Cool-Season Severe Weather in the Northeast U.S

Forecasting severe weather events during the cool season can be challenging in the Northeast U.S. because of the rarity of these events. For example, Albany, NY, averages about one thunderstorm day every decade in the month of February. Despite the rarity of cool-season severe weather in the Northeast, when it does occur it can cause considerable property damage. During the cool season (defined here as 15 October through 15 April), severe weather typically occurs in advance of a cold front associated with a midlatitude cyclone. The environment conducive to cool-season severe weather in the Northeast is typically characterized by strong mid and upper-level jets, marginal convective available potential energy (CAPE), large deep-layer (0–6 km) shear, large horizontal gradients of equivalent potential temperature, and high values of precipitable water.

The purpose of this presentation is to determine the frequency and location of cool-season severe weather events in the Northeast, and to document the meteorological parameters that typify the synoptic-scale environment for these events. Storm reports from the Storm Prediction Center (SPC) are used to examine the spatial and temporal frequency of tornadoes, hail, and high wind events. The SPC dataset will be used to prepare a climatology that documents the spatial and temporal frequency of cool-season severe weather events in the Northeast. The results of the climatology will be used to develop composite analyses from the NCEP–NCAR reanalysis dataset of mean sea level pressure, CAPE, mixed-layer CAPE, 0–6 km shear, precipitable water, mid- and upper-level wind speed, and ascent at several times encompassing the life cycle of the composite severe weather event. The composite analysis is expected to reveal various features that have been hypothesized to characterize Northeast cool-season severe weather events, including enhanced forcing for ascent associated with an intense upper-level jet streak and a strong mid-level wind speed maximum.