climatological conditions of lake-effect precipitation events...

Climatological Conditions of Lake-Effect Precipitation Events Associatedwith the New York State Finger Lakes

NEIL LAIRD

Department of Geoscience, Hobart and William Smith Colleges, Geneva, New York

RYAN SOBASH

School of Meteorology, University of Oklahoma, Norman, Oklahoma

NATASHA HODAS

Department of Environmental Science, Rutgers, The State University of New Jersey, New Brunswick, New Jersey

(Manuscript received 4 June 2009, in final form 11 January 2010)

ABSTRACT

A climatological analysis was conducted of the environmental and atmospheric conditions that occurred

during 125 identified lake-effect (LE) precipitation events in the New York State Finger Lakes region for the

11 winters (October–March) from 1995/96 through 2005/06. The results complement findings from an earlier

study reporting on the frequency and temporal characteristics of Finger Lakes LE events that occurred as

1) isolated precipitation bands over and downwind of a lake (NYSFL events), 2) an enhancement of LE

precipitation originating from Lake Ontario (LOenh events), 3) an LE precipitation band embedded within

widespread synoptic precipitation (SYNOP events), or 4) a transition from one type to another. In com-

parison with SYNOP and LOenh events, NYSFL events developed with the 1) coldest temperatures,

2) largest lake–air temperature differences, 3) weakest wind speeds, 4) highest sea level pressure, and 5) lowest

height of the stable-layer base. Several significant differences in conditions were found when only one or both

of Cayuga and Seneca Lakes, the largest Finger Lakes, had LE precipitation as compared with when the

smaller Finger Lakes also produced LE precipitation. In addition, transitional events containing an NYSFL

time period occurred in association with significantly colder and drier air masses, larger lake–air temperature

differences, and a less stable and shallower boundary layer in comparison with those associated with solitary

NYSFL events.

1. Introduction

Investigations of lake-effect (LE) snowstorms and the

conditions leading to their development have typically

focused on events associated with the North American

Great Lakes. Numerous investigations have presented LE

case studies (e.g., Braham 1983; Schmidlin and Kosarik

1999; Lackmann 2001), discussed issues related to fore-

casting LE snowstorms (e.g., Niziol 1987; Burrows 1991;

Niziol et al. 1995; Ellis and Leathers 1996), and conducted

mesoscale model simulations toward understanding the

atmospheric conditions favorable for LE snowfall (e.g.,

Lavoie 1972; Hjelmfelt 1990; Laird et al. 2003a,b). In

addition, several studies have investigated historic snow-

fall trends in the Great Lakes region (e.g., Braham and

Dungey 1984; Norton and Bolsenga 1993; Burnett et al.

2003; Ellis and Johnson 2004) and studied cloud and pre-

cipitation development in association with LE systems

(e.g., Agee and Gilbert 1989; Braham 1990; Braham et al.

1992; Kristovich and Braham 1998; Schroeder et al. 2006).

Few studies have investigated LE precipitation events

associated with lakes smaller than the Great Lakes (e.g.,

Steenburgh and Onton 2001; Cairns et al. 2001; Schultz

et al. 2004; Payer et al. 2007) and fewer have conducted

climatological analyses of LE events over small lakes

(Carpenter 1993; Steenburgh et al. 2000; Laird et al.

2009a,b). Carpenter (1993) and Steenburgh et al. (2000)

studied the characteristics of LE snowstorms associ-

ated with the Great Salt Lake for the winters of

Corresponding author address: Neil F. Laird, Dept. of Geo-

science, Hobart and William Smith Colleges, 300 Pulteney St.,

Geneva, NY 14456.

E-mail: [email protected]

1052 J O U R N A L O F A P P L I E D M E T E O R O L O G Y A N D C L I M A T O L O G Y VOLUME 49

DOI: 10.1175/2010JAMC2312.1

� 2010 American Meteorological Society

1970/71–1987/88 and 1994/95–1997/98, respectively. These

two studies along with investigations by Steenburgh and

Onton (2001) and Onton and Steenburgh (2001) have

greatly increased awareness and understanding of Great

Salt Lake LE events. Laird et al. (2009a) more recently

conducted a climatological study examining the fre-

quency, timing, and environmental conditions of LE

precipitation events associated with Lake Champlain

for the nine-winter period from 1997/98 through 2005/06.

