December 5, 2005 Winter Storm
Preliminary - Updated
...The December 5th Storm across portions of Virginia and Maryland was the 1st notable winter
storm to affect the Wakefield, VA county warning area for the 2005-2006 season...
...The storm was characterized by significant differences in precipitation amounts and precipitation types
over short distances...
...Portions of central and east central Virginia and the lower eastern shore of Maryland
received significant accumulations of snow and sleet.
A relatively early season storm brought snow and sleet to portions of central and
east-central Virginia and the lower eastern shore of Maryland, with all rain
for southeast Virginia and northeast North Carolina throughout the day of the
5th, continuing into the early morning hours of the 6th. After a balmy day Sunday
the 4th, when temperatures soared into the mid 60s at Richmond and Norfolk, and
57 F at Salisbury, Maryland, the event gradually developed during the late evening
hours of December 4th, as developing low pressure over the deep south combined
with colder air filtering down from the northwest. Widespread rain began after 1 am
on the 5th as temperatures dropped into the lower 40s at Farmville and Richmond.
The rain briefly mixed with sleet before changing to mainly snow with occasional
sleet after 4 am for areas along and north of a Farmville to Richmond line. By
afternoon, this line extended northeastward through the northern Neck to a position
near Wallops Island, with areas along and to the north continuing with mainly snow,
mixed at times with sleet, while areas to the south had moderate to heavy rain. The
rain/snow line moved a bit farther northward during the evening, then back south
as the precipitation ended as snow or rain showers early on the morning of the 6th.
This snow, sleet, and rain event was associated with a pattern of warm advection through the low
to mid layers of the atmosphere. This pattern is characterized by a relatively simple mean
sea level pressure pattern where a fairly weak surface low tracks northeastward across
Georgia and the Carolinas, with a surface high pressure center located to the north. Unlike
the "Miller B" storms when cold air is already locked in place across the mid-Atlantic, this type
of storm begins with relatively warm temperatures that drop as the storm initiates, and cold air
continually filters in from the north or northwest. With this particular storm, the surface low
developed in the Gulf of Mexico in response to an amplifying mid level trough moving into the
southern Plains states. The low then tracked northeastward and was located near Athens, GA
by early Monday afternoon, and was off the North Carolina and Virginia coast by early Tuesday
Precipitation began as very spotty areas of light rain during the evening of Sunday the 4th, with most
locations clouding up, but remaining dry. The precipitation shield then became more
widespread after midnight, as a strong core of the upper jet stream (located about 35,000 feet
above the ground) approached the region from the southwest. In addition, winds in the low levels
up through about the 850 mb layer (roughly 5,000 feet above the ground) became convergent
across southern Virginia, with southerly flow south of this line converging with northerly flow
moving southward from Pennsylvania. The convergence in the low levels combined with
divergence aloft with the right entrance region of the upper jet allowed sufficient uplift to develop.
Above the 850 mb layer, winds were generally southwest out ahead of the approaching trough,
allowing for ample moisture feed from the Gulf of Mexico.
By daybreak and throughout the day of December 5th, moderate to occasionally heavy precipitation
continually tracked along the zone of low-level convergence from near Danville, VA
east-northeastward into Accomack county on the Virginia eastern shore. Meanwhile the surface
high to the north kept somewhat drier air in place across Louisa and Fluvanna counties, keeping
the snow there relatively light. Radar imagery during the mid-morning hours depicts the heaviest
line of precipitation, mainly sleet from just south of Farmville to near Chester and Hopewell, VA.
Just north of this line, Richmond was reporting moderate snow, while just south it was all rain.
This setup more or less continued through the afternoon hours.
By late afternoon and early evening, much of the region from Amelia County eastward to Richmond and
into the northern Neck had received 3 to 4 inches of snowfall. Radar and satellite imagery at 6 pm
showed that the back edge of the precipitation had moved to near Farmville and Danville.
However, the storm was not over, as the main surface low at this point was still located in South
Carolina. By late Monday night into early Tuesday morning, the surface low strengthened offshore
and a deformation zone in the mid levels formed across Virginia and Maryland, enabling wrap
around moisture to bring additional snow accumulations to Louisa, Caroline, and Hanover counties
in central Virginia, and portions of Maryland from Salisbury westward. At Ocean City enough low
level warm air came in from the Atlantic to turn the snow over to rain, limiting accumulations along
the immediate coast.
Snow / Sleet Accumulation Map
The corridor of heaviest snow and sleet accumulation fell in a fairly narrow band from just north of
Farmville up to Louisa eastward across the Richmond metro area into the northern Neck and
up through inland portions of the Maryland eastern shore, generally from Salisbury west to
Cambridge. Most locations in this band received 3 to 4 inches of snow and sleet, with locally
up to 6 or 7 inches near Tappahannock and across northern Dorchester County in Maryland. As is
often the case, there was a sharp cutoff of accumulation near the rain/snow line, which in this
case set up across the southern suburbs of metro Richmond. The Richmond Airport recorded a
total of 4.4" of snow (and sleet) for the event, while Petersburg, just over 20 miles to the south
received about half an inch.