textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00Z TAFs.

KEY MESSAGES

1. Dry through Friday before another disturbance brings rain chances back Friday evening into Saturday. Below normal high temperatures can be expected each afternoon, especially on Saturday. 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: Dry through Friday before another disturbance brings rain chances back Friday evening into Saturday. Below normal high temperatures can be expected each afternoon, especially on Saturday.

Dry conditions linger through most of Friday. Model guidance remain in agreement that a surface wave traveling along a baroclinic zone over the Deep South and Gulf Coast will bring better moisture return into the area late Friday into the first half of Saturday. Moist upglide and right entrance upper-level divergence should promote the onset of light rain starting Friday evening, with rain blossoming further Friday night into early Saturday morning. A relatively tight precipitation gradient is expected and could end up roughly along the I-85 corridor. Locations along and south of 85 will see the highest rainfall totals, with amounts ranging from 0.50" to 1". Locally higher amounts will be possible across the far southern South Carolina Upstate. Areas north of 85 will see lower rainfall totals, with most locations receiving less than 0.50". However, if the precipitation gradient ends up setting up farther south, rainfall amounts will be lower area-wide. Any severe threat will remain well south of the GSP CWA as the warm sector remains over Florida and off the Southeast Coast. Dry conditions should return by early Saturday afternoon. Highs on Friday will end up ~5 degrees below normal thanks to cloud cover. Highs on Saturday will end up ~15 degrees above normal thanks to both rain and cloud cover.

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 /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Dry and VFR with BKN to OVC cirrus expected through the 00Z TAF period. Winds east of the mountains start out NNW/N this evening before turning NE late this evening into daybreak Friday. Winds east of the mountains will gradually turn S/SSW Friday morning into Friday afternoon. Winds at KAVL will start out NNW with gusts lingering through the early evening hours before tapering off. Wind at KAVL will go calm overnight into daybreak Friday before picking up out of the SE by mid-morning. Winds at KAVL should turn back to the NW by early Friday evening.

Outlook: A disturbance brings rain and associated restrictions back to the terminals Friday evening into Saturday. Dry and VFR conditions return by Sunday and linger through at least Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

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