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

1052 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

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 comparison 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 Lavoie 1972; Hjelmfelt 1990; Laird et al. 2003a,b). In addition, several studies have investigated historic snow- Investigations of lake-effect (LE) snowstorms and the fall trends in the Great Lakes region (e.g., Braham and conditions leading to their development have typically Dungey 1984; Norton and Bolsenga 1993; Burnett et al. focused on events associated with the North American 2003; Ellis and Johnson 2004) and studied cloud and pre- Great Lakes. Numerous investigations have presented LE cipitation development in association with LE systems case studies (e.g., Braham 1983; Schmidlin and Kosarik (e.g., Agee and Gilbert 1989; Braham 1990; Braham et al. 1999; Lackmann 2001), discussed issues related to fore- 1992; Kristovich and Braham 1998; Schroeder et al. 2006). casting LE snowstorms (e.g., Niziol 1987; Burrows 1991; Few studies have investigated LE precipitation events Niziol et al. 1995; Ellis and Leathers 1996), and conducted associated with lakes smaller than the Great Lakes (e.g., mesoscale model simulations toward understanding the Steenburgh and Onton 2001; Cairns et al. 2001; Schultz atmospheric conditions favorable for LE snowfall (e.g., 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. Corresponding author address: Neil F. Laird, Dept. of Geo- science, Hobart and William Smith Colleges, 300 Pulteney St., 2009a,b). Carpenter (1993) and Steenburgh et al. (2000) Geneva, NY 14456. studied the characteristics of LE snowstorms associ- E-mail: [email protected] ated with the Great Salt Lake for the winters of

DOI: 10.1175/2010JAMC2312.1

Ó 2010 American Meteorological Society 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

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 frequency, 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 conditions, 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 FIG. 1. Intraseasonal and interannual frequency plot of lake-effect 2005/06. LSH09 found that Finger Lakes LE events occur events for the winters from 1995/96 to 2005/06. as 1) a well-defined, isolated LE precipitation band over and downwind of a lake (NYSFL events), 2) an enhance- 2001), and, although studies have not yet quantified the ment of mesoscale LE precipitation originating from Lake significance of NYS Finger Lakes LE events to the local Ontario and extending southward over an individual hydrological contributions in the region, winter precipita- Finger Lake (LOenh events), 3) a quasi-stationary meso- tion patterns in western NYS show a regional enhance- scale precipitation band positioned over a lake embedded ment of seasonal precipitation downstream (i.e., southeast) within extensive regional precipitation from a synoptic of the Finger Lakes (Fig. 2). weather system (SYNOP events), or 4) a transition from The methods and data used in the study, including an one type to another. They found that the frequency of overview of the criteria for identifying several types of LE events in the Finger Lakes region contains a large NYS Finger Lakes LE events, are described in section 2. amount of interannual and intraseasonal variability (Fig. 1), A more complete description of the method used to suggesting that different climatic patterns have consid- identify LE events is provided in LSH09. Section 3 erable influence on the occurrence of these small-lake LE presents the results of the climatological analyses. A events. concluding discussion and summary are provided in The current study builds on the understanding of LE section 4. events in the NYS Finger Lakes region by presenting climatological analyses of their environmental and atmospheric conditions. The material presented in this study 2. Finger Lakes region, analysis methods, and data provides a contribution to the general understanding of a. Finger Lakes region LE events and the different mesoscale environments in which small-lake LE events form. Even though Great The Finger Lakes region within central NYS includes Lakes LE events typically receive much larger snowfall 11 lakes of varying sizes and orientations (Fig. 3). The totals than these small-lake LE events, which often pro- largest two lakes, Seneca and Cayuga, are narrow (widths vide 3–8 in. (1 in. ’ 2.54 cm) of snowfall, understanding of ,5 km) and have lengths of nearly 61 and 64 km, re- the conditions that favor the development of LE pre- spectively. The six easternmost Finger Lakes, those ex- cipitation events associated with small lakes will assist amined in this investigation, range in surface area from in improving their prediction. For example, Environ- 7.6 km2 (Otisco Lake) to 175 km2 (Seneca Lake). These ment Canada has expressed increased concern about lakes are considerably smaller than Lake Champlain the need for better understanding and prediction of LE (1127 km2), the Great Salt Lake (4400 km2), and Lake snow squalls associated with small lakes throughout the Ontario (18 960 km2), the smallest of the Great Lakes. Canadian provinces of Ontario and Quebec (R. Tabory, Lake Ontario is approximately 50 km north of the Fin- Ontario Storm Prediction Centre, Environment Canada, ger Lakes, and the topographic elevation increases from 2009, personal communication). The Finger Lakes pro- the northern to southern portion of the glacially provide drinking water for nearly 700 000 residents (Callinan duced region (Fig. 3). 1054 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

