textproduct: Columbia

WHAT HAS CHANGED

Key Message and Aviation Update

KEY MESSAGES

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

- 2) Atypically 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 deeper and more negatively tilted 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 will bring even higher amounts locally. The HREF LPMM and PMM indicates some isolated spots potentially up to 12 inches in this heavier band across the northern Midlands counties, nearer the NC border. 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.

Today and Tonight: Temperatures fell steadily through the night and currently range from the upper 20s to lower 30s in the Midlands and the lower to mid 30s in the CSRA. Temperatures during the daytime hours will likely struggle to warm today, especially across the Midlands. Wind chills are expected to decrease as the day goes on due to falling temperatures and increasing winds, with an Extreme Cold Warning going into effect at 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 /12Z SATURDAY THROUGH WEDNESDAY/

Conditions Continue to Deteriorate this Morning....

Ceilings at the terminals at daybreak have fallen into the MVFR category as snow showers have started to develop. Periods of snow, IFR ceilings, and increasing surface winds are expected as the day goes on. The snow and winds will likely reduce visibility as well. Once conditions deteriorate, they will likely remain poor through much of the TAF period, gradually improving during the overnight hours, with snow coming to an end towards the end of the period.

EXTENDED AVIATION OUTLOOK...Conditions continue to 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.