Meet the new snowpack, same as the old snowpack
We're now under a Winter Storm Warning as the official forecast for Cape Girardeau calls for 6-8 inches of accumulation Wednesday into Wednesday night.
The computer models have been struggling with this system -- just as they seem to struggle with every winter storm. The biggest hiccup is the possibility that a layer of warm air aloft could yield sleet instead of snow for a portion of the day Wednesday, which would reduce total accumulation amounts.
The NAM computer model has tended to be the most bullish on snowfall amounts, although it has backed off slightly in the latest version. It shows Cape Girardeau County at the edge of the heaviest amounts, ranging from 5 to 10 inches from northwest to southeast across the county. It paints 16 inches for a small corridor to our east:
Meanwhile, the GFS model has been more conservative, but it is starting to creep upward with its totals. This version shows 6-8 inches across Cape County:
Amounts are much lower to the north and south, which means this storm would only need to wobble slightly to drastically change the outcome.
Guidance from the Weather Prediction Center -- which looks at the consensus of many computer model runs -- shows very high snow probabilities. Cape has a 90% chance of receiving at least 2 inches of snow, an 80% chance of getting at least 4 inches, a 40% chance of seeing more than 8 inches, and, yes, even a 5% chance of winning a whole foot of snow.
Here's the map showing the probabilities for 8+ inches:
Looking closely at the forecast charts, we should slip below freezing some time between 3 AM and 6 AM tomorrow morning. That will allow rain to change to freezing rain before transitioning to sleet, then a sleet/snow mix, and finally all snow. The Winter Storm Warning officially runs from 6 AM Wednesday through 6 AM Thursday.
I should point out that there is always a bust potential with these storms. Remember that the forecast for today had been calling for rain and temperatures near 50F -- so far we've only had fog and temperatures barely above 40. So if the models were off today, they can be off tomorrow.
The new snowpack should help temperatures plummet yet again, with a low of +3°F expected Thursday night. We will rise above freezing on Saturday to start a long thaw. So while this new snowpack won't last as long as the old one, it's still going to be a mess for a few days.
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