textproduct: Greenville-Spartanburg

SYNOPSIS

A cold front crosses our region from the northwest this evening as colder air filters into the mountains with snow forecast tonight along the Tennessee border areas. High pressure returns Thursday and into the weekend ahead of an arctic cold front which arrives early Sunday. Dry and cold high pressure will move in briefly for the start of next week.

NEAR TERM /THROUGH THURSDAY/

As of 640 PM EST Wednesday:

Low clouds and some spotty precip are crossing the area ahead of the cold front approaching from the northwest. Steadier precip will move into the mountains in the moist, NW flow behind the front this evening. Clouds will linger across the mountains as well. The clouds should scatter out outside of the mountains later this evening as the across the Ozark Plateau and into extreme eastern Arkansas. front moves through.

Key Message #1: Winds diminish outside of the mountains but remain windy across the North Carolina mountains.

The cold front moves into the area this evening. Windy conditions will continue across the mountains overnight with very windy conditions above 3500 feet. Winds have diminished outside of the mountains but low end gusts will continue through the evening as the front crosses the area.

As a result, a Wind Advisory remains in place for elevations above 3500ft, valid through 10AM Thursday.

Key Message #2: Temperatures cool to below normal tonight.

The onset of aggressive postfrontal CAA tonight will rapidly lower temperatures, with most of the mountains falling quickly into the 30s, and the entire forecast area seeing lows at least a category below normal Thursday morning. Those below-normal temperatures will stay in place into Thursday, with highs only climbing into the upper 40s across the low terrain, some 2 or more categories cooler than normal!

Key Message #3: Wintry precip develops across the North Carolina mountains tonight, producing accumulating snowfall at higher elevations.

Deep moisture will quickly fill into the area. As soon as temperatures can cool enough this evening (see key message #2 above), locations across the mountains should change over from rain to snow...with virtually all of Appalachia expected to see at least flurries by midnight. While lower elevations may see no accumulation, or only a dusting, higher elevations could see 2-3" through Thursday morning, and isolated locations across the northern Blue Ridge could see totals in excess of 4".

Therefore, Winter Weather Advisory is in place for Avery County and elevations above 3500ft for the rest of the northern mountains and Madison County. It will continue through 10AM Thursday, expiring alongside the Wind Advisory.

SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/

As of 1236 PM EST Wednesday...

Key Message #1: Most locations remain dry outside of a passing clipper system over the northern mountains on Friday.

Weak cyclonic flow aloft will be in place during the short-term period, with a passing shortwave to the north on Friday. Guidance gradually shifting south and clipping the northern mountains with light rain/snow and little to no accumulations expected at this time. Otherwise, the airmass is expected to modify with high pressure moving in with highs at or slightly below normal. Overnight lows will be a few ticks below normal for both Thursday and Friday.

Key Message #2: Above normal temperatures on Saturday

Rising heights and compressional warming ahead of a strong cold front will allow for temperatures to rise a few ticks above normal for Saturday. Model guidance vary on the overall arrival of the front, but the consensus is that the front should remain just northwest of the CWFA by 00Z Sunday, allowing for only increasing high clouds by the very end of the forecast period.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

As of 105 PM EST Wednesday...

Key Message #1: Model guidance continue to trend toward a dry frontal passage Saturday night into Sunday, cold and breezy behind the front.

Strong cold front will be in the midst of moving across the CWFA Saturday night as a digging closed upper low moves across the Great Lakes region. The better forcing for ascent and available moisture will be allocated closer to the core of the low and along the Gulf Coast, leading to a dry fropa. Most of the guidance indicates that the full fropa should occur by 12Z Sunday with low-level CAA rushing in behind the front across the mountains, but expecting the typical downslope delay outside of the mountains during the daytime period Sunday. A strong continental surface high (~1040mb) will be in the midst of sliding across the central CONUS with a brief window of opportunity for northwest flow snow along the immediate TN border before dry air entrainment shrivels the shallow low-level moisture layer. Very tight pressure gradient will develop over the mountains behind the front and suggests that near Advisory criteria gusts develop over the high terrain starting Sunday morning and linger throughout the day before gradually subsiding overnight Sunday as the center of the surface enters the central/southern Appalachians by Monday morning. Overnight lows on Saturday night should run a few ticks above normal with weak WAA ahead of the front. Afternoon highs will run 15-20 degrees below normal across the mountains, while locations outside the mountains only run 5-10 degrees below normal thanks to the aforementioned delay to the CAA onset. However, CAA will be in full affect across the CWFA Sunday night with a nice shot of Arctic air, leading to overnight lows running 15-20 degrees below normal, with single digits in the highest elevations, teens elsewhere in the mountains, teens and twenties outside of the mountains. Wouldn't be surprised if a Cold Weather Advisory needs to be issued for the northern mountains when factoring the lingering gusts with the very cold airmass in place.

Key Message #2: Cold on Monday with a modifying airmass by Tuesday and Wednesday

Monday will be the coldest day of the seven day forecast period as the arctic airmass settles in fully with the continental high centered over the area, leading to afternoon highs running 10-15 degrees below normal. The best radiational cooling conditions are expected to be Monday night as values continue to run 10-15 degrees below normal. However, the airmass should modify rather quickly as a shortwave ridge builds in on Tuesday following the departing shortwave trough as the surface high drifts offshore. With warmer thicknesses moving in across the region expect afternoon highs to warm, but hover at or a few ticks below normal Tuesday and Wednesday. A southern stream system looks to try and get its act together by the middle part of next week, but guidance differ this far out on the overall synoptic outlook and timing on everything.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Low VFR clouds spreading in from the northwest with a cold front crossing the area. Outside of the mountains, these should scatter out by midnight or so. Winds have diminished but gusts will continue as the direction shifts from the SW to NW outside of the mountains. KAVL already NW and will go NNW with stronger gusts returning overnight. Some LLWS will continue as the southwest low level jet moves out but stronger northwest low level winds move in with the front. Any LLWS should abate by daybreak. Rain showers and MVFR conditions are possible at KAVL this evening. Cigs go solidly MVFR overnight as moisture is forced up the valley in the NW flow. Can't rule out a flurry, but chance too low for the TAF. Cigs scatter out around daybreak. Lighter NW wind expected Thursday, but gusts will linger at KAVL. Winds outside of the mountains turn more SW late in the day.

Outlook: A clipper type low pressure system could bring clouds and light precip to the mountains Friday. Dry, VFR conditions expected Saturday. Another clipper type low pressure system could bring clouds and precip Saturday night and Sunday, along with very gusty winds. Dry high pressure returns Monday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Wind Advisory until 10 AM EST Thursday for NCZ033-048>053-058- 059-062>064. Winter Weather Advisory until 10 AM EST Thursday for NCZ033- 048>050. SC...None.