A climatology of convective system morphology over the Northeast United States

The organizational modes of convection are often related to the type of severe weather most likely to occur (tornadoes, straight-line winds, and/or flash flooding). Previous work has classified the convective modes over the Central U.S., but a similar study for the Northeast U.S. does not exist. The ambient environment over the Northeast is much different than the Plains, typically with less CAPE over the Northeast as well as influences by the Appalachian terrain, coastal marine boundary layer, and major urban metropolitan areas, such as New York City.

The different modes of convection over the Northeast were identified during the 2004-2007 warm seasons. In order to compare the results with the Central U.S., the same approach was used as in Gallus et al. (2008). This involved perusing hourly NOWRAD (2-km grid-spacing) radar imagery and classifying the convection into four types of cellular convection (individual cells, clusters of long-lived cells, clusters of short-lived pulse cells, and broken squall lines), five types of linear systems (bow echoes, squall lines with trailing stratiform rain, lines with leading stratiform rain, lines with parallel stratiform rain, and lines with no stratiform rain), and nonlinear systems. Preliminary results suggest that the cellular mode dominates over linear systems in the Northeast, and there are some preferred genesis zones of linear and cellular convection in the lee of the Appalachians. This presentation will highlight the various convective modes in relation to the severe weather reports, diurnal time periods, average lifetime, and the large-scale environmental conditions. These results will also be compared with the Central U.S.

References:

Gallus, W.A., N.A. Snook, and E.V. Johnson, 2008: Spring and Summer Severe Weather Reports over the Midwest as a Function of Convective Mode: A Preliminary Study. Wea. Forecasting, 23, 101–113.