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 identification 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 composed of mesoscale structural features that were clearly FIG. 2. Average winter (December–February) liquid water distinguishable from extensive or transitory regions of equivalent precipitation (mm) over northern and western NYS. The map displays county boundaries, and the shaded region de- precipitation, and 3) precipitation that often demon- notes the Finger Lakes region shown in Fig. 3 (based on Fig. 1a strated increasing reflectivity, depth, or spatial coverage from Scott and Huff 1996). at locations along the downwind extent of the mesoscale band. b. Identification of NYS Finger Lakes LE c. Datasets Assessment of the Weather Surveillance Radar-1988 The hourly surface observations from four stations Doppler (WSR-88D) level-II and level-III data resulted in and around the NYS Finger Lakes region were used

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. MAY 2010 N O T E S A N D C O R R E S P O N D E N C E 1055 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 station 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 FIG. 4. Seneca Lake water temperatures (8C) for winters of surface observations within these event times were used 2006/07, 2007/08, and 2008/09. The heavy black solid line rep- in the analysis presented. Therefore, these hourly obser- resents daily mean water temperature, and the heavy black vations represent a range of conditions from start to end dashed line represents the normal (1976–2005) SYR daily air temperature. of events of similar character (i.e., SYNOP, LOenh, and NYSFL) that achieve an array of intensities, have differing evolutions and durations, and provide information reference, the 30-yr (1976–2005) mean daily air temper- regarding the bounds necessary to support LE de- ature at SYR ranges from 158C in early October to about velopment in the NYS Finger Lakes region. 278C in the later part of January. The mean Seneca Lake Routine (hourly or daily) water temperature mea- water temperature remains warmer than the mean SYR surements in the Finger Lakes, especially in the winter, air temperature for almost the entire winter (October– are typically unavailable, thereby providing a challenge March), except during the last few days in March. in examining the thermal forcing conducive to LE pre- National Weather Service upper-air soundings col- cipitation events in the region. In November 2006, the lected at Buffalo, New York (KBUF), during Finger Department of Geoscience at Hobart and William Smith Lakes LE events were retrieved from the University of Colleges began measuring and archiving Seneca Lake Wyoming online archive (http://www.weather.uwyo.edu/ water temperatures. Seneca Lake has a maximum (av- upperair/sounding.html). Although the KBUF sounding erage) depth of 188 (89) m and typically remains without site is approximately 150 km west of the eastern Finger extensive ice cover during the entire winter. Water tem- Lakes, these measurements provide vertical atmospheric perature measurements are collected 2 times per day in profiles that are the most representative of an air mass the northwestern portion of Seneca Lake (42851.439N, modified by Lake Ontario under typical northerly wind 76858.819W) at an approximate depth of 2 m (Fig. 3). conditions that occur during LE events in the Finger Lakes These measurements have provided a continuous record region. A total of 92 soundings occurred during events of upper-epilimnion (i.e., the top layer of water directly (16 for SYNOP, 45 for LOenh, and 31 for NYSFL). affected by air temperature and wind) water temperature The North American Regional Reanalysis (NARR; for three cold seasons (2006/07, 2007/08, and 2008/09). Mesinger et al. 2006) was used to examine large-scale In the absence of a longer record of Finger Lakes water composite atmospheric patterns using the National Oce- temperatures, the daily mean water temperature was anic and Atmospheric Administration Earth System Re- used in conjunction with the surface meteorological ob- search Laboratory (NOAA/ESRL) Physical Science servations from SYR, ROC, PEO, and ITH for Finger Division online utilities at the Climate Diagnostics Cen- Lakes LE events from 1995/96 through 2005/06 to esti- ter (http://www.cdc.noaa.gov). Composite analyses of mate environmental conditions. Seneca Lake mean daily SYNOP, LOenh, and NYSFL events were composed of water temperatures range from 188C in early October to 3-h NARR output parameters available between the near 38C in late January and early February (Fig. 4). For start and end times of identified events. The SYNOP, 1056 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