They found that Lake Champlain LE events occurred

within a limited range of wind and temperature condi-

tions, thereby producing events that are susceptible to

small changes in environmental conditions.

Laird et al. (2009b, hereinafter referred to as LSH09)

presented the frequency and temporal characteristics (i.e.,

duration and timing) of LE events that originated over

or were enhanced by the New York State (NYS) Finger

Lakes during an 11-winter period from 1995/96 through

2005/06. LSH09 found that Finger Lakes LE events occur

as 1) a well-defined, isolated LE precipitation band over

and downwind of a lake (NYSFL events), 2) an enhance-

ment of mesoscale LE precipitation originating from Lake

Ontario and extending southward over an individual

Finger Lake (LOenh events), 3) a quasi-stationary meso-

scale precipitation band positioned over a lake embedded

within extensive regional precipitation from a synoptic

weather system (SYNOP events), or 4) a transition from

one type to another. They found that the frequency of

LE events in the Finger Lakes region contains a large

amount of interannual and intraseasonal variability (Fig. 1),

suggesting that different climatic patterns have consid-

erable influence on the occurrence of these small-lake LE

events.

The current study builds on the understanding of LE

events in the NYS Finger Lakes region by presenting

climatological analyses of their environmental and atmo-

spheric conditions. The material presented in this study

provides a contribution to the general understanding of

LE events and the different mesoscale environments in

which small-lake LE events form. Even though Great

Lakes LE events typically receive much larger snowfall

totals than these small-lake LE events, which often pro-

vide 3–8 in. (1 in. ’ 2.54 cm) of snowfall, understandingthe conditions that favor the development of LE pre-

cipitation events associated with small lakes will assist

in improving their prediction. For example, Environ-

ment Canada has expressed increased concern about

the need for better understanding and prediction of LE

snow squalls associated with small lakes throughout the

Canadian provinces of Ontario and Quebec (R. Tabory,

Ontario Storm Prediction Centre, Environment Canada,

2009, personal communication). The Finger Lakes pro-

vide drinking water for nearly 700 000 residents (Callinan

2001), and, although studies have not yet quantified the

significance of NYS Finger Lakes LE events to the local

hydrological contributions in the region, winter precipita-

tion patterns in western NYS show a regional enhance-

ment of seasonal precipitation downstream (i.e., southeast)

of the Finger Lakes (Fig. 2).

The methods and data used in the study, including an

overview of the criteria for identifying several types of

NYS Finger Lakes LE events, are described in section 2.

A more complete description of the method used to

identify LE events is provided in LSH09. Section 3

presents the results of the climatological analyses. A

concluding discussion and summary are provided in

section 4.

2. Finger Lakes region, analysis methods, and data

a. Finger Lakes region

The Finger Lakes region within central NYS includes

11 lakes of varying sizes and orientations (Fig. 3). The

largest two lakes, Seneca and Cayuga, are narrow (widths

of ,5 km) and have lengths of nearly 61 and 64 km, re-spectively. The six easternmost Finger Lakes, those ex-

amined in this investigation, range in surface area from

7.6 km2 (Otisco Lake) to 175 km2 (Seneca Lake). These

lakes are considerably smaller than Lake Champlain

(1127 km2), the Great Salt Lake (4400 km2), and Lake

Ontario (18 960 km2), the smallest of the Great Lakes.

Lake Ontario is approximately 50 km north of the Fin-

ger Lakes, and the topographic elevation increases from

the northern to southern portion of the glacially pro-

duced region (Fig. 3).

FIG. 1. Intraseasonal and interannual frequency plot of lake-effect

events for the winters from 1995/96 to 2005/06.

MAY 2010 N O T E S A N D C O R R E S P O N D E N C E 1053

b. Identification of NYS Finger Lakes LE

Assessment of the Weather Surveillance Radar-1988

Doppler (WSR-88D) level-II and level-III data resulted

in the identification of 125 events during the 11-wintertime

period for which one or more of the NYS Finger Lakes

had LE precipitation associated with them (LSH09). Sev-

eral indicators, similar to those applied by Laird et al.

