Identifying Key Features to Predict Significant Severe Weather Outbreaks in the Northeast United States

On 1 June 2011, a significant severe weather event occurred in the northeastern U.S. with multiple reports of hail greater than 3 inches in diameter in New York and New England and an EF3 tornado in Massachusetts. This significant severe weather event had similar atmospheric characteristics to other historical significant severe weather events, defined by the Storm Prediction Center as hail greater than 2 inches in diameter, straight-line winds of ≥65Kt and/or tornadoes of EF2 magnitude or greater. A previous study compared significant severe weather events with severe weather forecast busts (no tornadoes reported within the majority of a tornado watch or within a moderate risk region) in the Carolinas through the mid-Atlantic states, and identified atmospheric features that contributed to the occurrence of significant severe weather outbreaks in that region. That study researched 14 significant severe weather events from 1984 to 2002, and identified atmospheric characteristics that contributed to the development of the significant severe weather outbreak.

In this study, 20 significant severe weather events in the northeastern U.S. from 1953 to 2011 that produced F2/EF2 tornadoes were researched to determine if the atmospheric features in the Carolinas and mid-Atlantic events had similarities to the northeastern U.S. events. It was determined after researching these northeastern U.S. events, as well as selected forecast busts between 2003 and 2010, that the key atmospheric features supportive of significant severe weather in the Carolinas and mid-Atlantic were also valid for the northeastern U.S. Atmospheric features that will be presented include 850 hPa winds, equivalent potential temperatures, 4-layer best lifted index and 850 hPa and 500 hPa heights and temperatures. It was determined that a progressive 850 hPa and 500 hPa vorticity center and 850 hPa equivalent potential temperature change of ≥25K in 12 hours over the region identified the strong low-level forcing that supported significant severe weather events. Other important features were surface based instability and an 850 hPa wind maximum ≥40Kt.

Future studies will include analyzing elevated mixed layers, values of Convective Available Potential Energy and deep layer shear.