textproduct: Columbia

WHAT HAS CHANGED

Winter Storm Warning issued for the forecast area which will go into effect from 10 PM this evening to 10 AM Sunday.

Aviation discussion for the 12z TAF issuance.

KEY MESSAGES

- 1) Significant snow storm expected this weekend.

- 2) Well-below normal temperatures likely continue into early next week. An Extreme Cold Watch remains in effect Saturday night into Sunday morning.

DISCUSSION

KEY MESSAGE #1: Significant snow storm expected this weekend.

Summary: The Winter Storm Watch has been upgraded to a Winter Storm Warning as confidence builds in significant snowfall. Snow amounts are expected to be highest in the northern Midlands and near the NC/SC border with total snowfall forecast to be between 6 to 8 inches. Across the remainder of the area 3 to 6 inches is generally expected but could vary locally. Wind gusts above 30 mph will be possible which could lead to blowing snow and reduced visibilities as well as very cold wind chills (mentioned more in key message 2).

Forecast Confidence: An abnormally deep upper level trough will swing through the Southeast on Saturday and Sunday. The depth of the trough will be near the climatological maxima with a rapid intensification of a coastal low to our south and east. This is a favorable climatological setup for our most notable historical snowfall events with cold air in place and upper troughing over the eastern US, reinforced by the much colder air mass to the west moving into the area. Although confidence in snowfall over the area in general is higher than a typical winter event, there are still some small scale features which could lead to varying amounts in localized areas. Mesoscale processes such as banding and dynamically induced snow showers as the upper low moves overhead could lead to locally higher amounts. Forecast snow to liquid ratios are also far above normal for this region of the country. This could lead to phenomena rarely seen in the region such as blowing snow.

Timing: On Friday evening there is some potential for precipitation as weak moisture advection develops. Forecast soundings show that the snow growth region may not be saturated until early Saturday morning for most of the FA. This could allow for some rain 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 overnight as cold air continues to move over the region. Snow rates should pick up through the day as the upper trough approaches continuing into the evening. Snow is expected to move out of the area by Sunday morning.

Impacts: Significant snowfall amounts, strong winds, and bitter cold may lead to dangerous travel conditions on Saturday and Sunday. With temperatures near or below freezing through the day on Sunday we may see travel impacts extend into early next week. There is potential for this system to produce the highest snowfall totals over the area since the February 2010 snow storm and fall into the top 20 of snowfall events for the Columbia and Augusta areas.

KEY MESSAGE #2: Well-below normal temperatures likely continue into early next week. An Extreme Cold Watch remains in effect Saturday night into Sunday morning.

Broad upper troughing remains entrenched over the area ahead of the incoming winter weather. This is expected to keep temperatures below average, although today is forecast to be warmer than the past few days (and the next few days). With the onset of winter precipitation expected tonight, temps are expected to be cold once again, but likely above Cold Weather Advisory criteria. As the snow continues on Saturday, temps don't rise that much and most of the forecast area stays below freezing for the entire day. The main exceptions being in the CSRA and southern Midlands, where temps could edge above freezing by a degree or two. A shot of reinforcing cold air arrives Saturday night into Sunday morning as the system begins to exit the area. In addition to likely record setting cold ambient temps, the winds mentioned in Key Message #1 will cause wind chill values to drop to near 0F for much of the forecast area. Thus, an Extreme Cold Watch remains in effect. It should be noted that at these wind chills, frostbite can occur in the matter of 30-40 minutes to exposed skin. Frigid air hangs on for Sunday night, thanks in large part to the expected fresh snow pack. Lows Sunday night could reasonably be colder than Saturday night, but wind chills will likely be higher than Saturday night due to light winds caused by high pressure. Nonetheless, a Cold Weather Advisory is looking more likely for Sunday night.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

VFR conditions to begin the TAF period with ceilings gradually lowering to likely MVFR, potentially IFR, at the end of the period.

High clouds are streaming over the region at the time of this writing. Expect these clouds to increase in coverage as ceilings gradually lower through the TAF period. Ceilings are likely to be in the MVFR category late in the period, with IFR cigs possible. Light east winds around 5 kts are anticipated to persist into the afternoon, followed by a shift to more southeasterly winds. Winds expected to switch again to northeast as they begin to increase to 5-10 kts after about 00z. A few higher gusts are possible at the end of the period, but confidence is too low at this time. An approaching system is expected to bring snow to the terminals late tonight into Saturday. However, latest hi-res guidance pushes the onset back somewhat and likely affect the terminals after this TAF period.

EXTENDED AVIATION OUTLOOK...Impactful aviation weather becomes more likely Saturday as a low pressure system moves into the region with wintry precipitation likely.

CAE WATCHES/WARNINGS/ADVISORIES

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