UPDATE 11:00 a.m.: NOAA’s Storm Prediction Center says a severe thunderstorm watch may become necessary late this morning or early this afternoon. Whereas severe hail is a concern to our northwest into SW Pa., damaging winds become the concern this afternoon as storms edge closer to our region. Excerpt:
MARGINALLY SEVERE HAIL WILL REMAIN POSSIBLE ON AN ISOLATED BASIS THIS MORNING ACROSS WESTERN PA TO ADJACENT PORTIONS OF NORTHERN WV/MD/VA. WITH TIME...A DAMAGING WIND THREAT SHOULD BECOME MORE OF A CONCERN INTO THE AFTERNOON.
From 10:18 a.m.: NOAA’s Storm Prediction Center (SPC) cautions there’s a slight risk of severe thunderstorms for the central and western portions of the mid-Atlantic into the Ohio Valley this afternoon and evening. This includes the D.C. metro region along and west of I-95.
The primary threat is damaging wind gusts in excess of 50-60 mph. Heavy downpours, hail, and lightning are also possible in storms that form. An isolated tornado is unlikely, but cannot be ruled out.
The most likely timing for storms is between about 3 and 7 p.m. Storm coverage is likely to be scattered, meaning some areas will get hit harder than others, and some none at all. The odds of storms in any particular location are about 30-50%. Odds are highest to the northwest and lowest east of D.C., especially towards the Chesapeake Bay.
Model simulations indicate the storms will develop to our north in Pennsylvania, and will then sink southeastward.
The trigger for the storms is an approaching cold front. Warm air ahead out of it and sunshine is likely to destabilize the atmosphere as the front draws closer, fueling potential storm development. Here’s the technical breakdown from SPC:
WATER VAPOR IMAGERY SHOWS A LOW AMPLITUDE SHORTWAVE TROUGH MOVING ACROSS THE GREAT LAKES REGION. THE ASSOCIATED SURFACE COLD FRONT CURRENTLY EXTENDS FROM NY/PA INTO SOUTHERN IND.
EARLY VISIBLE SATELLITE IMAGERY SHOWS THAT AMPLE SUNSHINE WILL OCCUR AHEAD OF THE FRONT ACROSS THE OH VALLEY AND MID ATLANTIC STATES. MEANWHILE... STRONG SOUTHWESTERLY LOW LEVEL WINDS WILL HELP TO TRANSPORT 50S DEWPOINTS OVER THE TN VALLEY INTO THE MID ATLANTIC REGION. THE END RESULT WILL BE AN AXIS OF MODERATE AFTERNOON INSTABILITY EXTENDING FROM CENTRAL PA/VA INTO TN/KY.
MOST MODEL SOLUTIONS SUGGEST THAT SCATTERED SHOWERS AND THUNDERSTORMS CURRENTLY OCCURRING OVER NY/PA WILL BUILD SOUTHWESTWARD WITH TIME AND INTENSIFY LATER TODAY. STEEP LOW LEVEL LAPSE RATES...SUFFICIENT CAPE [CONVECTIVE AVAILABLE POTENTIAL ENERGY]...AND RATHER STRONG LOW/MID LEVEL WINDS WILL PROMOTE A FEW ORGANIZED STORMS CAPABLE OF LARGE HAIL AND DAMAGING WINDS. THE STORMS SHOULD BEGIN TO DIMINISH SOON AFTER SUNSET.
We will have storm updates this afternoon as needed. This is unlikely to be a major severe weather outbreak, but a few locations could experience damaging wind gusts.