Low pressure passed by to the west as it tracked into the Ohio Valley and Great Lakes on the 18th into the morning of the 19th, before transferring its energy to a coastal low along the Mid-Atlantic Coast. The coastal low moved out to sea later on the 19th.
Canadian high pressure supplied plenty of low-level cold air, but warmer air worked its way in aloft, and this caused a wintry mix of snow, sleet, and freezing rain. Snow and sleet overspread the area on the early morning of the 18th. Snow and sleet changed to a light wintry mix including freezing rain by the evening of the 18th. Precipitation ended as a period of light snow and sleet on the morning of the 19th.
The highest snowfall accumulations (around 3 to 6 inches) were across northern Maryland east of Interstate 81, but west of Interstate 95 where the heaviest precipitation occurred, and temperatures aloft were cold enough for precipitation to start off as snow. However, mostly sleet occurred in the Washington and Baltimore Metropolitan areas, so accumulations were less (around an inch). Snowfall amounts around 2 to 5 inches were reported across northern Maryland near and west of Interstate 81.
Ice accumulation from freezing rain was up to a tenth of an inch for most areas, but around a quarter inch in southern Maryland where warmer air aloft cause more freezing rain vs. snow or sleet.

Winter Storm in FREDERICK, MARYLAND
From 18-FEB-21 04:00:00 to 18-FEB-21 13:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in CARROLL, MARYLAND
From 18-FEB-21 04:00:00 to 18-FEB-21 13:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in NORTHERN BALTIMORE, MARYLAND
From 18-FEB-21 04:00:00 to 18-FEB-21 13:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in NORTHWEST HARFORD, MARYLAND
From 18-FEB-21 04:00:00 to 18-FEB-21 13:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in WASHINGTON, MARYLAND
From 18-FEB-21 13:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Department of Highways

Interstate 81 was closed in the evening due to ice from light freezing rain and freezing drizzle at the Maryland/West Virginia Line. There were numerous cars involved in an accident.

Winter Weather in FREDERICK, MARYLAND
From 18-FEB-21 13:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in CARROLL, MARYLAND
From 18-FEB-21 13:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in NORTHERN BALTIMORE, MARYLAND
From 18-FEB-21 13:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in NORTHWEST HOWARD, MARYLAND
From 18-FEB-21 13:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in CALVERT, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in GARRETT, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in CECIL, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in SOUTHERN BALTIMORE, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in ANNE ARUNDEL, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in CENTRAL AND EASTERN ALLEGANY, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in EXTREME WESTERN ALLEGANY, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in NORTHWEST MONTGOMERY, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in CENTRAL AND SOUTHEAST MONTGOMERY, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in NORTHWEST HOWARD, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in CENTRAL AND SOUTHEAST HOWARD, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in NORTHWEST HARFORD, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in SOUTHEAST HARFORD, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in WASHINGTON, MARYLAND
From 18-FEB-21 04:00:00 to 18-FEB-21 13:00:00 (EST-5)
Reported by: Trained Spotter

Winter Storm in ST. MARY'S, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Trained Spotter

Winter Weather in PRINCE GEORGES, MARYLAND
From 18-FEB-21 04:00:00 to 19-FEB-21 09:00:00 (EST-5)
Reported by: Department of Highways

The ramp from northbound MD-210 to I-495 and I-295 was closed due to ice from freezing rain.