textproduct: Columbia

WHAT HAS CHANGED

Confidence continues to gradually increase regarding the potential for an impactful winter event this weekend.

DISCUSSION

Key Message 1: Chilly temperatures expected tonight with lows into the upper teens to lower 20s.

Strong arctic high pressure centered over Kentucky this evening will bring mainly clear skies and light winds allowing temperatures to once again drop quickly tonight. Temperatures are expected to fall into the upper teens and lower 20s for most locations, colder in normally sheltered spots. At these temperatures, we begin to see cold weather impacts, so be sure to take precautions for people, pets, pipes, and plants. Temperatures will rise above freezing Wednesday morning.

Key Message 2: Guidance continues to trend towards a significant winter storm across the forecast area this weekend.

There continues to be signal a significant winter storm this weekend. Confidence is increasing in widespread, impactful snow/sleet/freezing rain accumulations across the forecast area, with a long duration winter storm possible.

From a synoptic standpoint, the signal for a significant winter storm this weekend is very robust. A strong, +3 standard deviations above normal surface high is forecast to invade the northern Plains and OH Valley on Friday, anchored by a strong upper-level jet stream and subsidence associated with convergence therein. As this occurs, a branch of the southern stream of the jet stream is forecast to amplify as a Baja Low deepens and slowly moves eastward. As the surface high pressure continues to shift eastward Saturday and Sunday, classic cold air damming is forecast to setup across the Carolinas and into Georgia, anchored by the upper level jet streak core to our north. The intensifying right entrance region of the then phased northern/southern stream jets is then forecast to shift east-northeastward, overspreading the southeastern CONUS with what 90-95th percentile integrated vapor transport values (IVT). This combination of an "atmospheric river" streaming atop the cold air damming is a unique, impressive setup for significant winter weather in this part of the country.

12z guidance is continuing the trend from the overnight guidance in strengthening the arctic high pressure system shifting into the northern Plains and Ohio Valley later this week, yielding a robust cold airmass across the forecast area this weekend. The upper level pattern remains fairly similar, with some slight delay in the ejection of the upper level trough across the southwestern US (guidance tends to eject these features a bit too fast in the longer range so this trend makes some sense). This is a trend seen amongst physics based models and their ensembles in addition to the AI guidance, increasing confidence in wintry precipitation. Additionally, with guidance continuing to show a robust and anomalous IVT signal, guidance has continued to trend a bit wetter than it was even 24 hours ago. As such, significant totals of snow/sleet/freezing rain are all possible at this stage. There is tremendous uncertainty regarding where all of these precipitation types set up and how much actually falls of each. Regardless of that, concern is increasing that this winter storm could be significant and impactful across the entire forecast area. The primary timeframe looks it could run from Saturday afternoon through Monday morning, with multiple rounds of heavy precipitation possible in this time span. Please continue to stay abreast of the latest forecast information over the coming days and begin to review your winter weather preparedness plan.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

VFR conditions expected through the TAF period.

High pressure is centered over the Mid-Atlantic into the southeastern states this evening. Satellite imagery showing only a few passing cirrus clouds although cirrus could become more scattered to broken on Wednesday. Light and variable to calm winds expected tonight before picking up from the southeast around 4 to 6 knots late morning after 16z and shifting more southerly late in the afternoon. Atmosphere remains well too dry to support fog concerns.

EXTENDED AVIATION OUTLOOK...VFR conditions likely continue into Thursday. The next storm system will likely bring restrictions as early as Friday, but more likely Saturday and Sunday.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.