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 surface observations from 381, 638, and 211 time periods, respectively. Statistical comparative analyses were conducted 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 acriticalZ value of 1.96 (p # 0.05) to measure for significant differences. The results presented in this section provide information on the environmental conditions for SYNOP, NYSFL, and LOenh events, variations in environmental 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 extending southward across the eastern United States with temperatures of approximately 288C over the Finger Lakes 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 pressure were located farther westward for LOenh and SYNOP events, respectively. Surface and 850-hPa temperatures in the Finger Lakes region from the NARR composites were warmer for both LOenh and SYNOP events, with surface temperatures of approximately 248 and 268C, respectively. FIG. 5. NARR composite (a) 2-m surface temperature, (b) SLP 2) SURFACE CONDITIONS and 2-m wind, and (c) 850-hPa height and wind for NYSFL events. Isotherms, isobars, and isohypses are plotted using intervals of 38C, Notable temperature variations were found between 2 hPa, and 15 m, respectively. The black circle shows the location SYNOP, LOenh, and NYSFL event types using the of the eastern Finger Lakes region. The composite maps were surface station hourly observations (Fig. 6). The four- generated using the NOAA/ESRL Physical Sciences Division Web station group-mean temperatures for SYNOP, LOenh, site (http://www.cdc.noaa.gov/). MAY 2010 N O T E S A N D C O R R E S P O N D E N C E 1057

FIG. 6. Distributions of temperature (8C) at four surface sites FIG. 7. As in Fig. 6, but for temperature difference between (ITH, PEO, ROC, and SYR) for (a) SYNOP, (b) LOenh, and (c) average Seneca Lake water temperature and surface air tempera- NYSFL events. Asterisks represent extreme values, and open cir- ture (DT). cles represent outliers. and NYSFL are 26.68, 25.98,and210.58C, respectively. produced LE rainfall. In addition, approximately 50% of Statistical analysis established that temperatures for LE events with an event-average air temperature above SYNOP, LOenh, and NYSFL all differed significantly. 08C occurred during October. These results are similar to LSH09 showed that the different event types are well findings from a study by Miner and Fritsch (1997), which distributed across all months analyzed (i.e., each type used data from seven autumns (September–November for of event occurs in each month of October–March). 1988–94) to investigate LE precipitation in the vicinity of The statistical differences in temperatures were found Lake Erie. They found that LE precipitation (i.e., snow to be associated with conditions during differing event and rain) occurred during approximately 20% of days in type and not to be attributable to a systematic differ- September–November of each year, with the largest num- ence in seasonality of event type. Significant temper- ber of events in October, most of which produced LE rain. ature variations were not found across the different Hourly air temperatures measured at all stations were surface stations for most LE event types (Fig. 6). ROC used with Seneca Lake daily mean water temperatures temperatures were typically the warmest of all stations. to estimate the surface lake–air temperature difference For example, the ROC mean temperature during LOenh DT for each hour during events (Fig. 7). The mean DT events was 25.48C as compared with 26.08, 26.18,and for SYNOP, LOenh, and NYSFL events was 11.68, 11.68, 26.08C at SYR, PEO, and ITH, respectively. SYR tem- and 14.28C, respectively. Measurements of DT for NYSFL peraturesweresignificantlycolderthanattheothersta- were found to be statistically different than during tions during NYSFL events. The mean temperatures at SYNOP and LOenh events. Surface DT values for LE

SYR, ITH, PEO, and ROC for NYSFL events were events in the Finger Lakes region (DTmean 5 12.48C) 211.38, 210.48, 210.08,and210.08C, respectively. were smaller than those that Laird et al. (2009a) found

Surface temperatures were above freezing for 12.0% for Lake Champlain LE events (DTmean 5 16.78C). For of all observations during events, and 16.2% of events both regions, DT values were substantially larger than had an event-average air temperature above 08C (Fig. 6). those observed during LE events on the Great Salt This result is much different from temperature conditions Lake, which had mean and maximum DT values of 7.68 during Lake Champlain LE events, which very rarely and 14.28C, respectively (Steenburgh et al. 2000). (1 of 67 events identiﬁed during nine winters) had tem- Dewpoint temperatures were similar during SYNOP peratures above 08C (Laird et al. 2009a). This suggests and LOenh events, whereas NYSFL events had statis- that NYS Finger Lakes precipitation bands resulted in tically lower values. The mean dewpoint temperatures both LE snow and rain and that some events likely only for SYNOP, LOenh, and NYSFL events were 29.18, 1058 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

FIG. 8. As in Fig. 6, but for distributions of SLP (hPa) at three surface sites (PEO, ROC, and SYR). 21 FIG. 9. As in Fig. 6, but for wind speed (m s ).

