“Snowmaggedon” or “Snow-Way”?! Looking ahead to next weekend (Dec 7-9)

When it comes to forecasting winter weather in the South, saying the word “snow” sets off quite the reaction to those who hear it — even if the chance of seeing a snowflake is little to none.

But the weather this weekend does warrant the use of the “s” word, especially as the calendar marches closer and closer to this “winter weather event”.

Timing is Everything

Example of “the wedge” over the Appalachian Mountains

As early as Thursday and Friday of last week, the GFS (or “American model”) was hinting at a winter weather set up over north Alabama, north Georgia, eastern Tennessee and the Carolinas. It was suggesting that a low pressure system would develop near the Gulf Coast, pulling warm and humid air into the region as cold, dry air was pooling into the Appalachian Mountains (known as “cold air damming” or more informally as “the wedge”).

This overall set up produces the classic “overrunning” event where rain falls into cold air, and if the cold air is able to extend high enough then snow would fall; if not, then the precipitation would either fall as sleet or freezing rain (rain that freezes on contact with a surface or the ground). However, the ECMWF (or “European Model”) was not convinced, and it called for a cold rain with highs in the 40s…

…But then, the models flipped!

Over this weekend, the GFS became more bullish that this coming Saturday and Sunday’s weather would fall as liquid rain, while the ECMWF started to align with the “older” GFS output in thinking that a wedge would set up, allowing a portion of the rain to fall as frozen precipitation — possibly snow, if not sleet and/or freezing rain.

And, it’s important to note that the timing of the onset of rain/frozen precipitation during warmer temperatures versus colder temperatures can “make or break” a forecast. IF warm air surges into our region and is stubborn to budge, then the rain will remain liquid. However, if the cold air arrives first, then we may see wintry weather.

It’s too early to buy all the milk, eggs and bread

Model data can only tell us so much so far in advance — this weather situation is still five days away! Until then, we need to see how robust “the wedge” becomes in the southern Appalachians, and if any of that cold “wedge” air is able to be wrapped into the Tennessee Valley.

Continue to monitor WHNT News 19 weather reports for the latest information, or check in with our forecast discussion as we get closer to next weekend.