If you’re one of the many people who need a little cold weather to set the mood for the Christmas season, you may be in luck. It appears that a serious blast of cold air is headed for Tennessee next week.
It has been a warm fall in East Tennessee, and most meteorologists are calling for a very warm winter, overall. But it looks like the first week of December is going to be an exception, after temperatures extend into the 60s for Thanksgiving and the holiday weekend.
After a cold front swings through late Sunday or early Monday, stark changes will be in store. Some models suggest that the temperature could be near 50 degrees around midnight Sunday night, falling into the 20s by Monday afternoon. If leading models are to be believed, we may not get above freezing on Tuesday, either.
How the pattern progresses from there remains in doubt. Some models show milder — though still chilly — temperatures returning for the second half of the work week. Others show a replenishing shot of cold air with a secondary storm system that could actually put down accumulating snow over parts of the region.
Whether an actual winter storm threat pans out for late next week remains in question — and is probably unlikely strictly from a climatological perspective, given that we’re only going to be in the first few days of December — but there is also a possibility of seeing some snow showers on Monday, if wrap-around moisture develops in the cold northwest flow behind the departing frontal system.
For now, forecasters aren’t quite ready to bite on the possibility. The National Weather Service is forecasting a high of 43 with a 30% chance of showers in Oneida on Monday. And, in its forecast discussion, the NWS only vaguely mentions the potential for colder temperatures. But if the likeliest scenarios pan out, that high of 43 on Monday will occur at midnight, with much colder temperatures during the day.
The science behind the probability of colder air lies primarily in the various teleconnections that meteorologists track. The North Atlantic Oscillation (NAO), which measures storminess in the northern Atlantic Ocean, has been predominately positive since early October. The Arctic Oscillation, a similar measurement from the Arctics region, has also been predominately positive since early October, while the Pacific North American ridge index, a measure of ridging in the eastern Pacific Ocean, has been predominately negative for the past several weeks. All three indices are set to reverse by early next week. The combination of a negative NAO, a negative AO and a positive PNA is typically a signal that cold air is looming in the eastern U.S.
Meanwhile, a strong low pressure system appears poised to develop in the western Gulf of Mexico over the weekend and travel up the eastern side of the Appalachians, which will help serve as a catalyst to pull in the much colder air that is being unleashed.
If some model runs are correct, the cold air will exit nearly as quickly as it arrives, with no sustained troughing pattern in the eastern U.S. to hold it in place. Other model runs depict a secondary storm system forming over the Gulf Coast by the middle of the week, which would keep the cold air in place and potentially deliver frozen precipitation to much of the state.
Just for fun — keep in mind that this is not a forecast; just a bland description of what a model is showing, and these models run every six hours with frequent changes — this morning’s run of the GFS, a global model maintained by NOAA, showed several inches of accumulating snow for the Cumberland Plateau region with the potential mid-week system (and the midday run of the GFS that followed took that potential out of the equation entirely). Meanwhile, the ECMWF, a global model from Europe, doesn’t have the midweek storm system — at least not on the same scale as the GFS did — but it depicts minor snow accumulations over the Cumberland Plateau early in the week.
To be sure, accumulating snowfall is very unlikely next week. But much colder weather does seem to be a fairly safe bet.