29.18, and 213.48C, respectively. The dewpoint tem- Few calm wind observations were reported during LE peratures for LE events in the Finger Lakes region were events. Frequency analyses of hourly observations from significantly higher than those found to occur during all stations showed that 3.5% reported calm conditions Lake Champlain LE events (Laird et al. 2009a). Both the and 7.8% had measurements of wind speed of less than warmer temperatures and greater amount of atmospheric 2ms21. The wind speed conditions during Finger Lakes moisture measured during Finger Lakes LE events are LE events were considerably different than conditions undoubtedly a result of the upwind influence of Lake that occurred during Lake Champlain LE events, where Ontario and the significant modification to polar air hourly observations from stations within the Lake Cham- masses by the lake through positive (upward directed) plain Valley showed that 12.5% and 21.3% had calm sensible and latent heat fluxes. winds and wind speeds of less than 2 m s21, respectively. The average SLP increased across SYNOP (1014.9 hPa), 3) SOUNDINGS LOenh (1020.7 hPa), and NYSFL (1024.9 hPa) events (Fig. 8). The differences among all event types were Rothrock (1969) and Niziol (1987) found that during statistically significant. This finding is consistent with Great Lakes LE snowstorms a lapse rate of at least the the observed eastward shift of the SLP pattern from the dry adiabatic lapse rate from the surface to 850 hPa (i.e., NARR composites for SYNOP, LOenh, and NYSFL a difference in temperature between the lake surface events, where SYNOP events occur in the closest prox- and 850 hPa DT850 of $138C) was a necessary criterion imity to an area of low pressure. These variations in SLP for storm development. For Finger Lakes LE events, with LE event type were also associated with differences DT850 was determined using soundings from KBUF and in SLP distributions that had an impact on wind speeds. Seneca Lake mean water temperatures. Approximately

NYSFL events occurred under the weakest surface wind 88% of DT850 values obtained during Finger Lakes events conditions during any of the three types of LE events exceeded the condition of 138C. The average and vari-

(Fig. 9). The four-station group-mean wind speed during ability of DT850 values was largest (smallest) for NYSFL 21 NYSFL was 3.9 m s , whereas LOenh and SYNOP (SYNOP) events (Fig. 10a). The mean DT850 values for events had mean wind speeds of 4.5 and 4.9 m s21,re- SYNOP, LOenh, and NYSFL events were 18.68, 18.88,and spectively. Wind speeds during NYSFL were found to be 19.28C, respectively. These values are consistent with the statistically different than conditions that occurred during mean DT850 values found for Lake Champlain LE events, SYNOP and LOenh events. Wind directions were similar which ranged from 16.08 to 18.78C (Laird et al. 2009a). regardless of observing station or LE event type. In Approximately 93% of the 92 KBUF soundings col- general, wind directions were from the northwest, with lected during LE in the Finger Lakes region had a stable the median values ranging between 3108 and 3208. layer present in the lower troposphere. The base of MAY 2010 N O T E S A N D C O R R E S P O N D E N C E 1059

