NEW: Flood Watch issued for Arlington and D.C. area

Flood Watch boundaries and radar (via National Weather Service)
Arlington and much of the D.C. area is now under a Flood Watch.
Slow-moving storms might dump lots of rain in short order this afternoon and evening, causing flooding, forecasters say.
More from the National Weather Service:
…FLOOD WATCH IN EFFECT UNTIL 8 PM EDT THIS EVENING…
* WHAT…Flash flooding caused by excessive rainfall is possible. […]
* WHEN…Until 8 PM EDT this evening.
* IMPACTS…Exc