Quite often when I get my worst fog events, the MD NWS has the headline like this am.
DENSE FOG ADVISORY IN EFFECT UNTIL 8 AM EDT THIS MORNING...
* WHAT...Visibility of a quarter mile or less in dense fog.
* WHERE...Portions of central, north central, northern, and western
Maryland, northern Virginia, and eastern West Virginia.
* WHEN...Until 8 AM EDT this morning.
* IMPACTS...Low visibility could make driving conditions hazardous.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If driving, slow down, use your headlights, and leave plenty of
distance ahead of you.