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D.C.-area forecast: Heat index near 100 this afternoon with threat of heavy downpours late today

A flood watch is in effect this afternoon and tonight

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Radar courtesy MyRadar | © OpenStreetMap contributors

* Flood watch from 3 p.m. through late tonight *

10 a.m. — Numerous storms, patchy flooding possible this afternoon and evening

Thunderstorms riding overtop the heat dome over the middle over the country (and from the remnants of a derecho in the Plains and Midwest) are likely to move into the region later this afternoon and into the evening. It’s not yet clear whether they’ll be widely scattered or widespread but, as it’s very warm and humid, any storms will have the potential to produce very heavy rain.

As such, the National Weather Service has issued a flood watch for the region this afternoon and tonight.

“Multiple rounds of scattered to numerous showers and thunderstorms are likely this afternoon and tonight,” the Weather Service writes. “The most likely time period for thunderstorms producing heavy rain and potential flash flooding is this evening, but thunderstorms could develop as early as this afternoon, and may linger well into the night. Several inches of rain is possible in a short period of time, which would cause rapid rises of water.”

In addition to heavy rain and lightning, a few storms could be severe and producing some damaging wind gusts as well. Stay tuned for additional updates as storms develop later today.

Original forecast from 5 a.m.

Today’s daily digit

A somewhat subjective rating of the day’s weather, on a scale of 0 to 10.

4/10: Gross humidity, a heat index peaking near 100, and an ever-present chance of a storm (yet much of the day should be dry).

Express forecast

  • Today: Partly sunny, humid, a few showers and storms possible. Highs: Low 90s.
  • Tonight: Mostly cloudy and muggy, chance of scattered showers/storms. Lows: 70s.
  • Tomorrow: Mostly cloudy, scattered showers/storms possible. Highs: Mid- to upper 80s.

Forecast in detail

Got to admit, we’re in the midst of a pretty frustrating forecast period. The main issue being that when we’ve got this much moisture in the air and a stalled front nearby, we can say there’s a chance of showers and storms every day, but it’s hard to pinpoint when and where storms will develop and how numerous they’ll be. What we do know is that it’s a good idea to have the umbrella handy.

Today (Wednesday): Partly sunny and humid again. We’re headed for afternoon highs in the low 90s. And with the very high humidity (dew points in the low to mid-70s), the heat index should top out near 100. With this much moisture in the air and a frontal boundary nearby, an isolated shower or storm could develop at just about any time. Confidence: Medium

Tonight: We have a better chance of more numerous showers and storms this evening and overnight. Some storms could produce flooding given the recent rainfall. Lows only fall back to the muggy low to mid-70s under mostly cloudy skies. Confidence: Medium

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Tomorrow (Thursday): Mostly cloudy skies should hold temperatures back a bit, with highs topping out in the mid- to upper 80s. But the humidity remains very high with a chance of scattered showers and storms throughout the day. Confidence: Medium

Tomorrow night: Scattered showers and storms remain possible through the night. No let up in the mugginess with mostly cloudy skies and lows in the low to mid-70s again. Confidence: Low-Medium

A look ahead

More of the same with a chance of scattered showers and storms Friday and Friday night. Still humid on Friday with partly to mostly cloudy skies and highs in the mid-80s to near 90. Friday night lows dip to near 70. Confidence: Low-Medium

The weekend starts on an uncertain note. High pressure tries to build in from the northwest on Saturday, but it’s not clear whether it will build in strong enough or fast enough to clear out the clouds and eliminate the chance of showers and storms. Sunday has a better chance to be rain-free with brighter skies and lower humidity. Highs both days should be in the low to mid-80s. Confidence: Low-Medium