textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

High temperatures have cooled by up to 2 degrees for Monday and Tuesday.

Updated the aviation discussion for the 18Z TAFs.

KEY MESSAGES

1. Hot and humid conditions remain in place for most of the week, mainly east of the North Carolina Mountains. 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. Daily showers and thunderstorms are expected across for the foreseeable future, with the best coverage expected in the NC mountains each afternoon this week. A couple of strong to severe storms are possible each afternoon, with damaging winds the primary hazard.

DISCUSSION

Key message 1: Hot and humid conditions remain in place for most of the week, mainly east of the North Carolina Mountains. 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 synoptic setup will remain largely unchanged the next several days, with a stalled cold front well to our north over the Midwest/Ohio Valley, and a warm, moist air mass in place across the Southeast. Subtropical ridging aloft will act as a weak block preventing any well-defined upper-level features from reaching us. So, the name of the game will be heat and humidity, as a steady influx of Gulf moisture pushes into the Carolinas.

The temperature trend nonetheless looks to provide a bit of relief through the middle of this week, with highs only in the low- to mid-90s through mid week, and heat index values only in the low triple digits along I-77 and parts of the southern Upstate, and even lower elsewhere. In particular, Wednesday and Thursday would look to be more tolerable in the wake of a weak, ill-defined cold frontal passage that should at least briefly reduce both temperatures and dewpoints. Do not currently anticipate needing any heat advisories through at least Thursday.

Toward the end of the week, as the Bermuda high begins to build strength over the western Atlantic again, heat and humidity will again increase. We'll likely be looking at mid-90s and widespread triple digit heat index values again going into next weekend.

Key message 2: Daily showers and thunderstorms are expected across for the foreseeable future, with the best coverage expected in the NC mountains each afternoon this week. A couple of strong to severe storms are possible each afternoon, with damaging winds the primary hazard.

Scattered convection continues into the evening over NC, with isolated coverage over NE GA and the Upstate. A few strong or even severe storms are possible over NC before convection weakens with loss of heating.

Deep shear may increase modestly on Tuesday as a decaying frontal boundary sags into the Tennessee Valley and approaches the area from the northwest, but in the absence of any strong forcing mechanism, coverage will be in question. Recent CAM cycles struggle to eek out some convection along I-40 Tuesday afternoon, and again a couple of strong to severe cells can't be ruled out. But confidence is limited. SPC's Marginal for the I-40 corridor tomorrow looks reasonable, at least for now.

The pattern looks to become a tad bit more dynamic through the end of the week, with a couple of shortwaves passing near or over the forecast area as the subtropical ridge retreats eastward. This opens the door for a more strongly-forced convective event, though details are unclear at this time. Things should culminate with a cold frontal passage Saturday night, when long-range ensembles agree we'll get a real air mass change. Behind the front, temperatures will cool and dewpoints will drop, but diurnal showers and storms still look like they'll continue.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Scattered convection remains over NC with isolated convection over SC and NE GA. This convection will linger into the evening, so have TEMPOs for KAVL and KHKY and PROB30 for KCLT. Just VCSH for the SC sites for now. Can't rule out some convection lingering longer near KCLT, but that's more uncertain. Expect mountain valley fog/stratus at KAVL overnight and have IFR for that. Fog also possible at KHKY. Just have MVFR for now, but IFR is possible. Convection expected again during the afternoon, but chance much better at the NC sites. Have PROB30s there, but a later start at KCLT. WSW wind becomes light overnight. SW wind returns after daybreak for all but KAVL where NNW wind develops.

Outlook: The pattern remains unsettled the rest of the week, but confidence is low on how exactly showers and thunderstorms will unfold. 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.