textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The wind and gust forecast was tweaked for Friday afternoon, based on recent hi-res model guidance indicating stronger gusts than previously forecast.

The aviation forecast was updated to reflect the impending 00z TAF issuance.

KEY MESSAGES

1. Behind a cold front, dry and mild conditions return through at least Saturday night. 2. Another strong cold front will bring showers and possibly some thunderstorms to the area Sunday night through Monday. A brief period of snow showers will be possible in the highest elevations near the Tennessee border on Monday. 3. Much colder air returns behind a strong cold front Monday night and lingers through at least Wednesday. Most areas will likely see temperatures at or below freezing both Tuesday and Wednesday morning.

DISCUSSION

Key message 1: Behind a cold front, dry and mild conditions return through at least Saturday night.

As the departing cold front continues to march eastward, a much quieter and mild period sets up across the southeast. Drier conditions also return as high pressure moves in. Behind the front, much cooler temperatures as CAA pushes into the area. The daily high was already recorded after midnight ahead of the line, so temps dip into the low 50s and upper 40s throughout the day for locations east of the mountains. Temperatures overnight dip to near freezing outside the mountains and below freezing for the higher elevations. Expect temps to gradually warm into the low to mid 70s through Sunday, ahead of the next system. Drier air Friday and Saturday looks to decrease RH values into the 30-40% range. An upper low passes to the north of the CWA Friday, increasing winds across the area. Current guidance has gusts of 15-25mph, well below any advisory criteria, with the elevated gusts across the higher elevations. All in all, quiet weather through most of the weekend.

Key message 2: Another strong cold front will bring showers and possibly some thunderstorms to the area Sunday night through Monday. A brief period of snow showers will be possible in the highest elevations near the Tennessee border on Monday.

A strong low pressure system will develop over the central Plains Sunday and track into the Great Lakes on Monday. The system will bring a strong cold front thru the OH/TN valleys and reach the Southern Appalachians around 12z Monday. A warm front will activate roughly along the I-20 corridor on Sunday, with some moisture and lift to support rain chances ramping up during the day. This precip may be enough to produce an in-situ CAD, but the wedge is not expected to hold on very long, as a 50+ kt SWLY low-level jet scours out any cold pool. Confidence is increasing that the frontal timing may be slow enough to allow better destabilization during the day Monday across much of the Piedmont. The front will be strongly forced and bulk shear looks to be 50-60 kt along the boundary. The SPC Day 5 convective outlook has a Slight Risk for much of the Mid-Atlantic, extending SW into the NC Piedmont. There is still some uncertainty on the timing, as a slightly faster front will keep the severe threat largely east of the area. Either way, gusty gradient winds are expected both ahead of the front out of the SW, and behind the front out of the NW. These winds will approach advisory criteria in the high elevations. Temperatures will be about 10-15 deg above normal ahead of the front Sunday, staying elevated Sunday night. Confidence on temps Monday is below average due to the fropa, but expected to be about 10 deg above normal in the east, and near to slightly below normal in the far western part of the forecast area.

A brief NW flow snow event will be possible on the back side of the system Monday aftn. Moisture with the NWLY flow looks fairly brief in the latest medium range guidance, with PoPs tapering off quickly Monday evening. Therefore, advisory-level snow accums look unlikely, except for the usual locations along the TN border above 3500 ft.

Key message 3: Much colder air returns behind a strong cold front Monday night and lingers through at least Wednesday. Most areas will likely see temperatures at or below freezing both Tuesday and Wednesday morning.

A deep upper trough will dig into the eastern CONUS Monday and persist thru at least Thursday, as reinforcing shortwaves dive into its axis. This will allow a cold air mass to slide right into the Southeast and bring temps will below normal across the region. The main concern will be a return of freezing temps across most of the CWFA both Monday night and Tuesday night. The latest National Blend of Models has trended a deg or two cooler on average across the area both nights. Lows 10 to 15 deg below normal and highs of 15 to 20 deg below normal expected Tuesday. While the growing season usually does not begin this early, the recent warm weather is likely resulting in some tender vegetation blooming, which may be vulnerable to this cold snap. Temperatures will begin a gradual warming trend Wednesday and Thursday, but remain below normal for mid-March.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Primarily a wind forecast with VFR on tap for the new 00z TAFs. Cold front is now located well to our east off the Atlantic coast, with strong NW CAA winds reported everywhere in its wake. Expect gusts to become increasingly infrequent in the next 1-2 hours before tapering off entirely. Winds should then become light and variable overnight, perhaps favoring the NE the first half of the night and the SE the second half of the night. Expect a S/SW wind to pick up shortly after daybreak Friday, with gusts of at least 20kts expected to develop by late morning and continue through the afternoon.

Outlook: VFR will continue through at least Saturday night. A cold front will bring a round of showers and associated flight restrictions as early as Sunday evening, but as late as Sunday night into Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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