Monday, January 27, 2014

January 28-30 Historic Southeast Snowstorm - Updated 10 AM (ET) 1/27

This is an updated model analysis to the earlier posts concerning the January 28-30 Potentially Historic Southeast Snowstorm.

We begin with the NAM model, which really toned down snowfall amounts for the area as a whole. As I had previously discussed, there was skepticism towards the 21" amounts the NAM was previously showing, so this decrease in snowfall amounts was anticipated. We now see a band of spotty 6" totals extending from southern Louisiana and Mississippi into a band of 6-9" across southern Alabama and Georgia before amounts begin to flirt with the 12-inch mark in the Carolinas. I'm still a little skeptical of the higher amounts in the Carolinas, as this event will be a low-ratio event. This means that instead of snow being the usual 10:1 quality type, meaning 10 inches of snow could be melted down into 1 inch of water, this snow should be closer in the ballpark of 8:1 or 9:1, meaning 8 inches of snow could be melted down into 1 inch of water. This means higher water content in the snow, and this is due to the likely mixing of precipitation in areas that do get snow, where switching between periods of snow, freezing rain and sleet is to be expected. This low-ratio snow will be heavier than normal due to the higher water content, so any shoveling done in the wake of this storm must be done with utmost caution.

The ECMWF model is much lighter than the NAM model, which is to be expected thanks to the NAM being notorious for putting out too much snow in its forecasts. However, I'm skeptical of these low amounts forecasted by the ECMWF. We see a general 1-3" swath from east Texas into southern Georgia, and only in southern Georgia do we ramp up amounts into the 3-6" range. The far eastern Carolinas then encounter amounts closer to 8-10". I feel that the amounts in Georgia should be beefed up a bit, and the overall snow swath nudged a bit to the north and west so the snow is more onshore than offshore. I could also see some snowier forecasts than what we see here in southern Mississippi and Alabama, but that's a little more iffy than the other areas.

We then take a look at the GFS model, which is closer to what I think will actually happen. We see a swath of 1-3" across eastern Texas before 6-10" totals pop up in southern Mississippi and southern Alabama. I feel that the totals in these areas will probably be revised downwards in future forecasts. We then see a band of 3-6" across Georgia, which ought to be a bit more to the south, and then we see an expanse of 10-13" in the Carolinas. Out of the three model solutions we've reviewed thus far, I'm thinking the GFS idea for the Carolinas has the best shot at verifying. We see the heaviest snows more onshore than offshore, and the heaviest amounts are in the 10-13" range, not the 20-25" range. There will probably be adjustments made for snow totals in areas to the west, but the GFS looks to be handling the Carolinas decently in my opinion right now.

I still stand with my forecast, keeping heavier amounts more onshore in the Carolinas than not, and kicking off the whole event with 1-3" in southern Texas and southern Louisiana, transitioning to a 4-8" event in southern Mississippi and southern Alabama. I'm not really seeing the highest amounts get past 13" right now, though I suppose the potential is theoretically there, as forecasting models have had the trend this winter of underforecasting snow totals. In this case, however, we should see amounts closer to 8-10" in that pink swath in my forecast above, with the 12"+ demarcation reserved for very isolated 12"+ totals.

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