It just got interesting
POSTED 2:27 PM, FEBRUARY 12, 2015,
We've known for a while now that there could be a “threat” of some wintry weather early next week, but confidence is increasing that a major winter storm could unfold across the South between Monday and Wednesday.
All of the players are on the field, but their positions matter a lot. A surface high over the northeastern US and a low near the Gulf Coast often signal big snows for this area; however, the uncertainty of the exact track of the low casts a big shadow over any pinpointed expectations. If it’s farther north, we get more rain than anything in the Tennessee Valley. It would be areas nearer Interstate 40 that get a big blast of wintry weather. If it’s farther south, the greater threat could be suppressed closer to Interstate 20. There’s a lot of miles between those two major highways, but our longer-range forecast models see that kind of distance as very, very small (margin-of-error kind of stuff).
In fact, if you look at individual members of an ensemble, the positions of the main players may change by hundreds of miles – and that’s within the same “model world!” These three maps are the ensemble means; you could look at it as the average position of all the members of the GEFS ensemble product. That looks awfully wintry for us if it pans out:
PHOTO GALLERY
Some guidance puts as much as 12 inches of snow over Southern Tennessee by Wednesday morning. An event like that is so rare that it is hard to “forecast.” Forecasts are “best estimates” of the many potential outcomes, and big, record-setting events don’t happen often.
12Z (6 AM) GFS model-derived snowfall at a 10:1 ratio
Things to Watch: We’ll keep close tabs on the trends in the model guidance. If it trends 100 miles north or south, it could greatly change what happens at your house.
If it does pan out, watch the snow accumulation ratio (how much snowfall for an inch of liquid precipitation). It would probably start out around 8:1 (8 inches of snow for every one inch of liquid) and end up around 20:1 when the fresh Arctic air catches the moisture. That could throw totals way off if you just base it on the simple, common 10:1 ratio.
Forecasts like this are never simple, and they change often. Stick with us and we’ll keep a close watch on it for you.
What Do I Really Think? It’s going to be a complicated mess. That’s what I think right now. The scenario we see as of now starts out as some ice and snow on Monday, likely changes to rain for most of North Alabama (stays icy in most of Middle Tennessee) Monday night into Tuesday, then it changes back to some sleet and snow Tuesday night and Wednesday morning. The back-and-forth of the precipitation types make it impossible to “nail” an accumulation amount, but it is not far-fetched at all to expect at least 1-3″ of snow by Wednesday. That could change in a big way (to go higher or go to nothing), but it’s a reasonable expectation given what we know today. Some travel problems are possible, but there is no way to gauge timing and impact yet.
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