textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes to the general forecast.

The aviation forecast was updated to reflect the recent 06Z TAF issuance.

KEY MESSAGES

1. Hot and muggy conditions persist through the end of the week. Some relief arrives this weekend. 2. Diurnal showers and storms return Thursday, and persist through the end of the week. Drier conditions arrive again by Sunday.

DISCUSSION

Key message 1: Hot and muggy conditions persist through the end of the week. Some relief arrives this weekend.

A weakness in the subtropical ridge remains in place over the Southeast tonight, on the periphery of a much deeper upper low centered over eastern Canada. Still don't expect much change to this configuration over the next few days; at the surface, weak N/NE flow will continue behind Monday night's cold front, keeping dewpoints constrained and resulting in upper-90s to lower-100s heat index values this afternoon, and again Thursday and Friday afternoons. Still unpleasantly hot and muggy, but not quite into the danger-zone that would prompt a Heat Advisory.

Guidance continues to depict another cold front arriving on Saturday night or Sunday, but true to form, deterministic models have waffled once again, toward a stalling front in or south of the GSP forecast area. Long-range ensembles still feature a mix of both this scenario and the previously-favored scenario in which the front makes a complete passage, drying us out Sunday afternoon into Monday. Either way, much of the region could see some relief from the heat over the weekend as the front arrives and ushers in somewhat a somewhat cooler and drier air mass.

Key message 2: Diurnal showers and storms return Thursday, and persist through the end of the week. Drier conditions arrive again by Sunday.

A closed h50 low will meander from the Hudson Bay eastward across Quebec and into the northwestern Atlantic through the end of this week. A series of embedded vort lobes will rotate around it; they'll generally stay to our north but should nonetheless act to reinforce the troughiness already in place across the Carolinas. A cold front, meanwhile, will settle across the Ohio Valley by late Wednesday, providing the impetus for organized convection well upstream. The 00Z suite of hi-res guidance almost universally depicts a decaying MCS sliding across Kentucky and eastern Tennessee early Thursday morning, and making a run at the Tennessee border; confidence remains low on how much of a severe threat this will pose, as given the currently-forecast arrival time near the diurnal min, conditions won't be favorable for it to maintain its integrity crossing the Appalachians.

Thereafter, expect a return to more seasonable diurnal convection on Thursday and Friday afternoons. Both afternoons, but especially Friday, will feature some degree of non-negligible shear as the cold front and associated h50 westerlies draw closer to the area (perhaps even settling into the mountains by Friday afternoon or evening), so still think some degree of weakly-organized convection will be possible, instead of the completely disorganized pulse convection we'd see in a less-dynamic environment. So, will need to continue monitoring the severe threat late this week.

Timing inconsistencies continue to plague the 00Z long-range ensembles; it remains questionable where the front will be by Saturday afternoon. Whether it has shifted to our east, or remains in our area, will moderate convection chances for Saturday. Confidence is higher that by Sunday and Monday, we'll start to see an influx of drier postfrontal air, resulting in a cooldown and suppressed afternoon convection Sunday and Monday. Details remain a little murky, however...so stay tuned.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR on tap for the 06Z TAF period. Other than the potential once again for some IFR to LIFR valley fog and low stratus across the North Carolina mountains, which should only impact KAVL for a few hours before dawn...if at all...the TAFs are VFR, featuring FEW cirrus, perhaps a brief afternoon cu field on Wednesday, and a steady 4-8kt N wind through the period.

Outlook: Scattered diurnal convection is expected to return on Thursday, with afternoon showers and storms possible each day through Saturday. Low stratus and fog will be possible each morning, mainly in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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