(2009a) for Lake Champlain LE events, were used to

establish a justified and repeatable method for identi-

fication of Finger Lakes LE precipitation based solely

on the radar data. The method used to identify events

and examples of each NYS Finger Lakes LE classifi-

cation are provided in LSH09. The three indicators used

to identify LE events included 1) the existence of co-

herent precipitation in the radar reflectivity field that

developed or was enhanced over an individual lake and

remained quasi stationary, 2) precipitation that was com-

posed of mesoscale structural features that were clearly

distinguishable from extensive or transitory regions of

precipitation, and 3) precipitation that often demon-

strated increasing reflectivity, depth, or spatial coverage

at locations along the downwind extent of the mesoscale

band.

c. Datasets

The hourly surface observations from four stations

in and around the NYS Finger Lakes region were used

FIG. 2. Average winter (December–February) liquid water

equivalent precipitation (mm) over northern and western NYS.

The map displays county boundaries, and the shaded region de-

notes the Finger Lakes region shown in Fig. 3 (based on Fig. 1a

from Scott and Huff 1996).

FIG. 3. Regional topographic map of NYS Finger Lakes region (includes lake names, KBGM

radar location and range rings, and sites of several reference cities). The six eastern Finger

Lakes included in this study are shaded gray. Dashed lines represent lines of constant elevation

(183, 274, and 366 m). HWS indicates the Hobart and William Smith Colleges site.


in this study (Fig. 3). Hourly surface data from three

Automated Surface Observing Systems (ASOS) located

at Syracuse (SYR), Rochester (ROC), and Penn Yan

(PEO), New York, were retrieved from the National

Climatic Data Center Global Surface Hourly database.

The SYR and ROC sites recorded hourly measurements

of air temperature, dewpoint temperature, wind direction,

wind speed, and sea level pressure (SLP) throughout

the 11-winter period (1995/96–2005/06). The PEO sta-

tion was relocated and converted to ASOS operation in

January of 1998. For all stations, only the full aviation

routine weather report (METAR) observations taken

on or near the top of the hour were selected; no special

observations (SPECI) were used. In addition to the three

ASOS stations, hourly data from the Game Farm Road

Weather Station in Ithaca, New York (the site defined for

this study as ITH), were obtained from the Northeast

Regional Climate Center. The onset and dissipation times

of LE events were identified using Binghamton, New

York (KBGM), WSR-88D radar data, and all hourly

surface observations within these event times were used

in the analysis presented. Therefore, these hourly obser-

vations represent a range of conditions from start to end

of events of similar character (i.e., SYNOP, LOenh, and

NYSFL) that achieve an array of intensities, have dif-

fering evolutions and durations, and provide information

regarding the bounds necessary to support LE de-

velopment in the NYS Finger Lakes region.

Routine (hourly or daily) water temperature mea-

surements in the Finger Lakes, especially in the winter,

are typically unavailable, thereby providing a challenge

in examining the thermal forcing conducive to LE pre-

cipitation events in the region. In November 2006, the

Department of Geoscience at Hobart and William Smith

Colleges began measuring and archiving Seneca Lake

water temperatures. Seneca Lake has a maximum (av-

erage) depth of 188 (89) m and typically remains without

extensive ice cover during the entire winter. Water tem-

perature measurements are collected 2 times per day in

the northwestern portion of Seneca Lake (42851.439N,76858.819W) at an approximate depth of 2 m (Fig. 3).These measurements have provided a continuous record

of upper-epilimnion (i.e., the top layer of water directly

affected by air temperature and wind) water temperature

for three cold seasons (2006/07, 2007/08, and 2008/09).

