Wednesday, 29 October 2008: 2:30 PM
South Ballroom (Hilton DeSoto)
Lake-effect snowstorms which form parallel to the long axis of a Great Lake can produce enormous snowfall rates and total storm accumulations (> 5 cm hr-1
and > 130 cm, respectively). These storms have also been observed to become electrified with significant lightning production. Long lake axis-parallel (LLAP) bands have different structure and dynamics from the wind-parallel rolls mainly associated with the western Great Lakes. They form as a single band over the lake and model results show a thermally direct transverse circulation sets up along the entire band, with latent and sensible heating with thickness increases being the main forcing. Linear CISK (Conditional Instability of the Second Kind) is hypothesized to allow these bands to become very intense (radar reflectivity values approach 40 dBZ) and last long after synoptic conditions become unfavorable for lake-effect storms (e.g., the LLAP band continues to produce significant snowfall several hours after low-level warm air advection develops across the region). As a band moves onshore at the eastern end of Lake Ontario, the upward vertical motion within the band is enhanced by topographical influences. The cold wedge, which develops along the western flank of the Tug Hill Plateau, acts like an extension of the hill and produces a broad area of stronger uplift and enhanced snowfall. The forecasting of the band location and intensity can be quite challenging as upwind lake bands/moisture plumes (from Lake Huron) can connect with the bands over Lakes Erie and Ontario. These lake-to-lake band connections typically intensify the downwind counterpart, but the effect on band location is not well-understood. Many of these phenomena have only been modeled but not observed. SUNY Oswego meteorologists plan to conduct additional field research to observe these conditions and test hypotheses for their development.
Lake-effect thunderstorms are typically observed early in the lake-effect season across the eastern Great Lakes (September-December). They are associated with the LLAP type bands and anecdotal evidence suggests a significant fraction of the lightning is intracloud. Total flash rates were 1 flash (2 min)-1 in one storm. A field project is being planned for the eastern Great Lakes that will include total lightning observations (cloud-to-ground and intracloud from the National Lightning Detection Network), mobile Doppler radars, rawinsonde, and electric field observations to study this phenomenon that is not well-understood.
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