Messages
Scattered showers and thunderstorms will continue into the early overnight period tonight.
A Flood Watch has been issued for Tuesday into Wednesday as an impactful system arrives across the region.
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Revised in 4 passages since the 2:55 PM discussion. See every revision.
Discussion
KEY MESSAGE 1. Scattered showers and thunderstorms will continue into the early overnight period tonight.
Scattered showers and thunderstorms have developed across the northern Middle Atlantic region this afternoon as increasing heat and moisture have arrived along with a few upper short waves. We are not expecting widespread severe weather, but with the possibility of strong downpours and some damaging winds could occur in a few spots, the Marginal risk for severe storms remains across our area for that reason.
The storms will be slow moving, so localized flooding is possible through the tonight period as well. A slight risk for excessive rainfall remains for Delaware tonight. The activity is expected to decrease after sunset.
KEY MESSAGE 2. A Flood Watch has been issued for Tuesday into Wednesday as an impactful system arrives across the region.
As the upper heights continue to drop and summertime warmth and humidity continue. Tuesday looks to feature the more widespread showers and thunderstorms. The H5 height falls and jet dynamics aloft will favor convective development nearly all day as surface low pressure develops just to our west. This will keep a steady stream of warm, moist air pumping into the area and keeping the environment conditionally unstable despite cloud cover. PWats will rise to near 2" by the end of the day. Some models suggest we could have a stalled or slow moving frontal boundary across the central or northern portion of the forecast area, which could act as a focusing mechanism for heavy rainfall. Heavy rain leading to flash flooding could end up being a bigger concern and greater impact than the severe thunderstorm threat.
The latest outlooks from WPC show most of our area in a SLIGHT risk for excessive rainfall, but northern NJ has a MODERATE risk for excessive. A flash flood watch has been issued for Tuesday and into Wednesday. As for severe weather, the southern half of the area including Delmarva, south NJ and metro Philadelphia have a SLIGHT risk for severe thunderstorms while areas to the north are in a MARGINAL risk. Damaging winds are the primary threat with thunderstorms on Tuesday.
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