Convective initiation and evolution approaching the southern New England coast and Long Island

Although severe convection is not as frequent across the Northeastern U.S. as the central U.S., it still occurs and endangers tens of millions of people. While there is some evidence that interior Northeast U.S. terrain can significantly influence convection, much less is known about convective evolution near the southern New England coast and Long Island, where millions of people live. In this coastal region, the coastal marine layer, sea breeze circulations, and possibly the urban centers can modify convection. In order to obtain some preliminary understanding of the distribution of convection around southern New England and Long Island, cloud-to-ground (CG) lightning and WSR-88D data from Upton, NY (OKX on Fig. 1a) were utilized on a 2-km grid for all severe thunderstorm events in the region for the past 6 years. This illustrates a sharp decrease of lightning frequency and composite reflectivity intensity across Long Island, which suggests that relatively cool marine layer often weakens deep convection rapidly in this region. Interestingly, the greatest some of the greatest frequencies of strong reflectivity (> 50 dBZ) are located near New York City (NYC) and extreme southwest Connecticut, which suggests that a fraction of storms intensify as they interact with the more urban areas or possible sea breeze boundaries.

This poster will also highlight the rapid evolution of the 1 June 2006 convective event over southern New England. On the afternoon of 1 June 2006, convection initiated near the lee trough over northwest New Jersey and it became organized into a line moving eastward towards NYC by 2200 UTC, while the lee trough remained to the west. A WRF simulation was initialized at 0000 UTC 1 June using the NOGAPS analyses and WSM3 microphysics (best member that day in Stony Brook WRF ensemble) nested down to 1.33-km grid spacing. The 1.33-km WRF is shown to realistically simulate the convective development, and the subsequent weakening rapidly over Long Island as compared to WSR-88D, ACARS data, and the surface mesonet. A separate WRF simulation without the Appalachian terrain will highlight the importance of the lee trough in the convective initiation, while another simulation with the coast shifted to the east will quantify the impact of the relative cool sea surface temperatures in the control run.