A disturbance in the northern branch of the jet stream was able to phase with low pressure in the southern branch of the jet stream over the Southeast Coast on the night of the 18th. These two systems combined to develop a strong area of low pressure that slowly track up the Mid-Atlantic Coast during the 19th. The low was able to tap into moisture from the Gulf of Mexico and the Atlantic Ocean causing copious amounts of precipitation to develop. High pressure to the north kept plenty of cold air in place causing the precipitation to fall in the form of snow.

Winter Storm in CARROLL, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts were reported between 19 and 20 inches across the county.

Winter Storm in PRINCE GEORGES, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 14 and 19 inches were reported across the county.

Winter Storm in MONTGOMERY, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 17 and 24 inches were reported across the county.

Winter Storm in ST. MARY'S, MARYLAND
From 18-DEC-09 17:00:00 to 19-DEC-09 21:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 14 and 16 inches were reported across the county.

Winter Storm in WASHINGTON, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 16 and 21 inches were reported across the county.

Winter Storm in EXTREME WESTERN ALLEGANY, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Snowfall was reported between 14 and 17 inches across the western portion of the county.

Winter Storm in HARFORD, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 17 and 19 inches were reported across the county.

Winter Storm in CENTRAL AND EASTERN ALLEGANY, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall was reported between 14 and 17 inches across the central and eastern portion of the county.

Winter Storm in ANNE ARUNDEL, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 15 and 22 inches were reported across the county.

Winter Storm in SOUTHERN BALTIMORE, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 15 and 21 inches were reported across most of southern Baltimore County.

Winter Storm in FREDERICK, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 19 and 23 inches were reported across the county.

Winter Storm in NORTHERN BALTIMORE, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 15 and 21 inches were reported across most of northern Baltimore County.

Winter Storm in CALVERT, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 18 and 20 inches were reported across the county.

Winter Storm in HOWARD, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 17 and 23 inches were reported across the county.

Winter Storm in CHARLES, MARYLAND
From 18-DEC-09 19:00:00 to 19-DEC-09 23:00:00 (EST-5)
Reported by: Trained Spotter

Snowfall amounts between 14 and 25 inches were reported across the county.