4:55 p.m. update: The Tornado warning in southern Maryland has been discontinued.
This is our last update in this post. We expect additional heavy rain and possible thunderstorms this evening, a few of which could be severe. For the latest, see our PM Update: Flood warnings through this evening, outside chance of severe storms; nicer Thursday
4:49 p.m. update: The tornado warning in Southern Maryland (see 4:30 p.m. update) remains in effect until 5 p.m. Radar continued to indicate the possibility of a tornado. It 4:39 p.m., the parent thunderstorm was positioned about 5 miles north of the Wicomico River, moving northeast at 25 mph. In the possible path: Charlotte Hall and Mechanicsville.
4:30 p.m. update: Tornado WARNING issued for central Charles, NW St. Mary’s counties til 5 p.m. Radar indicated a rotating thunderstorm near Colonial Beach moving northeast at 30 mph. The rotation in this storm does not appear particularly strong, but – in an abundance of caution – take cover immediately if in the warned area (see area outlined in red polygon below).
LATEST RADAR!! pic.twitter.com/7eB3G5UDMZ— SouthernMD WX & NEWS (@SOMDWxNews) April 30, 2014
From 3:11 p.m.: While metropolitan Washington and Baltimore copes with flooding rain, it’s unclear whether severe thunderstorms will pose an additional hazard as we get into tonight.
The National Weather Service’s Storm Prediction Center has nudged the zone favorable for severe thunderstorms and possible tornadoes just south and east of the District. Areas east of I-95 and especially towards southern Maryland and central Virginia have the highest potential for nasty storms this evening.
Already, a tornado watch has been issued for southeast Virginia and northeast North Carolina, including Richmond and Norfolk through 7 p.m. But even there, this is a lower-end tornado watch. SPC says there is just a 40 percent chance of two or more tornadoes in the watch area.
The limiting factor for tornadoes and severe weather in the immediate metro area is a lack of instability. Although warmer air has oozed into the region (temperatures have risen into the 60s, except 50s in our western suburbs) – displacing the cool wedge that had been in place, cloudy and rainy conditions have prevented the sunshine that could help fuel big storms.
But the National Weather Service forecast office in Sterling warns we shouldn’t completely let our guard down, as enough warm air could still be drawn northwestward to destabilize the atmosphere this evening:
DESPITE THE CLOUD COVER. SHEAR PROFILES REMAIN QUITE FAVORABLE FOR SEVERE THUNDERSTORMS WITH THE PRIMARY THREATS BEING DAMAGING WIND GUSTS AND ISOLATED TORNADOES. THE MAIN UNCERTAINTY IS WHETHER OR NOT STORMS CAN GET ROOTED WITHIN THE BOUNDARY LAYER…AND THAT IS MOST LIKELY IN THE WARM SECTOR NEAR AND EAST OF THE I-95 CORRIDOR LATE THIS AFTERNOON. HOWEVER…THE COLD FRONT WILL BE VERY SLOW TO MOVE THROUGH THE AREA. THEREFORE…SEVERE THUNDERSTORMS ARE POSSIBLE ACROSS MUCH OF THE CWA TONIGHT AS TEMPS/DEWPOINTS INCREASE WITH THE SOUTHERLY FLOW AHEAD OF THE COLD FRONT.
“Our region’s threat likely will be very late today i.e. this evening, even into the overnight,” says Jeff Halverson, CWG’s severe weather expert.
In closing, we do not believe the risk of tornadoes and/or damaging thunderstorm winds is especially high, but it also cannot be ruled out (particularly in our southern suburbs) and we will keep you apprised of any changes to the forecast as well as watches/warnings issued.