Special focus: Another Mid-Atlantic heavy rainfall event

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An approaching slow-moving cold front causes another excessive rainfall event later today and this evening in the Mid-Atlantic region aggravating already flood-ridden areas in Maryland and Pennsylvania.

Severe weather/flooding rainfall Mid-Atlantic today

Discussion: A slow-moving cold front moves into the East U.S. today igniting severe thunderstorms and another heavy rainfall event. A low pressure area forms on the front just west of Washington, DC early this evening enhancing an early-to-middle evening heavy rain across areas which are already in flood conditions. The front moves slowly to the East Coast by tomorrow morning.

Yesterday, severe weather reports featuring mainly damaging wind gusts were reported in the northeast Ohio Valley (Fig. 1). This type of wind damage shifts to the Mid-Atlantic region today where a severe weather risk area is forecast by NOAA/SPC (Fig. 2).

Excessive rainfall is forecast by NOAA/WPC in the Mid-Atlantic region (Fig. 3). Rainfall amounts could reach several in. across this zone which is already flooded by recent historic rainfall. The concern is the extremely unstable atmosphere (>3000 j/kg CAPE values) coupled with super high humidity due to excessive ground moisture could cause rainfall amounts to easily exceed 3 in.

The HRRR model indicates peak intensity of rainfall is early to middle evening in the Washington to Baltimore to Philadelphia stretch (Fig. 4). Dangerous life-threatening flash flooding could occur in this area at that time.

Figure 1: Yesterday’s damaging wind gust zone shifts east to the Mid-Atlantic today.

Figure 2: Today’s severe weather outlook zone for the Mid-Atlantic region.

Figure 3: Today’s excessive rainfall forecast which could over achieve in DC, MD and PA.

Figure 4: HRRR model indicates strongest intensity of rainfall is 8-9 PM from Washington to Philadelphia.