To the state the obvious, the atmosphere is extremely moist. Just walk outside for a few minutes for ground truth.

When a cold front runs into this oppressively humid air this evening, showers and thunderstorms are likely. Nailing down the exact timing of storms is always tricky, but most storms should occur between 4 and 11 p.m. (just a chance of isolated activity before/after) with my favored window between roughly 6-10 p.m. (closer to 6-8 p.m. west of the District, and 8-10 p.m. from the District and points east).

Storm coverage should be most widespread north of the District, and may become somewhat more scattered (hit or miss) south of the District.

“With the energy and stronger shear passing to our north, expect more organized storms/longer-lived storms, and best chance of any severe storms north of the Mason Dixon line,” says Jeff Halverson, Capital Weather Gang’s severe storm expert.

NAM model simulation of storms between 7 and 11 p.m. This is just simulation and the actual timing, coverage and intensity of storms is likely to vary. (

Given the available moisture levels (very high – precipitable water around 1.9-2.0 inches), torrential rain is possible in storms that form. The storms should move along at a decent clip – around 20-25 mph – but rain rates may be high enough to trigger isolated flash flooding.

Thunder and frequent lightning should complement many storms. When thunder roars, go indoors.

The storms may well produce some strong gusts in the 40-60 mph range, and isolated damaging gusts (above 60 mph) cannot be ruled out. But the highest potential for damaging winds and microbursts is into Pennsylvania and New York state.

We’ll keep you posted on the storm threat as the day wears on.

(Capital Weather Gang severe storm expert Jeff Halverson contributed to this post)