1052 JOURNAL OF APPLIED METEOROLOGY AND CLIMATOLOGY VOLUME 49 Climatological Conditions of Lake-Effect Precipitation Events Associated with 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 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 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 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 atmo- spheric 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 pro- vide 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 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 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.