textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to the public forecast. The Aviation section has been updated for the 00z TAFs.

KEY MESSAGES

1. Seasonally hot and humid east of the mountains through Saturday, then a slight cool-down for Sunday and Monday. Though a Heat Advisory is not likely to be issued, those with outdoor plans should stay hydrated and take frequent breaks in air-conditioned or shaded areas. Never leave children or pets in unattended vehicles. 2. Diurnal showers and thunderstorms are expected across mainly western North Carolina through Friday before a cold front brings better shower and thunderstorm chances area-wide this weekend into Monday. A few strong to possibly severe storms are possible during peak heating hours each day through Friday, with damaging wind gusts being the main hazard with any severe storms that manage to develop.

DISCUSSION

Key message 1: Seasonally hot and humid east of the mountains through Saturday, then a slight cool-down for Sunday and Monday. Though a Heat Advisory is not likely to be issued, those with outdoor plans should stay hydrated and take frequent breaks in air-conditioned or shaded areas. Never leave children or pets in unattended vehicles.

The Bermuda High slowly breaks down through the end of the week and will be replaced by a weak upper trof that will support increasing storm coverage, yet temps will remain seasonally hot through Saturday...generally five degrees or so above normal. Typical summertime humidity will also continue to be a factor, but dewpoint is expected to mix out enough to keep us from reaching Heat Advisory criteria each afternoon. Model guidance continues to show a bit more breezy than usual in the afternoons, which might feel like a bit of a relief, but more likely the relief will come from showers and storms. By the weekend, a weak front will drop down into the region courtesy of a short wave in the nrn stream, which will eventually push the front through perhaps on Sunday. The increase in storm coverage and cloud cover may drop the temps back to normal Sunday, but more likely that will happen for Monday. There remains plenty of uncertainty as to the development of weak cold air damming early in the week because of a transitory sfc high moving across New England, but for now we will keep the below normal temps Monday. Some of the guidance suggests the cooler air will linger into Tuesday. Welcome relief...if it develops.

Key message 2: Diurnal showers and thunderstorms are expected across mainly western North Carolina through Friday before a cold front brings better shower and thunderstorm chances area-wide this weekend into Monday. A few strong to possibly severe storms are possible during peak heating hours each day through Friday, with damaging wind gusts being the main hazard with any severe storms that manage to develop.

For the afternoon, the main concern is the Marginal Risk of severe storms over the northwest Piedmont and northern part of metro Charlotte, but really anywhere east of the mountains where storms develop. The environment is characterized by sfc-based CAPE in the 2000-3000 J/kg range, but with dCAPE above 800 J/kg everywhere east of the mtns, and sfc-delta theta-e around 30K. Thus, the environment is supportive of wet microbursts outside the mtns, even if the HRRR shows the convective activity mainly over central NC.

More of the same is expected for Thursday and Friday, with improving coverage each day, above climo, and favoring the mtns the most even if the pulse-severe risk might be slightly higher east of the mtns. The main hazard with any severe storms will remain damaging wind gusts from microbursts. As the coverage improves, the flash flood risk will also increase over mainly the NC mountains as we get into this weekend and the boundary sinks down into the region. Precipitable water will climb up into the 2 inch vicinity which is approaching the top end of the climatology. Note the Day3-5 Excessive Rainfall Outlook has a slight risk in the TN valley into the west side of the mtns, so we will be watching that situation. Drier conditions should return by Tuesday as surface high pressure builds into the region behind the departing front.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Widely scattered showers and storms will continue to dissipate over the next several hours with no additional impacts expected at area terminals. A quiet evening is expected with only focus being on the potential for another round of mountain fog and stratus. Restrictions may be possible at KAVL through the predawn hours before any fog mixes out. Thereafter, gusty southwest winds return Thursday afternoon with another round of scattered afternoon showers and thunderstorms, mainly across North Carolina. Associated visibility and ceiling restrictions will be possible with any storms that develop.

Outlook: The NC terminals will have the best potential to see TSRA each afternoon and evening through Friday. SHRA/TSRA chances return for all terminals this weekend into Monday. Low stratus and/or fog will be possible each morning in the mountain valleys and in locations that see appreciable rainfall the previous afternoon/evening.

GSP WATCHES/WARNINGS/ADVISORIES

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