Local tornado warnings are over
Update, 8:10 p.m.:
The tornado warning throughout much of metropolitan Washington has ended. Showers and storms are now moving into the northern and eastern portions of the area, while weakening at least a bit.
The National Weather Service says the air mass north of D.C. is more stable than it was to the south, so the main severe storm risk is dwindling. But some of the rain spurts are still heavy, and will exacerbate any flooding problems.
More showers are possible behind the line of storms, but they will be lighter as cooler air starts moving in, the weather service said.
Update, 7:14 p.m.:
The weather service says the tornado warning is in effect until 7:30 p.m.
The agency said its Dopper radar indicated a severe thunderstorm capable of producing a tornado near Centreville.
Areas affected include Dulles International Airport, South Riding, Herndon, Ashburn and Lansdowne in Loudoun County, the weather service said.
The National Weather Service has issued a tornado warning for areas including Montgomery and Fairfas counties, effective immediately.
Eastern Loudoun County, north central Prince William County, northwestern Fairfax County and Manassas are among the areas effected.
"This is a dangerous and possibly life threatening situation," the alert says.
People are urged to evacuate mobile homes and vehicles immediately. If no shelter is available, people should lie flat in the nearest ditch or other low spot and cover their heads with their hands.
Do not wait to hear or see a tornado before taking action, the weather service advises. Tornadoes that form at night may not be visible, the agency says.