Greetings, Western Maryland and the Potomac Highlands. At the end of each month, I will be providing an overview ahead for next month’s expected weather pattern. I will provide insight into the leading factors governing the weather for the next 30 days.
More specific details on the day-to-day weather can be found in the latest Hagerstown Town and Country Almanack, where I serve as the weather prognosticator.
December is just around the corner and that marks the start of meteorological winter, traditionally the three coldest months of the year. For 2020’s final month, several factors are lining up to bring a few cold blasts and the first accumulating snow east of the Allegheny Plateau.
The variable driving our overall weather pattern this winter is a moderate to strong La Nina and a likely strong polar vortex. In a La Nina winter coupled with a strong polar vortex, very few cold outbreaks slam the eastern U.S. Instead, a typical winter storm track is across the Northwest into the Plains and up the Ohio Valley. December and March usually end up being the snowiest months for the Potomac Highlands in a La Nina winter.
For snow lovers in Western Maryland and Potomac Highlands, a common storm track that produces several inches of snow in the Potomac Highlands and downwind of the Alleghenies is focused south across the Tennessee Valley and southern mid-Atlantic. Our biggest snowstorms develop along the Gulf Coast then sweep up Interstate 95.
Within December’s first week, two storm systems tracking west of the Alleghenies will bring rain followed by lake-effect and mountain-enhanced snow and strong wind. Western Allegany and Garrett County will see several inches of snow in the storm’s wake with the first coating of the season east of the plateau. A stronger storm system closer to December’s midpoint will likely bring moderate rain amounts. In its wake, a favorable wind direction for lake-effect and mountain-enhanced snow showers will bring a few inches to the Alleghenies with a dusting east of the plateau.
Following a few days of chilly but seasonable December temperatures, a somewhat milder pattern will unfold as mid-December arrives. Another weather system tracking west of the Alleghenies will bring wet snow that will transition to rain leading up to Christmas Day with snow showers in its wake across the Alleghenies.
As we approach Dec. 25, what are the prospects of a White Christmas? NOAA defines a White Christmas as 1 inch or more of snow on the ground during any part of Christmas Day. Historically, our chances range from 25% in Cumberland to 50% in Garrett County. For this year, I only expect the Alleghenies west of Savage Mountain will see 1 inch of snow on the ground on Christmas Day. Dec. 25 will likely be brisk but seasonable with 40s, except 30s on the Allegheny Plateau.
The weather pattern will once again turn active to conclude December. The month’s final storm system will follow the typical La Nina winter storm track but there will likely be enough cold air trapped at the surface for snow, sleet and freezing rain at the onset. In the storm’s wake, snow showers will occur west of the Allegheny plateau and flurries east of the plateau. This will be followed by a chilly and brisk start to 2021 on New Year’s Day. On the tail end of each of these December systems expect a burst of occasionally gusty winds.
I see slightly less snow than average in December. Cumberland averages 5 inches and Oakland typically sees 15-20 inches of snow in December.
When will the warmest weather occur in December? Likely the second week of the month and the 16-20th will bring the mildest temperatures.
When will the coldest weather occur in December? The first week of the month and again between December 13-15 and 29-31 will feature the biggest chill.
We hope you enjoy reading my weather predictions for the Potomac Highlands each month. For more information on the weather forecasts through the end of 2021, check out the 2021 Hagerstown Town and Country Almanack. Have a great December and holiday season and I’ll fill you in on January’s weather trends in a few weeks.
Chad Merrill is a Cumberland native and meteorologist who serves as the Hagerstown Town and Country Almanack weather prognosticator and senior meteorologist at Earth Networks in Germantown. Merrill previously was a meteorologist with WDVM (formerly known as NBC25) in Hagerstown and WJAC-TV in Johnstown, Pennsylvania. Merrill can be reached at 240-285-8476 or by email at firstname.lastname@example.org.