Thunder and ice, deja vu

*** Update on December 23 -- the forecast below has worked out quite well, both in terms of the freezing rain and ice and in terms of elevated thunderstorms. Thunderstorms have followed the low-level jet up into southern IL, while the freezing rain has spread across IN into extreme west OH by evening. There continues to be a threat for a severe weather outbreak in the central US on Friday evening through Saturday. ***

Stu Ostro wrote a blog on December 18, showing a weather situation that evening that was conducive to a winter storm with freezing rain, sleet, and snow, and accompanied in places by thunder. Well, as I write this it's -- as they say -- deja vu all over again!

Places on Tuesday and Tuesday night December 23rd could again get freezing rain and sleet in east Oklahoma, Arkansas, Missouri, Illinois, and Indiana, and possibly western Kentucky and Tennessee. There is again a shallow layer of cold air 1000 to 3000 feet deep over this region. Warm, above-freezing, air is being lifted overtop of it. That makes for freezing rain and sleet. Precipitation either forms as rain in the warm layer or melts into rain from snow formed higher up. As the rain falls into the shallow cold layer near the ground, it chills and either freezes into little ice pellets (sleet) or on contact with the ground, trees, and other objects (freezing rain).

The map below shows one forecast of the surface map for 4PM Tuesday December 23rd. There is a low over southeast Colorado, with precipitation (violet) forming in the north-flowing air on its east flanks. (Maps courtesy of wright-weather.com)

Higher up, at 850 mb (about 5000 feet), the air is roaring northward at speeds in excess of 70 mph in places in Arkansas and Missouri (violet), as depicted below. This fast-flowing air aloft allows air at this level to warm quickly, while the slow-moving air near the surface stays cold.

I thought you might like to see a vertical slice of the atmosphere over northern Arkansas at this time, what we call a model-forecast sounding. The isotherms are in purple, slanted from lower left toward upper right. The freezing (0C) isotherm is labeled. The white line is the forecasted temperature profile (sounding). Where it is to the left of the 0C isotherm, it's below freezing (light blue shading). Where it's to the right of the 0C line, air is above freezing (red shading). Above 10,000 feet it is below freezing. This is a profile conducive to freezing rain.

Back on December 18th, the air near 5000 feet had temperature of 49F, while it was in the 20s at the surface. The model sounding suggests about 49F over 30F air in the upcoming event. That warm air aloft will also trigger isolated thunderstorms, forming upward from the 5000 foot level. They could give bursts of heavier sleet and freezing rain.

We're going into a pattern this week that looks more like November than December. There's even a chance of severe thunderstorms and a few tornadoes Friday and Friday night. Stay tuned to The Weather Channel to see how this forecast evolves.

Merry Christmas, Happy Holidays!