textproduct: Columbia

WHAT HAS CHANGED

Winter Storm Watch issued for the forecast area from Friday evening through Sunday afternoon.

KEY MESSAGES

- 1) Snow expected to cause hazardous travel this weekend.

- 2) Well-below normal temperatures will continue through early next week, with frigid air expected Sunday morning.

DISCUSSION

KEY MESSAGE #1: Snow expected to cause hazardous travel this weekend.

Summary: A Winter Storm Watch has been issued for central SC and east-central GA from Friday evening through Sunday afternoon. A highly anomalous cold air mass will settle into the region over the weekend. As a coastal low develops, moisture will be pulled into the Southeast and Mid-Atlantic setting up favorable conditions for impacts from snowfall from the area. The northern Midlands are most likely to see significant snowfall with amounts from 3 to 6 inches possible. Although the southern extent of snowfall is less certain, chances are increasing that the remainder of the forecast area could receive accumulations of 1 to 3 inches.

Forecast Confidence: On Saturday, an abnormally deep 500 mb low will move near or over the forecast area as a coastal low develops to our south and east. The NAEFS ensemble forecast for the strength of the 500 mb low falls near the edge our outside of the 30 year climatology for this time of year. The extreme cold pool aloft brings some challenges to the forecast including mesoscale processes which may not be reflected well in global models but also forecast snow to liquid ratios far above normal for this region of the country.

Timing: Ahead of the 500mb low, we may see shallow moisture advection into the area on Friday evening and early Saturday morning as low pressure begins to develop to our south. Forecast soundings show that the snow growth region may not be saturated until later Saturday morning for most of the FA. This could allow for some drizzle/sprinkles until colder air moves in aloft and ice is introduced to the cloud. Although there may be a brief mix of rain and snow we would expect a quick transition to all snow as cold air continues to move over the region. Depending on the track of the system we could see snow continue into Saturday night, especially as the cold pool aloft moves overhead. All precip is expected to lift away from the area Sunday morning with bitterly cold winds in the wake.

Impacts: What is expected to be a dry snow would lead to hazardous travel over the weekend with the greatest impacts expected in the northern Midlands. Bitterly cold temperatures and wind chills could extend travel issues into Monday with only a short window, if any, of temperatures above freezing on Sunday.

KEY MESSAGE #2: Well-below normal temperatures will continue through early next week, with frigid air expected Sunday morning.

Deep and broad mid and upper level troughing continuing through the weekend and into early next week keeps temperatures below normal for much of the eastern CONUS including the SC Midlands and CSRA. Highs Thursday are forecast to be in the 40s, with temps topping out around 50 for much of the area while lows remain in the 20s through Saturday morning. Reinforcing cold air is expected to move in with the weekend winter system discussed in Key Message #1, keeping highs generally below freezing on Saturday. The bigger concern is Saturday night/Sunday morning. With the expected fresh snow cover, temperatures are forecast to drop into the low to mid teens. In fact, the NBM shows a high chance (70-80%) of lows less than 15 degrees across the forecast area, which would break the record lows for both CAE (16F) and AGS (17F). The latest run of the NBM, has 50th percentile low temps for Sunday morning at 12F for both CAE and AGS. In addition to these frigid temps, winds are forecast to gust to 20-30 mph, with a low chance (10-20%) of gusts greater than 30 mph. The temps combined with these winds would result in bitterly cold wind chills, between 0-5F, which would meet the criteria for an Extreme Cold Warning. As such, an Extreme Cold Watch may need to be issued later today or tonight assuming these trends continue. While we still don't expect to be near any cold weather headline criteria until this coming weekend, the persistent cold weather could present a compounding problem with poorly insulated pipes and anyone without access to sufficient heating.

AVIATION /06Z THURSDAY THROUGH MONDAY/

VFR conditions expected through the TAF period.

High pressure is expected to drift over the area through the TAF period. As a result, the elevated westerly winds currently being observed are forecast to become light and variable to calm. Winds remain light and variable through the remainder of the TAF period after that. Clear skies give way to some cirrus clouds later this morning.

EXTENDED AVIATION OUTLOOK... VFR conditions likely through early Friday. After that, impactful aviation weather becomes more likely into the weekend as a low pressure system likely moves somewhere near the region and brings the possibility of wintry precipitation.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Watch from Friday evening through Sunday afternoon for SCZ016-018-020>022-025>031-035-037-038-041- 115-116-135>137. GA...Winter Storm Watch from Friday evening through Sunday afternoon for GAZ040-063>065-077.