Some of the cameras show either a lot of fog or a lot of smoke. Earlier it really didn't look like fog because of how quick it was moving and it was not spread out like fog would be.
Live Webcam 1 - Reagan National Airport - Washington D.C.
Live Webcam 2 - 4K - Reagan National Airport - Washington D.C.
Live Webcam 3 - 4K - Reagan National Airport - Washington D.C.
Cam 4 - defo billowing smoke rising up at side of ATC tower.