The Hagerstown Almanack Monthly Weather Column

Cumberland, MD. November 30, 2024 - As you read this column during the second half of the Thanksgiving holiday weekend, you are probably reminded of winter in a sincere, but harsh way. The cold temperatures, wind and snow flurries probably have you blasting the heat!

Following a top-10 warmest November on record, Mother Nature has big tricks up her sleeves for the final month of the year. First of all, La Nina will be a moot point in our weather pattern. Instead, the configuration of ocean temperature anomalies in the Indian and West Pacific Ocean are indeed driving the pattern now underway in western Maryland.

In a typical La Nina pattern with a negative Pacific Decadal Oscillation, the West would be cold and snowy and the East would be warmer than average. However, the Tropical Northern Hemisphere pattern is our guide for December. First identified in 1986, it’s a predominant pattern that when in full force sticks around through February. The current positive phase allows cold air to push into the central U.S., and frequently move into western Maryland in the wake of cold fronts.

The Tropical Northern Hemisphere Pattern switched to a positive phase late this month and the best two matching years in which this occurred, include December 1988 and December 2015. The month’s coldest temperatures (single digits to mid-20s) in both years occurred between December 6 and 12 while the warmest temperatures (60s) greeted the region between December 20 and 28.

Garrett County is accustomed to snow showers in the wake of cold fronts and the first half of the month will deliver these periodic episodes. The pattern favors ski resorts like Wisp Resort, Whitetail and even Liberty the ability to open on time. Historical trends of this pattern support a cold, but not necessarily snowy period. Most of the snow accumulation east of Route 36 will occur during the pattern transition to a warmer second half of December.

The time period to keep an eye out for snowfall is December 13 and 20. None of the similarly matched December’s produced a large Nor’easter with a crippling snow, but rather a series of smaller winter storms with up to 4 inches of accumulation in Cumberland and 7 inches of snow in Oakland.

This is also the time period where the pattern will switch to a milder regime with likely above average temperatures. Therefore, the prospect of a White Christmas is less than 30% in Allegany County. However, that chance is much higher for Garrett County. There is a 60% risk for 1 inch of snow to remain on the ground the morning of December 25 thanks to the topography aligning with the windward slopes of the Appalachians during December’s first half high snow shower and cold weather frequency period. Plus, snow will occur during the pattern transition, so just enough should stick around for 1 inch to remain on the ground Christmas morning here.

As of November 25, all five of the Great Lakes are the warmest they have been since 1995, but Lake Erie has the biggest temperature anomaly of all of them. This is very important because the colder the temperatures aloft become during the cold spell through mid-December, the better chance for snow showers to bring more efficient accumulation downwind of the Great Lakes into Garrett and western Allegany County. Thundersnow even becomes possible when extreme temperatures are observed between warm Great Lakes water and Arctic air that sweeps over the Great Lakes.

December will likely yield warmer temperatures along the West Coast into the northern Rockies and colder than average temperatures east of the Rockies to the Appalachians. The southern Plains to Deep South will see temperatures near to just above average.

The good news about the drought is the cold weather slows the evaporation process, so despite a likely drier than average first half of December, the drought should remain the same. The mid-December pattern transition will likely yield a storm that will help the drought. By the end of December, southern Garrett and Allegany County should improve from an extreme to a moderate drought.

As the cold air mass sweeps through the region over the next two weeks, remember to keep cabinet doors open in order to avoid busted water pipes, keep sufficient air in your car tires because cold weather results in abnormally low tire pressure and keep the hand moisturizer out because the indoor humidity will drop very low during these cold days!

 

Chad Merrill is a Cumberland native and meteorologist who not only serves as the Hagerstown Town and Country Almanack weather prognosticator but has previously been meteorologist with WDVM (formerly known as NBC25) in Hagerstown and at WJAC-TV in Johnstown, Pennsylvania, and most recently, was named chief meteorologist at WOAY-TV in Oak Hill, West Virginia. After a rigourous evaluation,  Merrill  was awarded the National Weather Association (NWA) Seal of Approval.  According to the association, only 1,045 meteorologists currently hold the NWA Seal of Approval.  In April, 2023, Merrill, was inducted into the prestigious Marquis Who's Who Biographical Registry!  Feel free to contact him at cmweather24@gmail.com or 240-285-8476.