Areas of Heavy Rainfall Likely Overnight through Friday

An area of low pressure will approach the Washington Region tonight before crossing our area on Friday. The combination of a humid air mass in place and a weak boundary draped across the area increases the threat of flash flooding where thunderstorms move over the same areas.  The image below, courtesy pivotal weather is from the latest European forecast model which shows the area of low pressure sliding out of the Ohio Valley this evening and into the DC Region on Friday.

Potential Rainfall Totals

Much of the region could pick up at least a half-inch of rainfall, however training thunderstorms could drop over two inches of rain in spots leading to flash flooding concerns. The eastern slopes of the Blue Ridge and parts of Frederick county Maryland are currently in a “moderate drought” and could use the rainfall, whereas the interstate 95 corridor, closer to DC and Baltimore has received hefty rainfall totals of late and thus are not currently in drought conditions.

The upcoming weekend is looking unsettled with disturbances sliding across our area helping to aid in the development of afternoon thunderstorms. Those of you who are currently in a moderate drought should continue to see some additional relief in the form of beneficial rainfall through the middle portion of next week.

Afternoon Damaging Wind Threat for DC Region

The Washington Region remains under a “slight risk” for severe thunderstorms this afternoon. Increasing lapse rates out ahead of an approaching upper level trough along with ample daytime heating will produce the ingredients necessary for storms capable of producing damaging winds in excess of 60 – 70 mph. Cloud to ground lightning, torrential rain and hail are also possible in these storms.

The high resolution NAM model (image above courtesy Tropical Tidbits) predicts that a line of thunderstorms will approach the Shenandoah Valley around 2pm, pushing eastward into the Washington Region between 3 and 6 pm. I would not be surprised to see a Severe Thunderstorm Watch issued for our region during the early afternoon hours.