textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Adjusted PoP this evening for current and expected conditions.

Updated for 00Z aviation discussion.

KEY MESSAGES

1. Above normal temperatures with daily chances for showers and thunderstorms through Saturday. 2. Cold front Saturday night and Sunday will increase the chance for more appreciable rainfall. 3. Frost/freeze conditions possible in the mountains early to middle of next week.

DISCUSSION

Key message 1: Above normal temperatures with daily chances for showers and thunderstorms through Saturday.

Upper ridge associated with Bermuda High already in place across the coastal Southeast, and is expected to strengthen, remaining the dominant feature in our weather through Saturday. Synoptic scale forcing will remain weak through Saturday as frontal systems are held off to our north and west by the ridge. Southerly flow around the ridge into the southern Appalachians will maintain temperatures and humidity more reminiscent of mid May, with temperatures remaining 10 or more degrees above normal. Diurnally driven convection will be possible each day, the best chances being over the mountains where upslope flow will help trigger development of showers and thunderstorms.

Models have been fairly consistent in showing convective coverage being better this (Wednesday) afternoon and evening than either what was observed Tuesday, or what is projected for Thursday. This is presumably due to enhanced convergence on the western flank of the sfc/upper high and moisture advection into low pressure now over the Northeast. The best overall coverage this afternoon/evening looks to be near the Escarpment; steering flow out of the S to SW suggests ongoing activity in TN is not likely to move into the NC mountains and that precip chances remain low for the Piedmont, as mountain cells should remain more or less over the mountains.

Still seeing a signal from guidance for convection to be suppressed Thursday due to an intrusion of drier air aloft. Chances then trend upward for Friday and Saturday as low pressure systems track across the Midwest and Great Lakes, generally promoting moisture advection aloft that makes deep convection more plausible each afternoon. Despite the moisture aloft, without strong forcing, rainfall is not likely to be enough at any one location to improve drought conditions or lead to anything more than a localized wetting rain that could ease fire weather concerns. Higher minimum relative humidity values should however limit fire danger.

Key message 2: Cold front Saturday night and Sunday will increase the chance for more appreciable rainfall.

Low pressure will develop and move through the Great Lakes states into Canada over the weekend. The low will push a cold front through the area from late Saturday night into Sunday. A band of showers associated with the front will move through the area with this being the best opportunity for widespread appreciable rainfall in the next 7 days.

Key message 3: Frost/freeze conditions possible in the mountains early to middle of next week.

Behind the front for the early to middle part of next week, drier conditions will return with cooler temperatures that are closer to normal for this time of the year.

Morning lows each day will be in the 30s in the mountains, so we will need to watch for frost and/or freeze conditions there. Morning lows will not be cold enough outside the mountains for any concerns through next Wednesday.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Still some convection out there but chance of any moving over a terminal is low. Did include VCSH for all but KCLT where the chance is lowest. S to W wind diminishes through the evening but a brief low end gust is possible early. Low level moisture moves in from the SE overnight. This could lead to MVFR and possibly IFR cigs near daybreak. However, the latest guidance has backed off on the potential. Still, this will need to be watched closely and restrictions are possible. If cigs develop they, should lift/scatter out around noon with VFR expected through the afternoon. The best chance of afternoon convection retreats to the mountains, so only have a PROB30 for KAVL. S to SW wind picks back up during the day with low end gusts possible again.

Outlook: Daily chances for showers and thunderstorms with associated restrictions through the weekend. A cold front will bring greater chances for restrictions Saturday night into Sunday morning. Dry high pressure moves in Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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