwise turning while Victoria on Vancouver Island has anoppositely directed hodograph. The figure-eight-shaped hodograph at Olympiais interesting because Olympia is situated at the boundary between tworegional sea breeze circulations; it is influenced by the Chehalis Gap tothe south and Puget Sound to the north.
5. Summary
The mid-latitude west coast marine climate of the Puget Sound region istypified in summer by a pattern of high pressure and in winter by a sequenceof storms that originate over the ocean to the west. Local variations inclimatic indicators such as precipitation and wind are substantially influenced by the region's topography. The maximum precipitation occurs in earlywinter which results in a bimodal distribution of runoff into Puget Sound:there is a winter maximum associated with increased rainfall and a late springmaximum associated with snow melt. The proximity to the Pacific Ocean and thepresence of Puget Sound has a moderating influence on extreme temperatures inboth summer and winter. Over the waters of Puget Sound the winds near thesurface flow from high to low sea-level pressure as imposed by the large-scale or regional weather pattern. Several local wind phenomena are important,the most notable being the formation of an orographically induced, mesoscalelow-pressure region in the lee of the Olympic Mountains during strong onshorewinds associated with major coastal storms. Such an event produced winds inexcess of 50 m s-l in a localized area of Puget Sound at the time of thedestruction of the Hood Canal Bridge.
57
-..cE-CL
1020
1019
1017
.•.•.•. TTl.. .. '.. .. .. .~....~..
~..."'....
••••
0.3 6.3 12.3 18.3TIME (pst)
2.0
-..cE
1.0 CL<J
Figure 30. Average sea-level pressures at each hour of the day forJuly 1950 at Tatoosh Island (TTl), Port Angeles (PAE), Everett (EVE),Bellingham (BlI) (upper four curves); and sea-level pressure differencesbetween Port Angeles and Bellingham, Port Angeles and Everett, andTatoosh Island and Port Angeles (Staley, 1957).
58
Lynott, R.E. and D.P. Cramer (1966): Detailed analysis of the 1962 ColumbusDay windstorm in Oregon and Washington. Monthly Weather Review, 94:105-117.
Mass, C. (1981): Topographically forced convergence in western Washingtonstate. Monthly Weather Review, 109:1335-1347.
Mass, C. (1982): The topographically forced diurnal circulations of westernWashington state and their influence on precipitation. Monthly WeatherReview, 110:170-183.
Maunder, W.J. (1968): Synoptic weather patterns in the Pacific Northwest.Northwest Science, 42:80-88.
Mullen, S.L. (1979): An investigation of small synoptic-scale cyclones inpolar air streams. Monthly Weather Review, 107:1636-1647.
Myers, R.A. (1966): Lee troughing west of Vancouver Island. CIR-4410, TEC-608,Department of Transport-Meteorological Branch, 5 pp.
National Climatic Center (1980): Local Climatological Data, Annual Summary,Seattle-Tacoma Airport. National Climatic Center, Asheville, N.C.,28801, 4 pp.
Overland, J.E., M.H. Hitchman and Y.J. Han (1979): A Regional SurfaceWind Model for Mountainous Coastal Areas. NOAA Technical Report,ERL-407 PMEL-32, Environmental Research Laboratories, NationalOceanic and Atmospheric Administration, Boulder, Colorado, 34 pp.
Overland, J.E. (1981): Forecasting the Pacific Northwest winds. Castoff,April 1981, 10-13.
Overland, J.E. and B.A. Walter (1981): Gap winds in the Strait of Juan deFuca. Monthly Weather Review, 109:2221-2233.
Parsons, D.B. and P.V. Hobbs (1983): The mesoscale and microscale structureand organization of clouds and precipitation in midlatitude cyclones.VIII: Some effects of orography on rainbands. Submitted to Journal of theAtmospheric Sciences.
Phillips, E.L. (1968): Washington climate for these counties, King, Kitsap,Mason, Pierce. Cooperative Extension Service, Washington State University,Pullman, Washington, 66 pp.
Puget Sound Air Pollution Control Agency (1972-1980): Air Quality DataSummary for Counties of King, Kitsap, Pierce, Snohomish. Puget Sound AirPollution Control Agency, 410 W. Harrison St., Seattle, Washington 98119.
Reed, R.J. (1979): Cyclogenesis in polar airstreams. Monthly Weather Review,107:38-52.
Reed, R.J. (1980): Destructive winds caused by an orographically inducedmesoscale cyclone. Bulletin of the American Meteorological Society, 61:1346-1355.
Reed, R.J. (1981): A case study of a bora-like windstorm in western Washington. Monthly Weather Review, 109:2383-2393.
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61
Reed, T.R. (1932): Weather types of the northeast Pacific Ocean as relatedto the weather of the north Pacific coast. Monthly Weather Review, 60:246-252. --
Riley, J.J., H.T. Liu, and E.W. Geller (1976): A numerical and experimentalstudy of stably stratified flow around complex terrain. u.s. EPA Environmental Monitorin~ Series Report No. EPA-600/4-76-021, Research TrianglePark, North Caro ina, 30 pp.
Schoenberg, S.A. (1983): Regional wind patterns of the inland waters of westernWashington and souther British Columbia. NOAA Technical Memorandum,Environmental Research Laboratories, National Oceanic and AtmosphericAdministration, Boulder, Colorado, (in press).
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Williams, R., H. Pearson, and J. Wilson (1982): Streamflow statistics anddrainage-basin characteristics for the Puget Sound Region, Washington.Technical Reeort, U.S. Geological Survey, Water Resources Division,Tacoma, Washlngton, in press.
62