textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Heat indices have trended down slightly for today.

Updated discussion for the 12z TAFs.

KEY MESSAGES

1. Scattered showers and thunderstorms expected this afternoon into early evening. A few storms will pose a damaging wind threat. Today will be the last hot and muggy day before a cold front pushes through the area tonight. 2. Drier and slightly below-normal temperatures Monday trough Wednesday, with moisture and rain chances increasing in the second half of the week.

DISCUSSION

Key message 1: Scattered showers and thunderstorms expected this afternoon into early evening. A few storms will pose a damaging wind threat. Today will be the last hot and muggy day before a cold front pushes through the area tonight.

A remnant MCV/vort-max currently over central TN will enter the southern Appalachians around midday today, helping trigger convection across the NC mountains. The CAMs have not initialized convection associated with the MCV very well, but the HRRR has been picking up on it in recent runs. It has the greatest coverage of storms across the mountains this aftn, then showing scattered activity tracking east across the NC Piedmont and northern Upstate. Modest instability and 20-30 kt of 0-6 km bulk shear may be enough to cause some organization of multi-cell clusters around outflows. More mid-level moisture from upstream convection may result in lower DCAPE, which may limit severe wind potential somewhat. Nevertheless, a few severe storms producing damaging wind gusts still looks on tap for the area. The new Day 1 Convective Outlook still has the entire area in a Slight Risk.

Otherwise, it will be another hot and humid day. The latest NBM has trended down slightly on max temps, possibly due to convection developing before max heating. Also, dewpts are expected to mix out into the 60s again across most of the area, helping keep heat indices mainly in the 90s outside the mountains, with 100-104 possible in the Charlotte metro area. Convection should exit to the east late this evening, but additional showers and possibly isolated thunderstorms are shown on the CAMs developing near the sfc front as it pushes in from TN. This activity is not expected to be strong and not expected to survive east into the Piedmont.

Key message 2: Drier and slightly below-normal temperatures Monday trough Wednesday, with moisture and rain chances increasing in the second half of the week.

A cold front will push thru the area by daybreak Monday, ushering in cooler, and drier air for the first half of the week. Temps a little below normal combined with dewpts dropping into the 50s to lower 60s will feel rather comfortable compared to what we've experienced the last few days. Model consensus is for generally dry weather, except for some slight chc to low-end chc PoPs sneaking into the far southern parts of the forecast area, as the front stalls out not to far south. A series of shortwaves will ride through the broad upper trough and could trigger some lift over the stalled front and bring moisture northward.

The latest deterministic models are in better agreement on the pattern late in the week. They show the trough flattening out, but lingering enough to possibly allow a tropical disturbance (or at least enhanced tropical moisture) to lift north into the NW Gulf and interact with the stalled frontal zone near the Gulf Coast. Meanwhile, another cold front will drop southeast across the Midwest to the Ohio Valley, likely reaching the CWFA on Friday. Not surprisingly, the NBM has PoPs increasing Thursday, and peaking to likely to categorical PoPs on Friday. As far as severe and heavy rain threats, confidence remains low this far out. Temperatures return to slightly above normal.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Confidence remains below average for timing of convection today, as guidance shows scattered showers and storms forming with a leading disturbance early aftn, then another round possible in the evening with a cold front. Still expect the first round to be stronger, but some guidance is trending toward second round having more coverage. Did not make major changes to the PROB30s for TS today. Winds will pick up out of the SW and become gusty east of the mountains, with gusts around 20 kt expected. There is potential for at least a few gusts approaching 25 kt during mid to late aftn in the Upstate and at KCLT. Winds will weaken this evening, toggling to WSW, except NW at KAVL. The cold front will pass through KCLT by around 12z Monday, shifting the winds out of the NW. Behind the front, MVFR clouds may work up the valley to KAVL overnight with breezy north winds.

Outlook: Quiet conditions expected Monday thru midweek. Valley fog and low stratus is possible each morning, primarily in the mountain valleys. Diurnal convection may return to the region Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

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