Warm, humid air swelling over the Washington region will help fuel widespread showers and thunderstorms through tonight that could cause flooding. There’s also a possibility that a few storms may be severe, unleashing damaging wind gusts and hail.

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       Multiple waves of downpours are possible. The first is expected between 6 and 10 p.m., with at least one or two more rounds possible through the predawn hours. Severe storms most likely come during the first wave of storms.

       Rainfall totals may average just 0.5 to 1 inch, but amounts could reach 2 to 3 inches in a few areas, falling over a short duration.

       “Areas that receive multiple storms in quick succession could experience flooding or flash flooding as a result,” the National Weather Service wrote in a discussion.

       A flood watch is in effect until 3 a.m. everywhere except Southern Maryland.

       The Flood Watch this evening has been expanded (areas in green), for the potential of flash flooding, with the possibility of gusty winds. Stay weather aware and see https://t.co/Kt74D8dUsR for the latest. #DCwx #MDwx #VAwx #WVwx pic.twitter.com/VpSzy4TqI4

       — NWS Baltimore-Washington (@NWS_BaltWash) June 8, 2022

       Rainfall rates could reach 2 inches per hour, increasing the possibility of overflowing streams and flooding in areas with poor drainage.

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       It’s much harder at night for drivers to spot areas of ponding and flowing water, so extra vigilance is needed. Please heed the important advice to “turn around, don’t drown” if you encounter a flooded road.

       Discussion

       At play through tonight is an approaching low-pressure system with a stalled frontal boundary over the region. Along and south of this front, a moderately unstable and very humid air mass is developing. These elements are shown in the surface forecast map for 8 p.m.:

       At higher altitudes, an intensifying disturbance embedded in the jet stream is approaching from the Ohio Valley, shown below. It will increase uplift of air over our region, particularly during the evening and overnight hours.

       Meanwhile, atmospheric moisture levels will be very high for this time of year. Precipitable water, a measure of this moisture, may exceed 2 inches — or twice the norm (closer to 1 inch). Those 2-inch pockets are highlighted in red in the forecast map below.

       The combination of an increasingly unstable atmosphere, dynamic uplift and a nearby frontal boundary — along with brisk winds in the middle atmosphere — raise the possibility of isolated severe thunderstorms into the evening.

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       The Weather Service’s Storm Prediction Center has declared a Level 1 out of 5 risk for severe storms. The main threats will be intense lightning and isolated instances of small hail and damaging wind gusts.

       Over 90 million people face severe storm risk in Lower 48 on Wednesday

       The greater, more widespread hazardous weather threat will be flash flooding. The combination of very high precipitable water, jet stream dynamics, a stalled front, and an unstable air mass coinciding during darkness — along with recent rains that have dampened the ground — is a potent flash flood setup. The Weather Prediction Center has placed the area in a Level 2 out of 4 risk for excessive rainfall.