Sunday, January 26, 2014

January 28-30 Potentially Historic Southeast Snowstorm

Things appear to be setting up for a potentially historic snowstorm in the Southeast over the January 28-30 period.

The NAM model is the most aggressive with this storm system, dropping as much as 18.1" inches on the Southeast. As the legend on the right shows, we would be seeing accumulations over 6 inches in far southern Mississippi, and snow amounts over 1 foot slamming southern Alabama, much of Georgia, much of South Carolina, and eastern North Carolina. There is also 12"+ being forecasted in the panhandle of Florida, near Pensacola. Now, the NAM is notorious for over-doing snowfall, and I've got a feeling this situation applies here. If the storm does end up happening, you could probably cut these totals in half or so and end up with what we will see. Regardless, you get the picture: considering any snowfall in the South is a big deal, this much accumulating snow could be not only historic, but disastrous for those not used to snow falling in states like Georgia or Alabama.

The GFS model shows its forecast for all four types of precipitation for this event: ice pellets (top left), freezing rain (top right), rain (bottom left), and snow on the bottom right. The snow panel shows liquid equivalent snow amounts, meaning 0.5" on that bottom right panel would typically equate to 5" of snow. We see the GFS puts down all types of precipitation for this event, with freezing rain and ice pellets targeting southern Louisiana, southern MS/AL, central Georgia and eastern South Carolina. The snowfall hits areas immediately north of those two precipitation types. It looks like the GFS wants to lay down nearly 10" of snow in the Carolinas, though I'd put that at closer to 8 or 9 inches, considering the snow should be more or less heavier than your standard 10:1 ratio snow, where 10 inches of snow equals 1 inch of water. The GFS, while lighter in snow amounts than the NAM, still shows a pretty intense snow event for the South, with all forms of precipitation hitting the southern states.

The final model to look at here is the ECMWF model, which shows a much less significant snow event. We see the heaviest snow hits the coastal regions of South and North Carolina, where 6"+ of snow would be expected. The states of Georgia, Florida, Mississippi, Alabama, Louisiana and even Texas receive only a couple of inches of snow in this scenario. Based on the ECMWF Ensembles, I think the model is a little light on snow amounts across the board, and the more conservative estimates would probably range around the 2-5" range for the states previously mentioned.

This does look like a significant, and possibly historic snowstorm for the Southeast. My thoughts on the system side with the GFS model right now, which shows snow amounts decently as shown below. It would be wise to take off a couple inches here and there, specifically in the hardest hit areas, just to account for likely mixing of precipitation during the event.


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