In the absence of a longer record of Finger Lakes water

temperatures, the daily mean water temperature was

used in conjunction with the surface meteorological ob-

servations from SYR, ROC, PEO, and ITH for Finger

Lakes LE events from 1995/96 through 2005/06 to esti-

mate environmental conditions. Seneca Lake mean daily

water temperatures range from 188C in early October tonear 38C in late January and early February (Fig. 4). For

reference, the 30-yr (1976–2005) mean daily air temper-

ature at SYR ranges from 158C in early October to about278C in the later part of January. The mean Seneca Lakewater temperature remains warmer than the mean SYR

air temperature for almost the entire winter (October–

March), except during the last few days in March.

National Weather Service upper-air soundings col-

lected at Buffalo, New York (KBUF), during Finger

Lakes LE events were retrieved from the University of

Wyoming online archive (http://www.weather.uwyo.edu/

upperair/sounding.html). Although the KBUF sounding

site is approximately 150 km west of the eastern Finger

Lakes, these measurements provide vertical atmospheric

profiles that are the most representative of an air mass

modified by Lake Ontario under typical northerly wind

conditions that occur during LE events in the Finger Lakes

region. A total of 92 soundings occurred during events

(16 for SYNOP, 45 for LOenh, and 31 for NYSFL).

The North American Regional Reanalysis (NARR;

Mesinger et al. 2006) was used to examine large-scale

composite atmospheric patterns using the National Oce-

anic and Atmospheric Administration Earth System Re-

search Laboratory (NOAA/ESRL) Physical Science

Division online utilities at the Climate Diagnostics Cen-

ter (http://www.cdc.noaa.gov). Composite analyses of

SYNOP, LOenh, and NYSFL events were composed of

3-h NARR output parameters available between the

start and end times of identified events. The SYNOP,

FIG. 4. Seneca Lake water temperatures (8C) for winters of2006/07, 2007/08, and 2008/09. The heavy black solid line rep-

resents daily mean water temperature, and the heavy black

dashed line represents the normal (1976–2005) SYR daily air

temperature.


LOenh, and NYSFL composite analyses were produced

from 38, 80, and 70 NARR time periods, respectively.

3. Results

A total of 125 LE events were identified using KBGM

radar data for the winters of 1995/96–2005/06 (see ap-

pendix in LSH09). The LE event types consisted of

36 NYSFL, 57 LOenh, 15 SYNOP, and 17 transitional

events. Hourly observations during transitional events

were identified as being associated with NYSFL, LOenh,

or SYNOP time periods and were included in the ap-

propriate event analyses. Analyses of conditions during

NYSFL, LOenh, and SYNOP events used hourly sur-

face observations from 381, 638, and 211 time periods,

respectively. Statistical comparative analyses were con-

ducted with a two-independent-samples nonparametric

test (Mann–Whitney U test), which does not assume data

are normally distributed or have equal variance and uses

a critical Z value of 1.96 (p # 0.05) to measure for sig-

nificant differences. The results presented in this section

provide information on the environmental conditions for

SYNOP, NYSFL, and LOenh events, variations in envi-

ronmental conditions based on lake size, and comparison

of transitional and solitary LE events.

a. Environmental conditions for SYNOP, NYSFL,and LOenh events

1) SYNOPTIC COMPOSITES

The NYSFL NARR composite analyses (Figs. 5a–c)

show 1) a region of below-freezing temperatures ex-

tending southward across the eastern United States with

temperatures of approximately 288C over the FingerLakes region, 2) low pressure along the New England

coastline and high pressure located across the western

Great Lakes with northwest surface winds over the

Finger Lakes region, and 3) a north-northwesterly-

oriented height pattern and winds at 850 hPa. Com-

posite atmospheric patterns for SYNOP and LOenh

events were not significantly different than those for

NYSFL events. Areas of low and high sea level pres-

sure were located farther westward for LOenh and

SYNOP events, respectively. Surface and 850-hPa tem-

peratures in the Finger Lakes region from the NARR

composites were warmer for both LOenh and SYNOP

events, with surface temperatures of approximately 248and 268C, respectively.

2) SURFACE CONDITIONS

Notable temperature variations were found between

SYNOP, LOenh, and NYSFL event types using the

surface station hourly observations (Fig. 6). The four-

station group-mean temperatures for SYNOP, LOenh,

FIG. 5. NARR composite (a) 2-m surface temperature, (b) SLP

and 2-m wind, and (c) 850-hPa height and wind for NYSFL events.

