Warming up early in the week, but Arctic air mounts a comeback!


The wintry mix changed to mostly snow within a few miles of the Alabama-Tennessee state line Saturday night and in some of the elevated areas in Northeast Alabama (including Monte Sano, parts of Sand Mountain and the Cumberland Plateau. Lewisburg, Tennessee got two inches, but areas near Cookeville, Tennessee got over SIX inches of snow by daybreak Sunday.

Huntsville? We’re still missing out. It’s been now 2,174 days since an inch of snow or more fell in the city.

Does it look like we’ll break that streak this season?

Not right now.

The odds of total snowfall through February 23rd (based on long range ensemble guidance) is less than 30%:

Probability of snowfall exceeding 1″ through 6 AM, Feb. 23, 2021

Arctic front: small moves and big changes

If you’ve followed the forecast over the past seven days, you’ll remember that it was supposed to be really cold for Super Bowl Sunday and Monday: highs in the 20s, lows in the single digits. That was a huge miss because of the position of an Arctic cold front.

Arctic fronts have very sharp changes from one side to the other: sometimes 50 degrees over a space of few hundred miles. That seems like a long distance if you’re driving, but for the atmosphere…it’s not that far! For computer models that try to ‘model’ the entire atmosphere, it’s a little too hard to resolve. That’s what accounts for the wild swings in the forecast lately: small geographical moves mean big changes to the weather at YOUR house.

Surface map and surface temperatures showing the approximate location of the Arctic boundary at 2 PM Sunday. Less than 500 miles separates mid-10s in St. Louis to low-50s in Atlanta.

So what will we do with this boundary?

The early goings of the forecast are pretty clear: it retreats to the north, so we don’t have to worry about it on Monday, Tuesday or Wednesday.

On Thursday, an area of low pressure develops along it, and that low will force it south again for Friday and the weekend.

As of now, we are discounting the extreme cold potential for North Alabama and Southern Middle Tennessee. The American-run GFS guidance shows lows in the single digits next weekend; no other guidance even comes close to that.

This? It might be possible, but it’s not a reasonable solution for real-world, Alabama weather around Valentine’s Day given the pattern at hand.

For now, we’re confident in the warm-up through midweek. Confidence is high in rain by Thursday with that next low along the Arctic boundary. Confidence is low in the extent of the cold air able to move this far south.

Here’s more guidance called the NBM: National Blend of Models. It has some human control, but it’s mostly an average of the computer models we have available. It actually works pretty well: better than most individual models we have available.

It gives us a view toward how many different possibilities there are for the weather on a given day. Some we can easily discount. Some are plausible but not realistic, and some are what we’d expect to be a reasonable scenario. The ‘reasonable scenario’ is what you see on our Seven Day Forecast.

The upper-air pattern is not supportive of record-breaking cold this far south; however, it would be reasonable to expect temperatures up to 15°F below average by next weekend.

What’s average? Huntsville’s ‘average’ high on Valentine’s Day is around 55°F; the average low is around 35°F. That’s why we have temperatures in the 40s for highs and 20s for lows on our Seven Day Forecast. You might see different numbers on an app, but that’s the ‘most likely’ solution given the information we have.

Oh, and there’s still no real threat of snow or ice out there that is a reasonable scenario given the current weather pattern. Is it possible? Sure. Is it likely? Not exactly.

Looking for the rest of the forecast? It’s always online at WHNT.com/Weather and in the “Daily Forecast” section on Live Alert 19!

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