textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Snowfall totals have increased for the high elevations of the NC mountains Friday night and early Saturday.

Confidence remains low for snow east of the mountains Saturday night/Sunday morning, though precip/snow chances have crept upward across the area.

Very cold temperatures and mountain wind chills Monday night and Tuesday.

KEY MESSAGES

1. Frigid Arctic air will linger over the Carolinas into Friday. The combination of cold temperatures and gusty winds will produce very cold wind chills, especially at higher elevations. 2. Fire weather threat today and again on Friday. Low relative humidity values combined with gusty winds have produced favorable conditions for wildfires to spread. However, the cold temperatures should limit the overall threat. 3. Light snow accumulations over the North Carolina mountains and possibly the mountains of northeast Georgia and the Upstate Friday night through early Saturday could result in minor travel issues, mainly at high elevations. 4. We continue to monitor the evolution of model guidance for Saturday night and Sunday with some interest, given the consistent GFS depiction of snow potential, but a lack of consistency between models keeps confidence low. 5. Another cold air mass will settle over the region through the middle next week. A Cold Weather Advisory might be needed for parts of the mountains Monday night into Tuesday.

DISCUSSION

Key message 1: Frigid Arctic air will linger over the Carolinas into Friday. The combination of cold temperatures and gusty winds will produce very cold wind chills, especially at higher elevations.

With the strong Arctic cold front well to our east, sfc high pressure is spreading over our area from the west. We are ob- serving mostly clear conditions on satellite, with the excep- tion of bkn to sct stratocu over the NC mtns. Light, NW flow snow flurries will likely continue over the favored west-facing slopes along the NC/TN border thru the afternoon, before taper- ing off entirely by sunset. With the bulk of the snowfall now done, the Winter Weather Advisory was allowed to expire at noon. Winds will remain gusty thru the afternoon, with gusts tapering off this evening outside of the mtns. Over the NC mtns, they will likely remain gusty into late tonight, especially over the northern NC mtns. As a result, there could be isolated visibility issues in the mtns, where blowing snow kicked up by wind gusts creates problems. Additionally, very cold wind chills, as low as 10 degrees below zero, are expected across the higher elevations again tonight. As such, a Wind Advisory remains in place through 7 PM this evening, and a Cold Weather Advisory remains in place through 7 AM Friday morning for ele- vations above 3500 feet.

Key message 2: Low relative humidity values combined with gusty winds have produced favorable conditions for wildfires to spread. However, the cold temperatures should limit the overall threat.

Gusty winds will continue thru the afternoon and into the evening. So far this afternoon, we've seen dewpts mix out a decent amount across our fcst area. Current observations are showing most sites reporting RH values in the 20 to 35% range, with the potential for lower values over the next few hrs. Consequently, fine fuel moisture will likely drop to critical levels. The main limiting factor will likely be temperatures, with highs struggling to reach 40 degrees today across the lower elevations. As such, a Fire Danger Statement is in effect for all of our Upstate South Carolina, NE Georgia, and Piedmont North Carolina zones until 7 PM. In addition, conditions look favorable again Friday afternoon for increased fire danger, and another Fire Danger Statement may be needed for Friday. If you burn, use extreme caution!

Key message 3: Light snow accumulations over the North Carolina mountains and possibly the mountains of northeast Georgia and the Upstate Friday night through early Saturday could result in minor travel issues, mainly at high elevations.

A fast-moving short wave will rotate around the bottom of a digging upper trof over the Plains/Midwest Friday night then shear out as the wave moves north of the area on Saturday. It will be strong enough to push a cold front across the area Saturday. There is also just enough mid-level DPVA, just enough weak upper divergence from a jet streak developing over the mtns, just enough isentropic lift on the east side of the jet axis, just enough WSW upslope flow at low levels, and just enough moisture return from the western Gulf ahead of the wave to support precip developing and moving east over the mtns Friday night and Saturday morning. Thicknesses/temps continue to show an elevation dependent rain/snow scenario. The forcing lifts past to the northeast fairly quickly while not translating much east of the mtns such that precip should be lifting out and drying up by mid-morning Saturday. That said, precip chances will be fairly high across the western Upstate and NE GA. In those locations, snow may mix with rain at the highest elevations but not significant accumulations are expected. There could even be some sleet mixing in at any location where precip develops as the temps wet bulb down in evaporational cooling. Again, any sleet would be short lived with no significant accums. The better chance for accumulating snow will be the higher elevations of the NC mountains. QPF remains the question as the latest guidance has trended toward higher amounts in the upslope areas of the Smokies and Balsams. This translates to some significant snowfall there. That said, county wide averages would limit any Advisories to the higher elevations. Given the uncertainty and timing of precip onset, will hold off on any products for now.

