background research forecasting challenges (1)cold air damming (2)coastal low pressures...
TRANSCRIPT
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WINTER WINTER WEATHER WEATHER
FORECASTING FORECASTING IN THE IN THE
SOUTHEASTSOUTHEAST
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BACKGROUND RESEARCHCollaborative Science, Technology, and Applied Collaborative Science, Technology, and Applied Research (CSTAR) ProjectResearch (CSTAR) Project
*NWS Offices*NWS Offices*NC State University*NC State University*NC State Climate Office*NC State Climate Office
Evaluation of the Real-Time MM5 Modeling SystemEvaluation of the Real-Time MM5 Modeling System*NC State University*NC State University*NC State Climate Office*NC State Climate Office*Capitol Broadcasting*Capitol Broadcasting*NCSC/MCNC*NCSC/MCNC
SPECIAL THANKS TO DR. GARY LACKMANN FOR PERMISSION SPECIAL THANKS TO DR. GARY LACKMANN FOR PERMISSION TO USE SEVERAL VALUABLE POWERPOINT SLIDESTO USE SEVERAL VALUABLE POWERPOINT SLIDES
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FORECASTING CHALLENGES
(1)Cold Air Damming
(2)Coastal Low Pressures
(3)Precipitation Type
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BUILDING HIGH
PRESSURE
CONFLUENCE ALOFT
SURFACE DIVERGENCE
&PRESSURE
RISES
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CAD as a Geostrophic Adjustment Process
Stable atmosphere & terrain impede flow, alter force balance
Mass accumulation creates pressure ridge
Geostrophic, terrain-normal flow
Mass depletion west of barrier reinforces trough
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Climatological ResultsTotal Number of Events = 353
Cold Season Events = 180Warm Season Events = 173
• September -Highest frequency of events (?!!)
• July - lowest frequency of events
• Highest frequency of strong events in Winter months
• Lowest frequency of strong events in summer months (June - August)
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Classical (dry onset):• High > 1030 mb•>24 h duration•dry onset
Weak Onset•High < 1030•or < 24h duration•dry onset
Hybrid•High < 1030•or < 24h duration•precip. W/in 6h of onset
Southern Onset•high S of 40•dry onset
In-Situ
In-Situ
Classification based on location, strength of “parent high”:
Classical (Diab. Enh):• High > 1030 mb•>24 h duration•precip w/in 6-h of onset
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Classical (Diabatically Enhanced) T00 Peak Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
Classical (Diabatically Enhanced) T00 Onset Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
E-W Elongated High
Confluence with little or no ridging at 500mb
Cold front just off-shore
DIABATICALLY ENHANCED CLASSICAL(SYNOPTIC FORCING)
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Classical (Dry Onset) T00 Onset Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
Classical (Dry Onset) T00 Peak Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
N-S Elongated High
Confluence with more ridging at 500mb
Cold front far off-shore
DRY ONSET CLASSICAL(SYNOPTIC FORCING)
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Hybrid (HYBR) T00 Onset Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
In-Situ (INST) T00 Peak Centered
250-mb Geo. Ht., Isotachs
850-mb Geo. Ht., RH
500-mb Geo. Ht, Anomalies
SLP, anomalies
HYBRID CADEqual synoptic/diabatic processes
Weak and progressive high
IN-SITU CADDiabatic processes prevail
High in unfavorable location
Little or no CAA
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Surface P
lot
CONTAINS:* Mean Sea Level Pressure Isobars (mb)* 6-hour Total Precipitation (in)* 1000-500 mb Thickness (dm)
WHATDO YOU
LOOK FOR?
High Pressure ~1030mb in
New England
U-shaped Isobars east of Appalachians
546 line- Mix540 line-
Snow
Timing of Precip
(am/pm)
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850 mb P
lot
CONTAINS:* 850 mb Height (dm)* 850 mb Temperature (C)* 850 mb Winds (kts)
WHATDO YOU
LOOK FOR?
Southerly to easterly winds
Temperatures < 0C Snow< 3C Mix
Warm Air Intrusion
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700 mb P
lot
CONTAINS:* 700 mb Heights (dm)* Relative Humidity (%)* Omega (mb/s)
WHATDO YOU
LOOK FOR?
Relative Humidity
>70%
Negative Omegas Co-located with
RH
Dry Air Intrusion
Westerly Winds
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500 mb P
lot
WHATDO YOU
LOOK FOR?
Southwest Winds
Tilt of 500 mb Trough
Confluent Flow over
New England
CONTAINS:* 500 mb Heights (dm)* Absolute Vorticity (s^-1)* 500 mb Winds (kts)
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300 mb P
lot
WHATDO YOU
LOOK FOR?
Confluent Flow over
New England
Jet stream and streaks
Split Flow/ Dual Jet Structure
CONTAINS:* 300 mb Heights (dm)* 300 mb Isotachs (kts)* 300 mb Winds (kts)
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PRECIPITATION TYPE FORECASTING
FEBRUARY 5-6, 2004
Potential SC Ice Storm/CAD Event
(1)What is p-type?
(2)How do we make an educated guess?
(3)PUTTING THE METHOD TO USE…
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32 F 0C
COLD AIR DAMMING&
WINTER PRECIPITATION TYPES
Warm, moist air
COLD, DRY AIR
Rain Freezing Rain Sleet Snow
WARM WARM NOSENOSE
NORTHSOUTH
(1)
(2)
(3)
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PARTIAL THICKNESS AND GENERAL PARTIAL THICKNESS AND GENERAL FORECASTING RULESFORECASTING RULES
Partial thickness - the distance between intermediate levels in the atmosphere found in the model output, typically between 1000 and 500 millibars (i.e. 1000-850, 850-700, 700-500) that represent the thermal structure in the atmosphere with increasing height
TO DO ON-THE-FLY FORECASTING:TO DO ON-THE-FLY FORECASTING:
For snow to fall:
1000-850 THK < 1290m850-700 THK < 1540m
For sleet/freezing rain to fall:
850-700 THK 1540-1555m Sleet> 1555m Freezing Rain
(larger values of the 850-700 THK indicate warmer air aloft)
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5540 1575
3160 5790
Surface 850 mb
700 mb 500 mb
1000-500 THK
&
850 HEIGHT
700 HEIGHT
&
500 HEIGHT
????????????????
WILL IT BE……
SNOW, SLEET, OR
FREEZING RAIN
????????????????
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So for the Columbia Area in the Event from Thursday, Feb. 5th…
500mb 5790m
700mb 3160m
700-500 THK 2630m
700mb 3160m
850mb 1575m
850-700 THK 1585m
1000-500 THK 5540m
700-500 THK 2630m
850-700 THK 1585m
1000-850 THK 1325m
>1540m => no snow, warm nose present
>1300m => too warm to freeze
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•
P-TYPE FORECASTING NOMOGRAM
1325/1585
1000
-850
mb
TH
K
850-700mb THK
RAIN
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Actual Observations
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Related/Future Research
CAD Erosion (Stanton 2003, MS Thesis, NCSU)CAD Erosion (Stanton 2003, MS Thesis, NCSU)
High-resolution modeling (Caldwell 2004, MS Thesis, High-resolution modeling (Caldwell 2004, MS Thesis, NCSU)NCSU)
Coastal Frontogenesis (Appel 2002, MS Thesis, Coastal Frontogenesis (Appel 2002, MS Thesis, NCSU)NCSU)
Quantitative Precipitation Forecasting (QPF)Quantitative Precipitation Forecasting (QPF)