The National Weather Service issued a snow and sleet advisory for Monday afternoon and evening for a sizable swath of the Baltimore area, warning motorists that roads may be slippery and visibility limited.
The weather service predicted an accumulation of between one and three inches of snow in parts of the region.
Snow began falling earlier in the afternoon in some areas, and drivers slowed along area roadways as flakes filled the sky.
Sandra Dobson, a State Highway Administration spokeswoman, said 38 drivers and other personnel were keeping an eye on the roads, and began salting in northern Baltimore County shortly after 4 p.m.
The NWS forecast change, issued around 1:15 p.m., predicts first snow in the early afternoon, followed by a mix that includes sleet and rain, tapering off around 8 p.m. for Howard, Carroll, Harford and northern Baltimore counties. Temperatures will drop into the lower and middle 30s.
Across much of the Baltimore region, between a half-inch and 11/2 inches had fallen by Monday evening, according to the weather service.
Dobson said drivers should be on the lookout for slick areas, and warned bridges and ramps could become icy.
The change in the Christmas Eve forecast comes on the heels of winter weather advisories for Carroll and Frederick counties, where up to an inch of snow is expected, as well as much of Western Maryland.
The forecast for the Baltimore area includes Columbia, and extends into northern Montgomery County.
A winter weather advisory was issued for Washington County and much of Allegany County for Monday until midnight. The National Weather Service said snow is expected to begin early Monday afternoon, mixing with sleet and rain at times, followed by light freezing rain or freezing drizzle later in the afternoon and evening. An accumulation of an inch or two of snow and sleet and a trace of ice are expected. High temperatures will be in the mid to upper 30s, but then fall close to freezing. Roads may be slick.