PM Update: Patchy fog possible late tonight, then warm again Friday

Dulles Airport pulled off a 40-degree swing in temperatures today, from a low of 32 to a high of 72. We can thank dry air, a mild flow from the south, and a temperature inversion for much of it. Plentiful sunshine didn’t hurt. Many spots locally reached for or hit 70 this afternoon and we’ll do it again Friday despite some additional clouds. A cold front is headed our way for Friday night. It won’t offer much of any relief to the recent dry and fire-fueling conditions, but it will turn things cooler for the weekend.

Through Tonight: We should see varied temperatures again tonight. Some spots will be into the mid-30s or so, while much of the area will stay in the 40s under mainly clear skies. Winds will be light and variable. Some patchy fog could develop late.

Tomorrow (Friday): Patchy fog will dissipate early. More clouds will be around compared to today, but enough sun should be available to deliver temperatures striving for 70 once more. A couple showers are possible Friday night with a cold front, but nothing worth thinking much of.

See David Streit’s forecast through the weekend . And if you haven’t already, join us on Facebook and follow us on Twitter and Instagram . For related traffic news, check out Gridlock .

Temperature inversion: It was a factor in today’s rapid warming and the trapping of smoke in the Shenandoah Valley last night. Rather common in the cold season, inversions occur when comparatively cold air settles close to the ground while a warm layer sits on top of it.

In light winds, this can trap air — or smoke — especially in valleys. When it breaks in the morning as the sun’s rays help mix the air, it can allow for significant temperature spikes. Today’s was rather impressive, with around 25 degrees in warming over the lowest third of a mile off the ground, as shown below.