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* Flash Flood Watch from this afternoon and evening *

12:55 p.m. — Rain could be extremely heavy through this evening, up to 1 to 2 inches in 15 to 30 minutes

The National Weather Service has increased the risk of excessive rainfall in the Washington region from slight to moderate as ingredients seem to be coming together for localized very heavy downpours. In a special bulletin, the Weather Service mentions the potential for “1-2 inches of rain in 15 to 30 minutes.”

Heavy storms have already developed north of the Beltway, particularly just east of Ellicott City to around Baltimore. We expect storm activity to flare up closer to the D.C. metro area by late afternoon.

“While flash flooding is not expected to be widespread across the entire region, scattered to numerous slow moving thunderstorms will produce heavy rainfall with several areas at risk for flash flooding,” the Weather Service wrote.

11:40 a.m. — Flash flood watch goes into effect starting at noon

A flash flood watch takes effect at noon and continues through midnight. Short-term models indicate showers and storms will become numerous by late this afternoon and, in some areas, produce a lot of rain in just an hour or two.

“Because of the slow motion and ample moisture in the atmosphere, storms may drop 2 to 4 inches of rain in a short period of time, resulting in flash flooding," the National Weather Service cautions.

While the heaviest rain may occur in the late afternoon and early evening, scattered downpours could linger even past sunset and through the overnight hours.

Modeling suggests the threat of flooding rain will tend to be isolated to widely scattered rather than widespread. In other words, a few areas may experience very heavy downpours that cause flooding while others are passed over. We’ll post updates as needed as showers and storms flare up.

Today’s daily digit

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

5/10: Temperatures are warm but conform to the norm; showers may wait until late, which would be great.

Express forecast

  • Today: Variably cloudy; showers and maybe a storm, especially in the afternoon. Highs: 82 to 86.
  • Tonight: Frequent showers with an isolated thundershower possible. Lows: 60 to 64.
  • Tomorrow: Cloudy, scattered showers throughout the day. Highs: 67 to 71.

Forecast in detail

A lumbering zone of low pressure pinwheels across the area over the next two days, producing intermittent showers while keeping us guessing as to when outdoor activities are safe. Friday will be shockingly cooler (think a high near 70), but the weekend is seasonably warm and mainly dry.

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Today (Thursday): There will be plenty of clouds but probably enough breaks of sun to push highs into the low to mid-80s. Humidity levels are high (dew points near 70), making it less than comfortable. A shower could pop up almost any time, but most should wait until mid- to late afternoon to fire up. A thundershower is possible but not likely to be severe. Winds are minimal. Confidence: Medium-High

Tonight: Showers become more numerous through the night and a stray thundershower is still possible. Easterly breezes are very light. Lows mainly hold in the low 60s. Confidence: Medium-High

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Tomorrow (Friday): Showers remain active through the day with little if any sun time. Temperatures barely climb, and highs in the upper 60s to low 70s give air-conditioning units a needed break. Light breezes come from the east. Confidence: Medium

Tomorrow night: There is little letup in the scattered showers until very late night. Much of the area could end up with an inch of rain or better from this two-day event. Lows slip to the upper 50s to low 60s. Confidence: Medium

A look ahead

Skies should partially clear on Saturday and, with a little luck, showers should be out of the picture. Highs hold in the upper 70s to low 80s. The first sign of the new crescent moon shows up early evening, hovering over Venus in the west, and will be over Mars the next night. Overnight lows are mainly in the low to mid-60s. Confidence: Medium

Sunday is partly sunny and high temperatures scoot back up to mainly the mid-80s. Fortunately, humidity levels are still moderate. Showers and a stray thundershower are a decent bet later in the day and into the evening. Overnight lows fall to the low to mid-60s. Confidence: Medium

Mainly sunny skies on Monday allow highs to still reach the mid- to upper 80s even though cooler air is starting to move in. Confidence: Medium