A climatology of the spatial and temporal distribution of convection over the Northeast United States

The goal of this presentation is to highlight the spatial distribution and evolution of deep convection over the Northeast U.S. during the warm season (April through September). There is little knowledge of where convection is initiated over the Northeast U.S. in relation to the terrain, coastal, and urban areas. It is also not well known how convection evolves diurnally and as the warm season progresses. A convective climatology was constructed for the Northeast U.S. using 2km by 2km resolution NOWrad radar data from 1996-2007 as well cloud-to-ground lightning from the National Lightning Data Network (NLDN) from 2002-2007. The lightning counts were interpolated to a 10km by 10km grid over the Northeast U.S.

The frequency of convection at each grid point over the Northeast U.S. was obtained by summing every 15-min the composite reflectivity values that are at least 45 dbZ. There are preferred regions for convection within the Hudson Valley, western and southeast Pennsylvania, central New Jersey and into the Delmarva Peninsula. A favored initiation area includes the immediate lee of the Appalachians. There is a sharp gradient in convective frequency immediately west of the coast (around New York City) as a result of the cooler marine boundary layer. As the warm season progresses, the convective activity shifts more towards the coast, which is consistent with the warming sea surface temperatures. During the mid-day period (18-00 UTC), the maximum convection is clearly over inland areas, but by late at night (06-12 UTC) the convective maximum shifts more offshore of the southern New England coast. Composites using the North American Regional Reanalysis (NARR) to highlight some of the flow patterns attached to the favored areas of convective development. The various life cycles of convection over the Northeast are analyzed using Hovmoller plots to highlight genesis and decay regions.