North Atlantic Oscillation forecast for the next two weeks
Climate Forecast System forecast for February 6th - 11th
Climate Forecast System forecast for February 13th - 18th
GFS forecast for Tuesday February 19th
The transition from late January into early February in Middle Tennessee saw severe weather yield to rounds of snowfall. Climatologically speaking, February is the snowiest month of the year around Nashville. That doesn't appear to be the case anytime soon; as we move through this week, expect temperatures to remain a bit above average in the 50s and possibly lower 60s.
One thing meteorologists monitor to determine long-range weather is the North Atlantic Oscillation. When the NAO is positive the jet stream follows a brisk west-to-east pattern across northern North America, which prevents prolonged cold snaps in the eastern United States. Right now the NAO is forecast to remain positive through the upcoming weekend (see first image). My seven day forecast reflects that, with highs in the 50s and 60s during that time frame. The Climate Forecast System long-range model backs me up. You can see a large area of above-average temperatures between the 6th and 11th of February (see second image).
A negative NAO represents a more sinuous jet stream from North America into the North Atlantic, which can allow a ridge of high pressure to develop over Greenland. When that occurs, the cold air is prevented from moving east and is shunted south into the eastern half of the United States. The GFS ensemble shows that the NAO value could turn negative early next week, around February 12th (check out the first image). The Climate Forecast System coincides with the NAO flip and shows a return to colder-than-average conditions from the middle of next week onward (noted in the third image).
While predicting whether temperatures will be above or below average is feasible over the course of a couple of weeks, it is much more difficult to predict if a specific weather system will interact with the cold air to give us any snow chances. I wanted to show you the GFS model's predicted upper air pattern for the middle of the month (fourth image). It shows a piece of the polar vortex in south-central Canada on Tuesday, February 19th. That would mean some very cold air for the Upper Midwest and a southwest-to-northeast-oriented flow across the Mid-South. If we have enough cold air in place, we may be able to squeeze out one or two snow threats during the middle of the month. Right now, however, I don't see any major snowstorms in the works for Middle Tennessee over the next two weeks.
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