A cold front accompanied by a squall line will approach the Washington Region late this evening. Damaging wind gusts are possible, especially just south and west of the Washington Region across north-central Virginia and the Shenandoah Valley. A strong low-level jet stream and wind shear (winds changing direction and speed with altitude) would typically indicate the potential for severe thunderstorms (some containing a tornado threat) however the missing ingredient will be instability (CAPE) as the sun will have set well before the arrival of the cold front. Regardless, the Storm Prediction Center has placed the DC Region under a marginal risk for severe thunderstorms with damaging wind gusts being the primary threat between 9 PM and 1 AM late this evening.
Timing the arrival of the squall line (a line of convection containing gusty winds and heavy rainfall):
The image below is from the North American Model showing one future-cast simulation of the squall line moving through the immediate Washington Area between 10 PM and 1 AM. Rainfall amounts of a quarter inch to three-quarters of an inch are possible with this fast-moving line of storms.
Tropics May Become Active Next Weekend:
European Ensembles show a cluster of “L’s” (representing the possible location of an area of low pressure) from western Cuba to near south Florida and the northern Bahamas on Saturday afternoon.
As a strong trough of low pressure digs southward into the northern plains late this weekend we will need to closely monitor the east coast of the United States as a tropical system may ride northward out ahead of a strong cold front. Details of how these features could interact are murky at best, but there is the potential for a significant coastal storm and/or tropical system with a blast of arctic air infiltrating our region around Halloween.
European Ensembles Sunday evening:
Notice the cluster of “L’s” just off the Mid-Atlantic coast
The latest Climate models still indicate a cold end to October continuing through at least the first few days of November.
I am hopeful we can get our first hard freeze to kill the mold spores and kick off the fall foliage which will be peaking late this year.