8:00 p.m. update: The severe thunderstorm watch issued earlier has been canceled. Storms have weakened and just widely scattered shower lingers over the area.

This is the last update of the evening. Scroll down for the forecast for the rest of tonight and Wednesday. (See the bottom of this post for updates which have expired)

Original post

A solid convective line developing over the mountains is approaching the Washington-Baltimore region. There is a severe thunderstorm watch in effect, and we will run the risk of a severe storm this afternoon and evening, which could produce large hail or even a tornado. The timing — around evening rush hour — could be a problem for commuters.

Expect showers and thunderstorms to arrive between 5 p.m. and 8 p.m. from northwest to southeast, with brief heavy downpours, intense lightning and strong wind gusts. There could be some isolated areas that experience damaging wind gusts and large hail.

Through tonight: Storms moving into the area this afternoon should continue into well into the evening. It’s possible the worst of the activity will focus north and west of the city, where a severe thunderstorm watch is now in effect. A break is possible late night, but more rain probably develops by sunrise. Lows range from the low to mid-60s in the cooler suburbs to closer to 70 downtown.

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Tomorrow (Wednesday): A strong cold front is moving through, but slowly. Upper-level winds will align with it to keep moisture streaming over the area through Wednesday. A surface low might form in the region as well. All recipes for at least occasional rain, sometimes moderate to heavy. And it could be an all-day rain if we really luck out. High temperatures end up somewhere near 70, although if it rains much of the day, 60s seem a bit more likely.


The Capitol in late August. (Kevin Wolf via Flickr )

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Pollen update: Pollen is active lately! Mold spores and weed pollen are moderate/high. Tree pollen is moderate. Grass pollen is low/moderate.

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Expired updates

5:30 p.m. update: A new severe thunderstorm warning has been issued from roughly Front Royal to Leesburg through 6 p.m. Spotty damaging wind gusts and some hail is possible with this cluster of storms.

The closest storm activity to Washington stretches from northern Fairfax County through central Montgomery County is pushing east. It should clip areas on the north side of the Beltway over the next hour.

Showers and storms to the southwest should move into rest of the metro region between 6 and 8 p.m. from southwest to northeast with some downpours and thunder/lightning possible.

4:45 p.m. update: Thunderstorms northwest of Washington from roughly Brunswick to Westminster have weakened some, but some intense storms extend to the southwest from roughly Lovettsville to Front Royal, where a severe thunderstorm warning was issued through 5:30 p.m. Heavy downpours, lightning, and some isolated damaging wind gusts are the main hazards of concern with these storms.

4:10 p.m. update: Severe thunderstorm warnings are being issued for this line of thunderstorms in our far northwest areas as it rolls east. The main threats appear to be strong wind gusts up to 60 or 70 mph and quarter-size hail. Of course, the heavy downpours alone will be enough to disrupt the evening commute.

Jeff Halverson contributed to this post.