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 conditions 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 precipitation. When LE precipitation developed in association with the smaller Finger Lakes across the same type FIG. 10. Distribution of (a) temperature difference between lake and 850-hPa level and (b) height of the base of an existing stable of LE event, 1) temperatures were colder and DT values layer located in KBUF soundings for each lake-effect event type. were 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 a stable layer was defined as the height at which the were more frequently from the northwest when LE environmental lapse rate became less than the moist precipitation developed in association with the smaller adiabatic lapse rate. In most cases, the stable layer was Finger Lakes as compared with more northerly wind characterized as having a temperature inversion. The directions when LE precipitation developed only in as- stable layer was elevated above the surface, with a con- sociation with one or both of the larger Finger Lakes. vective mixed layer existing in all but six soundings (6.5%). Figure 10b shows that the mean height of the c. Comparison of transitional and solitary LE events stable-layer base during NYSFL events was significantly lower (1.2 km) when statistically compared with LOenh Both the surface SLP observations and NARR com- and SYNOP events (1.5 km). The lower stable-layer posite analyses suggest a sequential nature to the oc- base and presence of only Finger Lakes precipitation currence of the three LE event types identified for the bands during NYSFL events suggest that the precondi- Finger Lakes region (SYNOP, LOenh, and NYSFL). tioned boundary layer coming southward from Lake This result is similar to the finding of Ellis and Leathers Ontario was significantly reduced in depth and limited in (1996) that identified five synoptic patterns that were ability to support LE precipitation development down- associated with Great Lakes LE snowfall in western New wind of Lake Ontario without the supplementary con- York and northwestern Pennsylvania from Lakes Ontario tribution of latent and sensible fluxes from individual and Erie. Many of the identified events in the Finger Finger Lakes. Lakes region occurred as a solitary type; however, nearly Similar to surface wind speeds, 850-hPa wind speeds 14% occurred as transitional cases. The transitional cases were weakest for NYSFL events (mean 5 10.4 m s21) that occurred were SYNOP to LOenh (one event), and increased for LOenh (11.2 m s21) and SYNOP LOenh to NYSFL (nine events), and SYNOP to NYSFL (12.9 m s21) events. The 850-hPa wind directions con- (seven events). The sequential ordering of LE event type tained a larger northerly wind component than did the during these transitional cases provides support that surface observations. However, the vertical directional there is an evolutionary nature in the synoptic-scale shear from the surface to 850 hPa was typically small for pattern and boundary layer structure for different types NYSFL, LOenh, and SYNOP events, with median values of LE events. Only NYSFL solitary events and transi- of 288,168, and 208 km21, respectively. The small amount tional events containing an NYSFL time period were of directional shear is a necessary criterion suggested by examined since so few transitional events containing a Niziol et al. (1995) for favoring LE snowband develop- LOenh time period were identified. The differences ment in the Great Lakes region. between several environmental variables for these two 1060 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

TABLE 1. Mean environmental conditions for solitary and transitional NYSFL events. Variables include lake–air temperature difference DT and lake–850-hPa temperature difference DT850.

Solitary Transitional Variable NYSFL NYSFL Surface temperature (8C) 29.2 213.1 Dewpoint temperature (8C) 212.1 216.2 DT (8C) 13.4 16.1

DT850 (8C) 18.8 20.1 Surface 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