Key message 4: We continue to monitor the evolution of model guidance for Saturday night and Sunday with some interest, given the consistent GFS depiction of snow potential, but a lack of consistency between models keeps confidence low.

Another short wave diving into the central CONUS will deepen the upper trough to our west Saturday night. The short wave and trof axis cross the area on Sunday. This creates cyclogenesis off the Carolina coast along the frontal boundary from Saturday. Southerly flow develops Saturday night with increasing moisture and isentropic lift across the area. Deep layer forcing and frontogenesis takes place as well. All of the guidance pretty much agrees on this, although with some differences where the axis of heaviest precip develops. They also disagree on the amount of cold air available when the precip develops. The NAM has come in with enough cold air and precip for accumulating snow across the area. The GFS remains cold enough for snow; however, it has shifted the precip axis to our east limiting the amount of significant snow to our southern and eastern CWFA boundary. The Canadian remains warm enough for rain for all the mountains but has shifted the precip axis to the east. The ECMWF continues to be cold enough, but is basically dry with all the precip to our east. The GEFS mean continues to shift the precip axis east but has enough for light snow over our area. The Canadian ensemble mean also trends with light snow at most. Therefore, confidence remains low but the chance of accumulating snow continues. The model blend, and our forecast given the uncertainty, shows an inch of snow basically along and east of a Greenwood- Spartanburg-Hickory line with lower amounts to the west. The eventual result will be highly dependent on the precip axis and cold air availability, so keep up with the latest forecasts for likely changes.

Key message 5: Another cold air mass will settle over the region through the middle next week. A Cold Weather Advisory might be needed for parts of the mountains Monday night into Tuesday.

In the wake of the strong wave moving past Sunday, we should remain at the bottom of a deep long wave upper trof through the first half of next week with a reinforcing short wave Tuesday. This supports a reinforcing cold Canadian sfc high pressure air mass that settles over the Southeast Tuesday behind the already cold air mass for Monday. Tuesday will be the coldest day with highs around 15 degrees below normal. Monday night will be the coldest night, although Tuesday night will be nearly as cold, up to 20 degrees below normal. The low temps combined with the relatively light winds for the mountains will still be cold enough for wind chills to drop into Cold Weather Advisory levels for much of the NC mountains Monday night and Tuesday morning. A slow warming trend takes place Wednesday through Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: Expect dry, VFR conditions to prevail thru the 18z taf period. Any lower clouds in the vicinity of KAVL should remain few to sct this aftn/evening. Otherwise, other than a few high clouds, expect mostly clear skies thru the period. Winds will remain gusty thru the aftn, with gusts dissipating at most sites this evening. Outside the mtns, wind directions will back from N/NW to eventually south of west over- night with speeds of 5 kts or less. Winds will pick back up from the S/SW tomorrow aftn with more low-end gusts expected. At KAVL, winds will remain NWLY and gusty thru the evening. Gusts should dissipate later tonight, with them going light and VRB overnight. Winds at KAVL will toggle around to SLY by the end of the taf period tomorrow.

Outlook: Precipitation and associated restrictions may return this weekend, but confidence remains low on timing.

GSP WATCHES/WARNINGS/ADVISORIES

GA...INCREASED FIRE DANGER until 7 PM EST this evening for GAZ010- 017-018-026-028-029. NC...INCREASED FIRE DANGER until 7 PM EST this evening for NCZ035>037-056-057-068>072-082. Wind Advisory until 7 PM EST this evening for NCZ033-049-050- 053. Cold Weather Advisory until 7 AM EST Friday for NCZ033-048>052- 058-059-062-063. SC...INCREASED FIRE DANGER until 7 PM EST this evening for SCZ008>014-019-101>109.