textproduct: Greenville-Spartanburg

SYNOPSIS

A cold front moves to the Carolina coast today. Much colder temperatures arrive behind the front and continue into the weekend. Another cold front arrives Sunday with a secondary low pressure system on Tuesday.

NEAR TERM /THROUGH TONIGHT/

As of 1116 PM Tuesday: A potent negatively tilted trough extending through the Midwest and into the Appalachians will lift across the Great Lakes and into New England today and tonight. A band of showers supported by upper divergence in the right entrance region of an upper jet continues to slowly slide across the area and will persist through the early morning hours. With time, this activity will move off to the east by daybreak. Rain cooled air has kept a stable airmass in place across much of the forecast area today and into this evening with destabilization and surface-based instability confined well to the south/southwest. While a few isolated lightning strikes cannot be ruled out, thunderstorms and any severe weather potential are generally not expected. Clouds will lift and scatter through the morning after sunrise, but the actual surface cold front will still be located off to the west and isn't forecast to move into the mountains until very late morning into the early afternoon. This will allow for yet another warm day, especially with compressional heating ahead of the boundary. Afternoon highs will return to the mid 60s to low 70s with a few readings potentially pushing back into the mid 70s. The front is progged to have moved through the area by this evening with cold advection quickly ramping up in its wake. Overnight lows will fall into the mid 20s to mid 30s by Thursday morning with gusty winds. A sharp pressure gradient across the mountains and strong 850mb flow will support a window for advisory level gusts of 40-50kts (45-55mph) across the higher elevations of Yancey, Mitchell and Avery counties. A subsequent wind advisory has been issued for Wednesday night into Thursday morning.

SHORT TERM /THURSDAY THROUGH SATURDAY/

As of 1230 AM EST Wednesday: A deep trough starts out over the area and then slowly moves east through the period with the flow becoming zonal then southwesterly by Saturday as a short wave moves into the Mid-South. At the surface, a tight pressure gradient will be over the area through Thursday night before relaxing Friday as the center of surface high pressure approaches from the west. The high settles into the area Friday night then the center moves off the Mid Atlantic coast Saturday with a ridge over our area in a CAD configuration. Windy to breezy conditions remain over the area through Friday. A very dry air mass moves in as well with RH falling below 25% for much of the area. The strongest winds and lowest RH don't overlap, but there may be enough of an overlap for Increased Fire Danger, especially Friday after drying takes place on Thanksgiving Day. Coordination with land managers may be needed. The low RH continues Saturday but winds will be much lighter. The other story is the cold air mass moving in. Highs will be 5 to 10 degrees below normal on Thanksgiving, dropping to 10 to 15 degrees below normal Friday and Saturday. Lows around 10 degrees below normal Thursday night fall to 10 to 15 degrees below normal Friday nite.

LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/

As of 1255 AM EST Wednesday: Forecast confidence remains low in this period as guidance disagrees on the next storm system due to variances in the developing split flow regime.

In general, a cold front attached to a northern stream low over the Great Lakes and a southern stream Gulf low moves into the area during the Sunday time frame and to our east in the Monday time frame. A second southern stream Gulf low takes on a Miller A look in the Tuesday time frame. The timing and thermal profiles of these systems differs among the models and ensembles. If the precip ahead of the front could move in fast enough Saturday night, cold air lingering in the mountain valleys and near the Blue Ridge could help create some freezing rain or a wintry mix before the stronger warm nose and warming surface temps kick in changing all the precip to rain. If the precip onset is late, then only rain is expected. Even with the earlier onset, wintry accums would be limited and very light.

Precip briefly tapers off Monday before returning with the second wave on Tuesday. A hybrid CAD develops which would keep temps on the cold side. Still, the guidance differs with some showing just rain at onset while others show another brief period of freezing rain before going to all rain. Depending on how fast the low moves, NW flow snow could develop by late Tuesday or could be delayed until later. For now, the potential wintry precip Tuesday morning would again be limited and very light if it develops.

Lows below normal Saturday night warm to around 5 degrees above normal for the rest of the period. Highs 5 to 10 degrees below normal Sunday, rise to a few degrees below normal Monday, then back down to 5 to 10 degrees below normal Tuesday. Temps dependent on the strength of the wedge and precip timing.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: This morning starts off marked by poor flying conditions as a low stratus deck has brought a myriad of issues along with fog, some of which is locally dense. Ceilings vary from MVFR to IFR with several terminals socked in pretty good with dense fog. The good news is that conditions should improve fairly quickly through the morning as fog mixes out and the low stratus lifts and scatters. This will bring a return to VFR by mid to late morning at all terminals. VFR will prevail thereafter with the main focus shifting to winds. Frequent gusts from the southwest are expected through this afternoon ahead of an advancing cold front. Winds will shift to out of the northwest behind the front as it drops across the area late this afternoon into this evening.

Outlook: Drier and predominantly VFR conditions should linger through the end of the week.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Wind Advisory from 7 PM this evening to 11 AM EST Thursday for NCZ033-049-050. SC...None.