December 20 - 10:15 AM
WINTER STORM LIKELY IN NORTH-CENTRAL U.S. THIS WEEKEND, BUT A LOT OF UNCERTAINTY THIS FAR OUT.
What is this graphic, you ask?
...It’s a 500 mb vorticity forecast for Wednesday morning, which is a measure of spin of air parcels. In this case, it’s close to 3 miles above the earth’s surface. The circled area is a vorticity maxima, which in part will form our weekend storm system. By Wednesday morning, this will be roughly a THOUSAND miles west of Alaska! The upper-level energy won’t even reach the West Coast until early Christmas Eve.
Nothing could go wrong with snow forecasting, right?!
A trough in the jet stream is going to dig across the western states late this week, which in turn, will form a strong surface low that developed from upper-level energy which originated west of Alaska. Wow, that’s a lot!
Meteorologists interpret messy-looking graphics like this. Computer models have advanced and improved exponentially the past several years. But when we’re looking at something in the atmosphere several thousand miles away, we can only forecast a trend, not specifics. As the weekend gets closer, the specifics get narrowed down.
The trend calls for a winter storm, especially Christmas Day into Monday. Computer models have been consistent the past two days seeing this trend. The rest is just a guess this many days out. Some models are forecasting a major storm with over a foot of snow. Is that possible? Yes. Is it reliable to broadcast snowfall forecasts? To me, absolutely not. Even if the models get it right, it was still just a best guess given the latest data this many days out. If you roll the dice, sometimes your predicted number is rolled. Sometimes not. To say the potential is there would be accurate. The key is “potential”.
Meteorologist Kevin Lawrence