Rain began falling hard in Reston about 2 p.m. and could continue through most of the afternoon and evening.

The National Weather Service says rainfall rates of “up to two inches per hour” may cause flash flooding in some already-saturated areas.

The NWS has issued a Severe Storm Watch for most of the Washington, D.C., area through 9 p.m.

Fairfax County and most neighboring areas are also under a Flash Flood Watch until 10 p.m. tonight.

From NWS:

TROPICAL MOISTURE WILL REMAIN OVER THE AREA THIS EVENING. AFTER A COUPLE OF PREVIOUS OF HEAVY SHOWER AND THUNDERSTORM ACTIVITY…ONLY ONE TO TWO INCHES OF ADDITIONAL RAINFALL WILL BE NEEDED IN TARGETED AREAS TO PRODUCE FLASH FLOODING. SHOWERS AND THUNDERSTORMS ARE LIKELY EARLY THIS EVENING ACROSS THE AREA…ESPECIALLY EAST OF THE BLUE RIDGE TO THE CHESAPEAKE BAY.

RAINFALL RATES IN HEAVIER SHOWERS AND THUNDERSTORMS MAY EXCEED 2 INCHES PER HOUR IN TARGETED AREAS THAT RECEIVE TORRENTIAL RAIN FOR LONGER THAN 30 MINUTES.

FLASH FLOODING MAY BEGIN QUICKLY. BE AWARE OF LOW AREAS THAT MAY FLOOD. NEVER CROSS ROADS THAT ARE FLOODED. TURN AROUND DON’T DROWN. PRECAUTIONARY/PREPAREDNESS ACTIONS… A FLASH FLOOD WATCH MEANS THAT CONDITIONS MAY DEVELOP THAT LEAD TO FLASH FLOODING.

Photo: Reston Now file by Bahmad Farzad 

The National Weather Service says Northern Virginia residents should prepare for heavy rain and possible flooding Thursday and Friday.

The NWS has issued a flash flood watch from Thursday afternoon through Friday for Fairfax County and most of Northern Virginia.

The NWS says showers and thunderstorms with periods of heavy rain will begin this afternoon and continue through Friday morning. Two to three inches of rainfall is expected. Flash flooding is possible, especially along small rivers and streams.

A flash flood watch means that conditions may develop that lead to flash flooding.

File Photo Credit: Ed Schudel