UPDATE, 1:50 p.m.: Storms are rapidly developing and intensifying south and west of D.C. Please stay tuned for possible warnings.
UPDATE, 1:30 p.m.: A tornado watch has been issued for western Virginia and western Maryland including Loudoun, Fauquier and Frederick counties. In the watch area:
TORNADOES...HAIL TO 1.5 INCHES IN DIAMETER ... THUNDERSTORM WIND GUSTS TO 70 MPH ... AND DANGEROUS LIGHTNING ARE POSSIBLE
Expect a watch to be issued for areas further east including the DC/Baltimore metro areas soon.
UPDATE, 1:20 p.m: NOAA’s Storm Prediction Center says tornado watch likely to be issued (80 percent chance) for D.C./Baltimore region next one to two hours.
UPDATE, 1:15 p.m.: In addition to placing the D.C., Baltimore region under a moderate risk of severe thunderstorms (rare for this area), the National Weather Service Storm Prediction Center has increased the tornado chance to 15 percent (from 10 percent earlier) within 25 miles of point. Here’s their rationale for bumping up the severe thunderstorm and tornado risk (bold text indicates my added emphasis):
HAVE ADDED A MODERATE RISK IN THE WASHINGTON DC METRO...BALTIMORE AREAS WHERE THE TORNADO THREAT IS EXPECTED TO BE THE GREATEST AND WHERE AN ISOLATED STRONG TORNADO CAN NOT BE RULED OUT. ANY ROTATING STORMS SHOULD ALSO BE CAPABLE OF PRODUCING WIND DAMAGE. AS THE STRONGER LARGE-SCALE ASCENT MOVES ACROSS THE MID-ATLANTIC EARLY THIS EVENING...A WELL-ORGANIZED LINEAR MESOSCALE CONVECTIVE SYSTEM IS EXPECTED TO BECOME THE DOMINANT CONVECTIVE FEATURE WITH AN ENHANCED WIND DAMAGE THREAT PRESENT ACROSS A LARGE AREA OF THE MID-ATLANTIC.
See related post with more details and timeline: Breaking down today’s thunderstorm threat for Washington, D.C. and Baltimore region
UPDATE, 12:45 p.m.: Storms are firing up west of the District in northern Fauquier, western Prince William, and southern Loudoun counties. These are moving northeast and should move into western Montgomery and Frederick county in the next hour. They are not severe at the moment, but contain some heavy downpours. As the general tendency should be for storms to intensify, we will keep you apprised of any watches/warnings.
UPDATE, 12:30 p.m: From the National Weather Service Storm Prediction Center:
CATEGORICAL UPGRADE TO MODERATE RISK WILL BE INCLUDED WITH THE 1630 UTC [12:30 PM ET] DAY ONE CONVECTIVE OUTLOOK ACROSS NORTHEASTERN VA...A LARGE PART OF MD...THE DISTRICT OF COLUMBIA...A SMALL PART OF THE EASTERN PANHANDLE OF WV...AND SOUTH CENTRAL PA.
DISCUSSION...LATEST OBSERVATIONAL AND MODEL OUTPUT WARRANT AN UPGRADE TO MODERATE RISK...
It is rare for moderate risk outlooks in the D.C. area - maybe once or twice per year, on average...