Wintry precipitation chances increasing for parts of the South and Southeast

Wintry precipitation chances increasing for parts of the South & Southeast. Numerical guidance continues to advance the Arctic cold front farther south & east faster than previous runs. The latest trends suggest a faster movement of an airmass that may be conducive for wintry precipitation as well as indications that the airmass will be one or two degrees cooler than initially thought. This is no surprise given how models struggle with these dense, shallow cold airmasses. This is increasing the opportunity for a brief window to see rain change to a rain/snow mix, possibly a complete changeover to all snow, late Tuesday into early Wednesday for parts of the region.

As the cold front moves through the mid-South Tuesday, followed by a passage overnight Tuesday into early Wednesday for the Southeast, impressive isentropic lift will occur in the post-frontal airmass due to a vigorous piece of energy to the southwest in the upper-levels of the atmosphere. At the same time, a nice feed of Pacific moisture will stream into the mid & upper-levels of the atmosphere. This will lead to a large shield of precipitation developing. Initially, based on forecast soundings, some of the precipitation may evaporate before reaching the ground as cold/dry air filters in at the surface behind the cold front (this evaporation process would act to allow temperatures at the surface to decrease a couple degrees). Once the lower levels of the atmosphere moistens, a cold rain would begin.

The big question is how long will the precipitation occur in the post-frontal airmass. Climatologically, 8 times out of 10, the moisture gets scoured out before the atmosphere becomes cold enough to support wintry precipitation; however, with the latest trends of the faster cold front arrival, the airmass being a couple degrees colder, and the Pacific moisture at the mid & upper-levels of the atmosphere (seeder-feeder), models are biting onto & converging on a solution that shows a rain/snow mixture will occur for central Arkansas, Tennessee, northern Mississippi, northern Alabama, northern Georgia and western North Carolina.

Figure 1: Future radar Tuesday evening
Figure 2: Future radar Tuesday night
Figure 3: Future radar Wednesday morning

Right now, no major accumulations are expected; however, if a transition to all snow occurs for a couple of hours, light accumulations would be possible–especially on elevated surfaces. The best chance for accumulations will occur in Tennessee where 1-2″ may fall. This forecast is extremely fluid and needs to monitored over the next 24-48 hours for possibly significant changes to the forecast.