textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Slight uptick in rainfall amounts for late Friday into Saturday afternoon with the next disturbance.

Updated for the 18Z TAFs.

KEY MESSAGES

1. The next weather-making disturbance will track along the Gulf Coast and into the western Atlantic on Friday and Saturday, bringing a round of beneficial rainfall to the western Carolinas late Friday through Saturday afternoon. 2. Below-normal temperatures will settle over the region Saturday night, with the potential for areas of frost in the mountain valleys and foothills, and freezing temperatures in the highest elevations. Dry weather and a warming trend back to above normal temperatures expected through Tuesday. 3. Another cold front may bring rain chances to the area by the middle of next week, but forecast confidence remains low.

DISCUSSION

Key message 1: The next weather-making disturbance will track along the Gulf Coast and into the western Atlantic on Friday and Saturday, bringing a round of beneficial rainfall to the western Carolinas late Friday through Saturday afternoon.

Mostly dry conditions and temperatures near-normal expected for today, followed by continued dry weather and cooler conditions tonight. Model guidance still in really good agreement showing a surface wave traveling along a baroclinic zone over the Deep South and Gulf Coast, bringing better moisture return into the area during the day Friday. Very good moist upglide and right entrance upper- level divergence should promote the onset of widespread drizzle and showers starting late Friday through the first part of Saturday. Any severe weather will remain well south of the CWFA as the warm sector remains over Florida and off the Southeast Coast. Most of the precipitation will be beneficial stratiform, with some instances of convective elements possible if elevated instability can develop. Saturday will be a very cloudy and dreary day with afternoon highs barely making it to the 60 degree mark outside of the mountains. The surface low will exit off the Outer Banks by Saturday afternoon, leading to surface CAA on the backside and will virtually put an end to the precipitation. A relatively tight gradient for precipitation amounts seem evident as locations along and south/east of I-85 could pick up a half inch to an inch, with locally higher amounts. Locations north and west of I-85 trend lower the further away from the coast you are. With persistent light to moderate rainfall over roughly an 18-24 hour period, it will seem like more rain than it actually is. Guidance still are back and forth on total QPF amounts, so expect adjustments through Friday.

Key message 2: Below-normal temperatures will settle over the region Saturday night, with the potential for areas of frost in the mountain valleys and foothills, and freezing temperatures in the highest elevations. Dry weather and a warming trend back to above normal temperatures expected through Tuesday.

The axis of a deep upper-level trough will swing across the Appalachians Saturday night, then will be followed by relatively flat flow thru Tuesday. A cool, dry high pressure system will build in from the west, but the sfc ridge axis will still be over the OH to Lower MS Valley thru 12z Sunday. This will keep a pressure gradient over the CWFA, which may prevent winds from completely decoupling. However, confidence is increasing that the mountain valleys and the foothills near the Escarpment will be sheltered from the NWLY flow and will see good radiational cooling for frost development. Also, an advective freeze above 3500 ft will be possible, although guidance is not in great agreement on the 850 mb temps thru 12z Sunday, but most members show 0 to -2.5 deg C along the TN border. A combination of Freeze Warnings and/or Frost Advisories may be needed for Saturday night across most of the mountains and possibly into the NC foothills. Temps elsewhere will be in the upper 30s to lower 40s.

Temps should start a steady warming trend Sunday thru Tuesday, as high pressure crosses the area and brings a SWLY flow atop the region. Dewpts will also gradually recover, but minimum RH values may dip into the 25-35% range each aftn in the lower elevations with marginally breezy conditions. Depending on how much fine fuels can dry out, there may be some fire weather concerns Monday and Tuesday. Guidance is in good agreement on no mentionable PoPs thru 00z Wed.

Key message 3: Another cold front may bring rain chances to the area by the middle of next week, but forecast confidence remains low.

Models still in disagreement on how quickly and how deep an upper trough digs into the Upper Midwest late Tuesday into Wednesday, before carving out a large long-wave trough over the eastern CONUS by late next week. This trough should bring a cold front in from the west, likely crossing the CWFA Wednesday or Thursday. The GFS is on the faster and shallower side of the deterministic guidance, and brings moisture and the cold front into the forecast area by Tuesday night. The ECMWF has precip chances returning Wednesday aftn in the mountains and the rest of the area Wednesday night. The Canadian is even slower, and has a narrower band of precip with the front on Thursday. All that to say, confidence remains low on how quickly PoPs will ramp up in that time frame, but at least some period of rain is likely for the CWFA by next Thursday. Confidence is even lower on how much rainfall will occur with this front. The latest model consensus if for generally 0.25-0.5" of QPF, with 0.5-1.0" in the SW-facing slopes of the mountains south and west of the French Broad Valley. Temps will remain slightly above normal thru Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: An end to the line of showers and storms from this morning has lead to partly to mostly sunny skies with VFR prevailing at all sites. Winds are variable, but favoring a north to northeasterly direction this afternoon, while KAVL maintains a north- northwesterly wind with 20-25 kt gusts. KAND will remain mostly westerly through the afternoon. Winds go light north to northeast during the evening and overnight with increasing mid and high clouds ahead of the next disturbance. VFR cloud cover will remain in place on Friday as winds turn the dial during the morning hours before fully coming around out of the south and southwest by the afternoon.

Outlook: Another disturbance brings rain chances and associated restrictions Friday evening into Saturday. Dry and VFR conditions return Sunday and linger through at least Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

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