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 shallower 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 events is 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 the early 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 systems and climate variability, as well as for comparative analyses of necessary conditions for the development and FIG. 11. Monthly variability in (a) temperature difference DT and (b) event duration for each lake-effect event type. The hori- change in frequency of Finger Lakes events versus those zontal reference line in (b) shows the mean event duration (9.4 h) associated with lakes across a range of locations and sizes for Finger Lakes LE events. (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 a large water body located in close upwind proximity. The mesoscale circulations originating over Lake Ontario authors acknowledge that Lake Ontario is contributing to often contribute directly to the development of LE the development of NYSFL events; however, this linkage precipitation over the Finger Lakes. This leads to warmer is difficult to quantify without specialized measurements air temperatures, greater amounts of atmospheric mois- beyond the climatological and operational datasets cur- ture, and higher LE event frequency of Finger Lakes rently available. Cosgrove et al. (1996) used a simple LE events when compared with the colder and drier mesoscale model to complete several preliminary simu- climatological conditions and lower frequency of Lake lations of a Finger Lakes LE event (11 December 1993) Champlain LE events, which develop in a region without and suggested that Seneca and Cayuga Lakes were able MAY 2010 N O T E S A N D C O R R E S P O N D E N C E 1061 to support LE snow without the upstream presence of ATM 05-12233. We gratefully acknowledge support by Lake Ontario but that the smaller Finger Lakes were the Office of the Provost at Hobart and William Smith only able to support an enhancement to LE snow origi- Colleges. Any opinions, findings, conclusions, and rec- nating over Lake Ontario. The use of special atmospheric ommendations expressed in this publication are those of observations from strategically placed field facilities, such the authors and do not necessarily reflect the views of the as boundary layer profilers and atmospheric sounding National Science Foundation. systems, along with more comprehensive mesoscale model simulations, would be required to understand and quantify REFERENCES the influence of Lake Ontario boundary layer processes and mesoscale circulations on the development and fre- Agee, E. M., and S. R. Gilbert, 1989: An aircraft investigation of mesoscale convection over Lake Michigan during the 10 Jan- quency of Finger Lakes LE events. uary 1984 cold air outbreak. J. Atmos. Sci., 46, 1877–1897. This study provides a climatological analysis of the Braham, R. R., Jr., 1983: The Midwest snowstorm of 8-11 De- environmental and atmospheric conditions that occurred cember 1977. Mon. Wea. Rev., 111, 253–272. during 125 identified LE precipitation events in the New ——, 1990: Snow particle size spectra in lake effect snows. J. Appl. York State Finger Lakes region for 11 winters. The Meteor., 29, 200–208. ——, and M. J. Dungey, 1984: Quantitative estimates of the effect results complement findings from LSH09, that reported of Lake Michigan on snowfall. J. Climate Appl. Meteor., 23, on the frequency and temporal characteristics of Finger 940–949. Lakes LE events. An examination of climatological con- ——, D. A. R. Kristovich, and M. J. Dungey, 1992: Comparison of ditions during Finger Lakes LE events provides several lake-effect snow precipitation rates determined from radar unique findings. NYSFL events developed with the 1) and aircraft measurements. J. Appl. Meteor., 31, 237–246. Burnett, A. W., M. E. Kirby, H. T. Mullins, and W. P. Patterson, coldest temperatures, 2) largest lake–air temperature 2003: Increasing Great Lake–effect snowfall during the twenti- differences, 3) weakest wind speeds, 4) highest sea level eth century: A regional response to global warming? J. Climate, pressure, and 5) lowest height of the stable-layer base. 16, 3535–3542. Soundings collected during events showed that approxi- Burrows, W. R., 1991: Objective guidance for 0–24-hour and 24– 48-hour mesoscale forecasts of lake-effect snow using CART. mately 88% of DT850 values exceeded the established Wea. Forecasting, 6, 357–378. criteria of 138C and had a mean DT850 value of 18.98C. Cairns, M., J. Corey, and D. Koracin, 2001: A numerical simulation In addition, the base of a stable layer during NYSFL of a rare lake-effect snowfall in Western Nevada. Proc. 14th events was found exclusively below 2.1 km and the Conf. on Numerical Weather Prediction, Ft. Lauderdale, FL, mean height was substantially lower than for LOenh Amer. Meteor. Soc., JP1.14. [Available online at http://ams. and SYNOP events. confex.com/ams/WAF-NWP-MESO/techprogram/paper_22959. htm.] Several significant differences in conditions were Callinan, C. W., 2001: Water Quality Study of the Finger Lakes. found when only one or both of Cayuga and Seneca New York State Department of Environmental Conservation Lakes, the largest Finger Lakes, had LE precipitation Rep., 152 pp. [Available online at http://www.dec.ny.gov/ as compared with when the smaller Finger Lakes also lands/25576.html.] produced LE precipitation. Last, transitional events con- Carpenter, D. M., 1993: The lake effect of the Great Salt Lake: Overview and forecast problems. Wea. Forecasting, 8, 181–193. taining an NYSFL time period occurred in association Cosgrove, B., S. Colucci, R. Ballentine, and J. Waldstreicher, 1996: with significantly colder and drier air masses, larger lake– Lake effect snow in the Finger Lakes region. Proc. 15th Conf. air temperature differences, and a less stable and shal- on Weather Analysis and Forecasting, Norfolk, VA, Amer. lower boundary layer when compared with those of Meteor. Soc., 573–576. solitary NYSFL events. Ellis, A. W., and D. J. Leathers, 1996: A synoptic climatological approach to the analysis of lake-effect snowfall: Potential forecasting applications. Wea. Forecasting, 11, 216–229. Acknowledgments. The second and third authors con- ——, and J. J. Johnson, 2004: Hydroclimatic analysis of snowfall ducted this research during the 2005 and 2006 summer trends associated with the North American Great Lakes. undergraduate research program at Hobart and William J. Hydrometeor., 5, 471–486. Smith Colleges. Helpful comments from Michael Evans Hjelmfelt, M. R., 1990: Numerical study of the influence of environmental conditions on lake-effect snowstorms on Lake and Michael Jurewicz of the Binghamton, New York, Michigan. Mon. Wea. Rev., 118, 138–150. National Weather Service Forecast Office and David Kristovich, D. A. R., and R. R. Braham Jr., 1998: Mean profiles of Kristovich of the Illinois State Water Survey greatly moisture fluxes in snow-filled boundary layers. Bound.-Layer aided this investigation. We appreciate assistance from Meteor., 87, 195–215. the Northeast Regional Climate Center and National Lackmann, G. M., 2001: Analysis of a surprise western New York snowstorm. Wea. Forecasting, 16, 99–116. Climatic Data Center in obtaining the data necessary for Laird, N. F., D. A. R. Kristovich, and J. E. Walsh, 2003a: Idealized this project. This research was supported by the National model simulations examining the mesoscale structure of win- Science Foundation under Grants ATM 02-02305 and ter lake-effect circulations. Mon. Wea. Rev., 131, 206–221. 1062 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49