Isotherms, isobars, and isohypses are plotted using intervals of 38C,2 hPa, and 15 m, respectively. The black circle shows the location

of the eastern Finger Lakes region. The composite maps were

generated using the NOAA/ESRL Physical Sciences Division Web

site (http://www.cdc.noaa.gov/).


and NYSFL are 26.68, 25.98, and 210.58C, respectively.Statistical analysis established that temperatures for

SYNOP, LOenh, and NYSFL all differed significantly.

LSH09 showed that the different event types are well

distributed across all months analyzed (i.e., each type

of event occurs in each month of October–March).

The statistical differences in temperatures were found

to be associated with conditions during differing event

type and not to be attributable to a systematic differ-

ence in seasonality of event type. Significant temper-

ature variations were not found across the different

surface stations for most LE event types (Fig. 6). ROC

temperatures were typically the warmest of all stations.

For example, the ROC mean temperature during LOenh

events was 25.48C as compared with 26.08, 26.18, and26.08C at SYR, PEO, and ITH, respectively. SYR tem-peratures were significantly colder than at the other sta-

tions during NYSFL events. The mean temperatures at

SYR, ITH, PEO, and ROC for NYSFL events were

211.38, 210.48, 210.08, and 210.08C, respectively.Surface temperatures were above freezing for 12.0%

of all observations during events, and 16.2% of events

had an event-average air temperature above 08C (Fig. 6).This result is much different from temperature conditions

during Lake Champlain LE events, which very rarely

(1 of 67 events identified during nine winters) had tem-

peratures above 08C (Laird et al. 2009a). This suggeststhat NYS Finger Lakes precipitation bands resulted in

both LE snow and rain and that some events likely only

produced LE rainfall. In addition, approximately 50% of

LE events with an event-average air temperature above

08C occurred during October. These results are similar tofindings from a study by Miner and Fritsch (1997), which

used data from seven autumns (September–November for

1988–94) to investigate LE precipitation in the vicinity of

Lake Erie. They found that LE precipitation (i.e., snow

and rain) occurred during approximately 20% of days in

September–November of each year, with the largest num-

ber of events in October, most of which produced LE rain.

Hourly air temperatures measured at all stations were

used with Seneca Lake daily mean water temperatures

to estimate the surface lake–air temperature difference

DT for each hour during events (Fig. 7). The mean DTfor SYNOP, LOenh, and NYSFL events was 11.68, 11.68,and 14.28C, respectively. Measurements of DT for NYSFLwere found to be statistically different than during

SYNOP and LOenh events. Surface DT values for LEevents in the Finger Lakes region (DTmean 5 12.48C)were smaller than those that Laird et al. (2009a) found

for Lake Champlain LE events (DTmean 5 16.78C). Forboth regions, DT values were substantially larger thanthose observed during LE events on the Great Salt

Lake, which had mean and maximum DT values of 7.68and 14.28C, respectively (Steenburgh et al. 2000).

Dewpoint temperatures were similar during SYNOP

and LOenh events, whereas NYSFL events had statis-

tically lower values. The mean dewpoint temperatures

for SYNOP, LOenh, and NYSFL events were 29.18,

FIG. 6. Distributions of temperature (8C) at four surface sites(ITH, PEO, ROC, and SYR) for (a) SYNOP, (b) LOenh, and (c)

NYSFL events. Asterisks represent extreme values, and open cir-

cles represent outliers.

FIG. 7. As in Fig. 6, but for temperature difference between

average Seneca Lake water temperature and surface air tempera-

ture (DT ).


29.18, and 213.48C, respectively. The dewpoint tem-peratures for LE events in the Finger Lakes region were

significantly higher than those found to occur during

Lake Champlain LE events (Laird et al. 2009a). Both the

warmer temperatures and greater amount of atmospheric

moisture measured during Finger Lakes LE events are

undoubtedly a result of the upwind influence of Lake

Ontario and the significant modification to polar air

masses by the lake through positive (upward directed)

sensible and latent heat fluxes.

