A dense fog advisory was issued Sunday night for the entire Baltimore region, with conditions expected to continue through Monday morning, according to the National Weather Service.
The fog first covered the Eastern Shore and crept across the Chesapeake Bay into Anne Arundel, Calvert and St. Mary's counties before the weather service expanded its advisory just before 10:45 p.m. to include most of the rest of the state, including Baltimore City and Baltimore, Carroll, Howard and Harford counties.
Visibility was expected to be less than a quarter of a mile in the affected regions, as a stationary front with northeast winds pulls moisture across the region, the NWS said.
The Baltimore-Washington NWS office issued an advisory for Anne Arundel, Calvert and St. Mary's counties.
"Right now we're pretty confident with that area but we might have to extend that more to the west and north in the morning hours, impacting the Washington, D.C., and Baltimore regions," said Heather Sheffield, a NWS meteorologist. "We're going to see whether conditions get worse as the night continues."
Sheffield said she was keeping an eye late Sunday on the fog's northeastern path across the state.
By late Sunday, the fog advisory applied from Northern Virginia through Washington and north to Harford, and across the Eastern Shore west to Frederick.
The advisories were in effect through 9 a.m. Monday.