The streak of soupy days ceases Sunday, but a line of severe thunderstorms Saturday may be the price to pay for the incoming rush of autumn air.
The National Weather Service’s Storm Prediction Center (SPC) says there is a slight risk of severe thunderstorms over the Baltimore and Washington, D.C. metro area and a moderate risk of severe storms north of the Mason Dixon line. It warns: “Potentially significant damaging wind event is expected in the northeastern U.S. Saturday.”
SPC says there is a 30 percent chance of severe weather within 25 miles of a point in the D.C./Baltimore region and up to a 45 percent chance from southeast Pennsylvania into central New England.
Generally, the storms should pack less of a punch in the mid-Atlantic compared to New England. Still, the National Weather Service (NWS) office in Sterling, Va., covering DC/Baltimore, cautions:
CONFIDENCE IN SEVERE WEATHER INCREASING FOR THE DAYTIME HOURS SATURDAY.
It notes the main potential hazard is damaging winds but warns there is also “some tornado risk”. Hail is also possible.
The trigger for the potential intense squall line is a strong cold front that will charge through the mid-Atlantic and Northeast Saturday afternoon, close to the time temperatures are hottest, maximizing available instability.
While clouds may limit the instability some, the NWS says “this is expected to be more than compensated for by strong forcing from the front.”
The most likely timing for storms is between about 4-10 p.m. Saturday in the D.C./Baltimore region, but adjustments to this window are possible.
The elevated risk of damaging winds north of the mid-Atlantic is tied to strong winds at high altitudes, SPC says:
OF PARTICULAR CONCERN IS THE EXPECTED MID LEVEL JET THAT SHOULD INTENSIFY AS IT EJECTS ACROSS WRN PA TO SPEEDS IN EXCESS OF 70KT [80 MPH] OVER UPSTATE NY.
Some tornadoes are possible in this region as well.
For the Northeast, this is the third time SPC has issued a moderate risk on record (dating back to 1998) during the month of September (hat tip @jimmyc42 on Twitter)