textproduct: Greenville-Spartanburg

SYNOPSIS

Cool high pressure lingers over the area through Saturday. Then an arctic cold front will cross the region early Sunday, ushering in very cold temperatures to start the week. Temperatures quickly rebound by the middle of next week.

NEAR TERM /THROUGH SATURDAY/

As of 633 PM EST Friday:

Key Message #1: Clearing skies this evening with dry conditions through tonight.

A subtle shortwave embedded in much broader cyclonic flow aloft is now analyzed well east of the area as we head into tonight. Clouds are clearing quickly behind the shortwave and should remain that way through the rest of the night outside of the immediate Tennessee border in the northern mountains. Good radiational cooling conditions will lead to overnight lows dropping approximately a category below normal.

Key Message #2: Warmest day so far in December expected Saturday, ahead of an Arctic Cold Front.

The flow aloft will flatten Saturday while backing from a west-northwesterly component to west-southwesterly in response to a digging closed upper low over the northern Great Lakes region. This shift will allow for subtle height rises as a weak downslope component develops with some compressional warming as well ahead of the Arctic Front in the short-term period. As a result, afternoon highs are forecast to run up to 5 degrees above normal, with locations across the Upper Savannah River Valley and Lakelands likely exceeding the 60 degree mark.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/

As of 1235 PM EST Friday:

Key Message 1: Light precipitation possible Saturday night ahead of an arctic front.

An upper-level polar vortex will sling a strong vort max thru the Ohio Valley to the Carolinas Saturday night thru Sunday. This will bring an arctic cold front thru the Southern Appalachians Saturday night and the rest of the CWFA Sunday morning. Shallow moisture along/ahead of the front may produce a few rain showers overnight Saturday night, with some lingering upslope showers near the TN border thru late Sunday morning. A dusting to up to an 1 inch of snow will be possible in the high elevations of the TN border counties, but otherwise, with generally a trace of rain elsewhere. Little to no impacts expected, but if roads manage to get wet anywhere in the mountains, temps will begin to plummet by daybreak Sunday and could flash-freeze into some black ice. Mountain temps are not expected to warm above freezing the rest of the day.

Key Message 2: Arctic front brings gusty winds with bitterly cold temperatures Sunday through Monday.

An Arctic air mass spills into the area during the day Sunday and continues thru Sunday night. Strong low-level CAA will help mix down gusty winds, with high elevations likely to see gusts over 40 mph from before daybreak Sunday thru early Sunday evening. Gusts east of the mountains of 25-35 mph will be possible Sunday aftn thru early Sunday evening. Winds will begin to weaken Sunday night, but remain breezy and combine with bitterly cold temps to produce wind chills in the +5 to -15 degrees F range across the mountains (and even colder on the highest ridgetops). Confidence continues to increase that a Cold Weather Advisory will be needed for portions of the mountains. East of the mountains, temps will fall into the teens to lower 20s with wind chills in the lower to mid teens. While these are certainly the coldest temps and wind chills of the season so far, they do fall a few degrees short of records or Cold Advisory criteria (outside the mountains).

Winds will continue to subside Monday, but temps will struggle to get into the upper 30s to lower 40s despite sunny skies. Highs should get above freezing everywhere, except perhaps the highest peaks.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

As of 1245 PM EST Friday:

1) Cold air quickly exits the area with temperatures rebounding by the middle of the week.

The center of arctic high pressure will cross the Central Appalachians to the Carolina Coast by Monday evening under flattening flow aloft. This should result in clear skies and light wind across the region, allowing for good radiational cooling. Undercut the NBM min temps with MOS and the NBM 25th percentile for lows Monday night. This results in another chilly night, but not as cold as Sunday night. Temps rebound nicely Tuesday, as return flow picks up behind the departing high pressure. Highs back to lower to mid 50s in the mountain valleys and Piedmont (40s in the high elevations). Dry weather continues Wednesday with zonal flow aloft. Temps continue to moderate back to near or even slightly above normal.

2) Precip chances may return by the end of the week.

Models diverge on depiction of an upper trough digging across the central CONUS late Wednesday into Thursday. The 12z GFS showing a very flat and fast-moving trough seems to be more of an outlier solution, with the ECMWF and Canadian showing a deeper and slower trough. Their solutions brings a cold front thru the area Thursday into Thursday night. The front would likely be too warm for anything but rain, except perhaps some wintry p-types in the highest elevations. The NBM PoPs ramping up into the chance range Thu-Thu night looks good. Temps will remain near to slightly above normal Thursday, then likely cool to slightly below normal Friday (the latest NBM temps look a little too warm).

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR on tap for the 00z TAF period. A bank of mid-level altocu is visible satellite imagery along and north of I-40, but guidance generally suggests it'll retreat northward overnight, giving way to SKC/FEW cirrus for the remainder of the TAF period. Light and variable winds overnight will give way to a steady 5-7kt SW breeze during the daylight hours Saturday.

Outlook: A strong cold front will bring some cloud cover Saturday night into Sunday, but most terminals should remain dry with no real indications of associated vsby/cig restrictions. Very gusty winds are expected late Saturday night through the daytime period Sunday. Dry high pressure will keep VFR conditions in place through the early part of next week.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.