textproduct: Columbia

WHAT HAS CHANGED

The Winter Storm Warning is now in effect for the forecast area, running through 10am Sunday. Key Message 1 updated.

KEY MESSAGES

- 1) A potentially historic winter storm will impact the area.

- 2) A typically cold temperatures will accompany this snowstorm and bring several bitterly cold nights.

DISCUSSION

KEY MESSAGE #1: A potentially historic winter storm will impact the area.

Instead of rehashing the main synoptic features discussed in detail the last several days, we'll focus on the evolution of the mesoscale features and impact on the forecast/impacts.

Latest trends: Models have trended towards a slightly sharper upper trough with surface low pressure extending a little further south and west. Strong frontogenesis will develop in the NC Piedmont into the SC Upstate this morning and move into the Catawba, northern Midlands and possibly extend as far south as the central Midlands later this morning and afternoon. This should lead to enhanced snowfall rates for the northern half of the forecast area. Ultimately this has shifted the higher snowfall amounts slightly further south.

Impacts: We expect snowfall amounts from 6 to 9 inches from the central Midlands north to the NC/SC border. The heavier band of snow that should develop may bring even higher amounts locally. Elsewhere we are expecting amounts from 3 to 6 inches with the lower end of that range in the southern Midlands and south of Augusta, GA. However, there could be local enhancements in these areas too as the 500mb low moves overhead later this afternoon/evening. The most significant snowfall won't move into the area until mid to late morning. Travel conditions will quickly deteriorate through the day with winds gusting to around 30 mph at times during the afternoon and overnight. This may lead to blowing snow, further lowering visibilities and creating treacherous travel, especially in northern areas.

KEY MESSAGE #2: Atypically cold temperatures will accompany this snowstorm and bring several bitterly cold nights.

Tonight: Temperatures are expected to fall below freezing tonight with forecast lows generally in the 20s, with lower 30s possible in urban centers and in the southern CSRA. It is possible wind chill values approach Cold Weather Advisory criteria towards daybreak across our northeastern counties (Chesterfield, Kershaw, Lancaster, and Lee) and normally cold locations, but with an Extreme Cold Warning slated to go into effect tomorrow evening, opted to not issue a product for tonight with this package.

Saturday and Saturday Night: Likewise, while Cold Weather Advisory criteria may be met later today as the winds increase, the most severe cold will hold off until Saturday night. Temperatures during the daytime hours of Saturday will likely struggle to get above freezing, especially in the Midlands. No changes were made to the existing Extreme Cold Warning as criteria appear to be met around the start time of 7pm this evening. The abnormally cold temperatures will combine with increasing wind gusts of 25-35mph by Saturday evening to produce dangerously low wind chills of -5 to +5 degrees towards daybreak Sunday.

Sunday and Beyond: Temperatures do not recover significantly on Sunday following the snowstorm, meaning snow melt will be limited, especially across the Midlands. Any snow that does melt will refreeze Sunday night. Meanwhile, the existing snow pack will cause temperatures to drop quickly Sunday night. A Cold Weather Advisory will likely be needed for Sunday night for much of the Midlands, and perhaps the CSRA, but opted not to issue one with this package to avoid confusion with the existing Extreme Cold Warning. A warming trend is then expected to begin on Monday, putting an end to the cold weather threat for the forecast period.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Clouds Lower and Thicken Tonight Ahead of the Snowstorm....

Clouds are starting to lower across the terminals tonight as a winter storm begins to take shape. Have maintained a PROB30 group for snow developing towards daybreak, but a majority of the precipitation should hold off until later today. Periods of snow and increasing surface winds are expected as the day goes on, likely reducing visibility as well. Once conditions deteriorate, they will likely remain poor through the remainder of the TAF period.

EXTENDED AVIATION OUTLOOK...Restrictions should improve Sunday morning as the system departs. VFR conditions are then expected through at least the first half of next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Winter Storm Warning until 10 AM EST Sunday for SCZ016-018- 020>022-025>031-035-037-038-041-115-116-135>137. Extreme Cold Warning from 7 PM this evening to 10 AM EST Sunday for SCZ016-018-020>022-025>031-035-037-038-041-115- 116-135>137. GA...Winter Storm Warning until 10 AM EST Sunday for GAZ040-063>065- 077. Extreme Cold Warning from 7 PM this evening to 10 AM EST Sunday for GAZ040-063>065-077.