Monday, November 28, 2011

December 4-9 Potentially Major Snow Event

12z GEM Forecast Tracks
(December 4-9 Storm is Track coming out of Texas/Oklahoma)

12z NOGAPS Forecast Tracks
(December 4-9 Storm is Track coming out of Texas)

18z GFS Forecast Snow Depth
12z ECMWF Snowfall
Various Models are indicating the potential for a snowstorm in the December 4-9 timeframe. This system would come as a low pressure system cut off from the jet stream that would hang around the Southwest for a day or two. After that, this system would supposedly move to the general NE/NNE (depending on model discretion) and affect the Midwest.
The models are very spread about right now, and they ought to be- it's winter transition time, which is never easy for the weather models. We do have some disorganized 'camps' set up: the north track or the south track The north track involves the ECMWF solution shown above, while the south track is more like the NOGAPS track. Here's the gist of the models right now:

North Track: ECMWF, GEM, DGEX, JMA
South Track: GFS, NOGAPS

(Note: JMA and DGEX are not very reliable models)
This will likely come down to the eleventh hour, so to speak, so let's check in on the ensembles, which are much more reliable and consistent than the models themselves at this point. Using the same definitions for the north and south tracks, here's the ensembles take.

North Track: ECMWF Ensembles
South Track: GEM Ensembles, GFS Ensembles

We are not going to even try to call this one, as the models swerve like a car going down a very icy road.

Concern For Heavy Snow In Tennessee

There is potential for snowfall rates of up to 1 inch an hour as a cold-core upper level low circles in Kentucky/Tennessee. A cold-core upper level low (ULL) system is basically a low pressure system with cold air in the center of it. That's how snow is possible in Tennessee into Mississippi, Alabama. It is not out of the question that accumulating snows may fall in the aforementioned areas. As this cold core ULL eventually moves off, our concern will shift to another threat that may involve a snow threat for Wisconsin later on in the week.