——, J. E. Walsh, and D. A. R. Kristovich, 2003b: Model simula- Payer, M., J. Desrochers, and N. F. Laird, 2007: A lake-effect snow tions examining the relationship of lake-effect morphology to band over Lake Champlain. Mon. Wea. Rev., 135, 3895–3900. lake shape, wind direction, and wind speed. Mon. Wea. Rev., Portis, D. H., M. P. Cellitti, W. L. Chapman, and J. E. Walsh, 2006: 131, 2102–2111. Low-frequency variability and evolution of North American ——, J. Desrochers, and M. Payer, 2009a: Climatology of lake-effect cold air outbreaks. Mon. Wea. Rev., 134, 579–597. precipitation events over Lake Champlain. J. Appl. Meteor. Rothrock, H. J., 1969: An aid in forecasting signiﬁcant lake snows. Climatol., 48, 232–250. Tech. Memo. WBTM CR-30, National Weather Service, ——, R. Sobash, and N. Hodas, 2009b: The frequency and char- Central Region, 16 pp. acteristics of lake-effect precipitation events associated with Schmidlin, T. W., and J. Kosarik, 1999: A record Ohio snowfall the New York State Finger Lakes. J. Appl. Meteor. Climatol., during 9–14 November 1996. Bull. Amer. Meteor. Soc., 80, 48, 873–886. 1107–1116. Lavoie, R. L., 1972: A mesoscale numerical model of lake-effect Schroeder, J. J., D. A. R. Kristovich, and M. R. Hjelmfelt, 2006: storms. J. Atmos. Sci., 29, 1025–1040. Boundary layer and microphysical inﬂuences of natural cloud Mesinger, F., and Coauthors, 2006: North American Regional seeding on a lake-effect snowstorm. Mon. Wea. Rev., 134, Reanalysis. Bull. Amer. Meteor. Soc., 87, 343–360. 1842–1858. Miner, T. J., and J. M. Fritsch, 1997: Lake-effect rain events. Mon. Schultz, D., D. Arndt, D. Stensrud, and J. Hanna, 2004: Snowbands Wea. Rev., 125, 3231–3248. during the cold-air outbreak of 23 January 2003. Mon. Wea. Niziol, T. A., 1987: Operational forecasting of lake effect snow- Rev., 132, 827–842. fall in western and central New York. Wea. Forecasting, 2, Scott, R. W., and F. A. Huff, 1996: Impacts of the Great Lakes on 310–321. regional climate conditions. J. Great Lakes Res., 22, 845–863. ——, W. R. Snyder, and J. S. Waldstreicher, 1995: Winter weather Steenburgh, W., and D. J. Onton, 2001: Multiscale analysis of the forecasting throughout the eastern United States. Part IV: 7 December 1998 Great Salt Lake–effect snowstorm. Mon. Lake effect snow. Wea. Forecasting, 10, 61–77. Wea. Rev., 129, 1296–1317. Norton, D. C., and S. J. Bolsenga, 1993: Spatiotemporal trends in ——, S. Halvorson, and D. Onton, 2000: Climatology of lake-effect lake effect and continental snowfall in the Laurentian Great snowstorms of the Great Salt Lake. Mon. Wea. Rev., 128, Lakes, 1951–1980. J. Climate, 6, 1943–1956. 709–727. Onton, D. J., and W. J. Steenburgh, 2001: Diagnostic and sensitivity Walsh, J. E., A. S. Phillips, D. H. Portis, and W. L. Chapman, 2001: studies of the 7 December 1998 Great Salt Lake–effect Extreme cold outbreaks in the United States and Europe, snowstorm. Mon. Wea. Rev., 129, 1318–1338. 1948–99. J. Climate, 14, 2642–2658.