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NOAA/NWS National Weather Service
Binghamton, New York
A dataset of central New York and northeast Pennsylvania severe weather and flash flood events occurring in environments characterized by small mixed-layer convective available potential energy (MLCAPE) and large 0-6 km bulk shear was examined for the period from 2003 to 2009. A local study of these events is presented, and results from research to discriminate between high-impact and low-impact severe events are shown.
Results from the study indicate that low MLCAPE / high 0-6 km shear (LCHS) events were most often associated with a small number of severe weather and/or flash flood reports. However a subset of more significant LCHS events was identified. These LCHS events most often occurred during the afternoon or evening, and were most often associated with damaging winds. The majority of events occurred during the cool season, though several warm-season events were also identified. High-impact, cool-season events were mostly associated with lines of convection, while the majority of warm-season high-impact events were associated with isolated cells. LCHS events associated with flash flooding tended to be associated with smaller low-level lapse rates, smaller dewpoint depressions and smaller 500-hPa height falls than events that were associated with severe weather, but no flash flooding.
High-impact, warm-season severe events typically occurred in environments characterized by steep low-level lapse rates, deep layers of dry air, and a strong, west-northwest flow aloft. By contrast, most of those characteristics were not found to correlate significantly with number of severe reports during the cool season. Cool-season parameters that exhibited the highest correlation with the number of severe reports were mainly related to wind speed and 12-h 500- hPa geopotential height falls, indicating that the strength and speed of eastward progression of the synoptic-scale forcing is critical for producing major LCHS events during the cool season.