The average SLP increased across SYNOP (1014.9 hPa),

LOenh (1020.7 hPa), and NYSFL (1024.9 hPa) events

(Fig. 8). The differences among all event types were

statistically significant. This finding is consistent with

the observed eastward shift of the SLP pattern from the

NARR composites for SYNOP, LOenh, and NYSFL

events, where SYNOP events occur in the closest prox-

imity to an area of low pressure. These variations in SLP

with LE event type were also associated with differences

in SLP distributions that had an impact on wind speeds.

NYSFL events occurred under the weakest surface wind

conditions during any of the three types of LE events

(Fig. 9). The four-station group-mean wind speed during

NYSFL was 3.9 m s21, whereas LOenh and SYNOP

events had mean wind speeds of 4.5 and 4.9 m s21, re-

spectively. Wind speeds during NYSFL were found to be

statistically different than conditions that occurred during

SYNOP and LOenh events. Wind directions were similar

regardless of observing station or LE event type. In

general, wind directions were from the northwest, with

the median values ranging between 3108 and 3208.

Few calm wind observations were reported during LE

events. Frequency analyses of hourly observations from

all stations showed that 3.5% reported calm conditions

and 7.8% had measurements of wind speed of less than

2 m s21. The wind speed conditions during Finger Lakes

LE events were considerably different than conditions

that occurred during Lake Champlain LE events, where

hourly observations from stations within the Lake Cham-

plain Valley showed that 12.5% and 21.3% had calm

winds and wind speeds of less than 2 m s21, respectively.

3) SOUNDINGS

Rothrock (1969) and Niziol (1987) found that during

Great Lakes LE snowstorms a lapse rate of at least the

dry adiabatic lapse rate from the surface to 850 hPa (i.e.,

a difference in temperature between the lake surface

and 850 hPa DT850 of $138C) was a necessary criterionfor storm development. For Finger Lakes LE events,

DT850 was determined using soundings from KBUF andSeneca Lake mean water temperatures. Approximately

88% of DT850 values obtained during Finger Lakes eventsexceeded the condition of 138C. The average and vari-ability of DT850 values was largest (smallest) for NYSFL(SYNOP) events (Fig. 10a). The mean DT850 values forSYNOP, LOenh, and NYSFL events were 18.68, 18.88, and19.28C, respectively. These values are consistent with themean DT850 values found for Lake Champlain LE events,which ranged from 16.08 to 18.78C (Laird et al. 2009a).

Approximately 93% of the 92 KBUF soundings col-

lected during LE in the Finger Lakes region had a stable

layer present in the lower troposphere. The base of

FIG. 8. As in Fig. 6, but for distributions of SLP (hPa) at three

surface sites (PEO, ROC, and SYR).FIG. 9. As in Fig. 6, but for wind speed (m s21).


a stable layer was defined as the height at which the

environmental lapse rate became less than the moist

adiabatic lapse rate. In most cases, the stable layer was

characterized as having a temperature inversion. The

stable layer was elevated above the surface, with a con-

vective mixed layer existing in all but six soundings

(6.5%). Figure 10b shows that the mean height of the

stable-layer base during NYSFL events was significantly

lower (1.2 km) when statistically compared with LOenh

and SYNOP events (1.5 km). The lower stable-layer

base and presence of only Finger Lakes precipitation

bands during NYSFL events suggest that the precondi-

tioned boundary layer coming southward from Lake

Ontario was significantly reduced in depth and limited in

ability to support LE precipitation development down-

wind of Lake Ontario without the supplementary con-

tribution of latent and sensible fluxes from individual

Finger Lakes.

Similar to surface wind speeds, 850-hPa wind speeds

were weakest for NYSFL events (mean 5 10.4 m s21)and increased for LOenh (11.2 m s21) and SYNOP

(12.9 m s21) events. The 850-hPa wind directions con-

tained a larger northerly wind component than did the

surface observations. However, the vertical directional

shear from the surface to 850 hPa was typically small for

NYSFL, LOenh, and SYNOP events, with median values

of 288, 168, and 208 km21, respectively. The small amountof directional shear is a necessary criterion suggested by

Niziol et al. (1995) for favoring LE snowband develop-

ment in the Great Lakes region.

b. Variations based on lake size

LSH09 found that LE precipitation events occurred

in association with each of the six easternmost Finger

Lakes. Cayuga and Seneca Lakes, the two largest lakes,

had the highest frequency of events—82% and 96% of

the 125 identified events, respectively. The smaller four

lakes, Keuka (surface area of 47.0 km2), Otisco (7.6 km2),

Owasco (26.7 km2), and Skaneateles (36.0 km2), had

LE precipitation during 22%, 30%, 50%, and 64% of

events, respectively. The lower frequency of identified LE

events for Keuka Lake demonstrates that the northeast–

southwest orientation of the lake major axis played a lim-

iting role in the development of LE.

Several statistically significant differences in condi-

tions were found when only one or both of Cayuga and

Seneca Lakes had LE precipitation as compared with

when the smaller Finger Lakes also produced LE pre-

cipitation. When LE precipitation developed in associ-

ation with the smaller Finger Lakes across the same type

of LE event, 1) temperatures were colder and DT valueswere larger, 2) dewpoint temperatures were higher, and

3) wind speeds were larger for both SYNOP and NYSFL

events and smaller for LOenh events. Wind directions

were more frequently from the northwest when LE

precipitation developed in association with the smaller

Finger Lakes as compared with more northerly wind

directions when LE precipitation developed only in as-

sociation with one or both of the larger Finger Lakes.

c. Comparison of transitional and solitary LE events

Both the surface SLP observations and NARR com-

posite analyses suggest a sequential nature to the oc-

currence of the three LE event types identified for the

Finger Lakes region (SYNOP, LOenh, and NYSFL).

This result is similar to the finding of Ellis and Leathers

(1996) that identified five synoptic patterns that were

associated with Great Lakes LE snowfall in western New

York and northwestern Pennsylvania from Lakes Ontario

and Erie. Many of the identified events in the Finger

Lakes region occurred as a solitary type; however, nearly

14% occurred as transitional cases. The transitional cases

that occurred were SYNOP to LOenh (one event),

LOenh to NYSFL (nine events), and SYNOP to NYSFL

(seven events). The sequential ordering of LE event type

during these transitional cases provides support that

there is an evolutionary nature in the synoptic-scale

pattern and boundary layer structure for different types

of LE events. Only NYSFL solitary events and transi-

tional events containing an NYSFL time period were

examined since so few transitional events containing a

LOenh time period were identified. The differences

between several environmental variables for these two

FIG. 10. Distribution of (a) temperature difference between lake

and 850-hPa level and (b) height of the base of an existing stable

layer located in KBUF soundings for each lake-effect event type.


NYSFL event groups are presented in Table 1. Transi-

tional events containing an NYSFL time period occurred

with significantly colder and drier air masses, larger lake–

air temperature differences, and a less stable and shal-

lower boundary layer when compared with solitary

NYSFL events.

4. Discussion and summary

Similar to the small variation in temperatures and

winds observed for Lake Champlain LE events (Laird

et al. 2009a), Finger Lakes LE events occur under a

constricted range of conditions and suggest they are

likely susceptible to slight shifts in the magnitude and

frequency of cold-air outbreaks (e.g., Walsh et al. 2001;

Portis et al. 2006). For example, the monthly variability

of DT and event duration for all Finger Lakes LE eventsis shown in Figs. 11a and 11b. Although a fairly large

range in event duration exists within each month, a

general seasonal relationship is evident where smaller

DT values correspond to shorter events, especially in theearly winter, and larger DT values are linked to longer-lasting events, principally in January. Further investigation

of these temporal relationships would allow for greater

understanding of the connection between mesoscale sys-

tems and climate variability, as well as for comparative

analyses of necessary conditions for the development and

change in frequency of Finger Lakes events versus those

associated with lakes across a range of locations and sizes

(e.g., Lake Champlain, Great Salt Lake, and Great Lakes).

Because of the close proximity of the Finger Lakes to

the southern shore of Lake Ontario, LE processes and

mesoscale circulations originating over Lake Ontario

often contribute directly to the development of LE

precipitation over the Finger Lakes. This leads to warmer

air temperatures, greater amounts of atmospheric mois-

ture, and higher LE event frequency of Finger Lakes

LE events when compared with the colder and drier

climatological conditions and lower frequency of Lake

Champlain LE events, which develop in a region without

a large water body located in close upwind proximity. The

authors acknowledge that Lake Ontario is contributing to

the development of NYSFL events; however, this linkage

is difficult to quantify without specialized measurements

beyond the climatological and operational datasets cur-

rently available. Cosgrove et al. (1996) used a simple

mesoscale model to complete several preliminary simu-

lations of a Finger Lakes LE event (11 December 1993)

and suggested that Seneca and Cayuga Lakes were able

TABLE 1. Mean environmental conditions for solitary and tran-

sitional NYSFL events. Variables include lake–air temperature

difference DT and lake–850-hPa temperature difference DT850.

Variable

Solitary

NYSFL

Transitional

NYSFL

Surface temperature (8C) 29.2 213.1Dewpoint temperature (8C) 212.1 216.2DT (8C) 13.4 16.1DT850 (8C) 18.8 20.1Surface wind speed (m s21) 3.8 4.0

850-hPa wind speed (m s21) 10.3 10.6

Stable-layer base height (m) 1283 917

FIG. 11. Monthly variability in (a) temperature difference DTand (b) event duration for each lake-effect event type. The hori-

zontal reference line in (b) shows the mean event duration (9.4 h)

for Finger Lakes LE events.


to support LE snow without the upstream presence of

Lake Ontario but that the smaller Finger Lakes were

only able to support an enhancement to LE snow origi-

nating over Lake Ontario. The use of special atmospheric

observations from strategically placed field facilities, such

as boundary layer profilers and atmospheric sounding

systems, along with more comprehensive mesoscale model

simulations, would be required to understand and quantify

the influence of Lake Ontario boundary layer processes

and mesoscale circulations on the development and fre-

quency of Finger Lakes LE events.

This study provides a climatological analysis of the

environmental and atmospheric conditions that occurred

during 125 identified LE precipitation events in the New

York State Finger Lakes region for 11 winters. The

results complement findings from LSH09, that reported

on the frequency and temporal characteristics of Finger

Lakes LE events. An examination of climatological con-

ditions during Finger Lakes LE events provides several

unique findings. NYSFL events developed with the 1)

coldest temperatures, 2) largest lake–air temperature

differences, 3) weakest wind speeds, 4) highest sea level

pressure, and 5) lowest height of the stable-layer base.

Soundings collected during events showed that approxi-

mately 88% of DT850 values exceeded the establishedcriteria of 138C and had a mean DT850 value of 18.98C.In addition, the base of a stable layer during NYSFL

events was found exclusively below 2.1 km and the

mean height was substantially lower than for LOenh

and SYNOP events.

Several significant differences in conditions were

found when only one or both of Cayuga and Seneca

Lakes, the largest Finger Lakes, had LE precipitation

as compared with when the smaller Finger Lakes also

produced LE precipitation. Last, transitional events con-

taining an NYSFL time period occurred in association

with significantly colder and drier air masses, larger lake–

air temperature differences, and a less stable and shal-

lower boundary layer when compared with those of

solitary NYSFL events.

Acknowledgments. The second and third authors con-

ducted this research during the 2005 and 2006 summer

undergraduate research program at Hobart and William

Smith Colleges. Helpful comments from Michael Evans

and Michael Jurewicz of the Binghamton, New York,

National Weather Service Forecast Office and David

Kristovich of the Illinois State Water Survey greatly

aided this investigation. We appreciate assistance from

the Northeast Regional Climate Center and National

Climatic Data Center in obtaining the data necessary for

this project. This research was supported by the National

Science Foundation under Grants ATM 02-02305 and

ATM 05-12233. We gratefully acknowledge support by

the Office of the Provost at Hobart and William Smith

Colleges. Any opinions, findings, conclusions, and rec-

ommendations expressed in this publication are those of

the authors and do not necessarily reflect the views of the

National Science Foundation.

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