textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes were made to the forecast.

The aviation forecast was updated to reflect the impending 12Z TAF issuance.

KEY MESSAGES

1. Another Heat Advisory is in effect for Saturday afternoon, covering most of northeast Georgia and the South Carolina Upstate as well as the Charlotte Metro area. Hot and humid weather continues through the weekend and the first part of next week, with triple digit heat index values likely over the low terrain each afternoon. 2. There is a Slight Risk (level 2 of 5) of Severe Weather for most of the forecast area on Saturday afternoon. Scattered diurnal showers and storms develop each afternoon through the first part of next week. A couple of strong to severe storms, as well as isolated nuisance flooding, will be possible each day.

DISCUSSION

Key message 1: Another Heat Advisory is in effect for Saturday afternoon, covering most of northeast Georgia and the South Carolina Upstate as well as the Charlotte Metro area. Hot and humid weather continues through the weekend and the first part of next week, with triple digit heat index values likely over the low terrain each afternoon.

The forecast for this weekend and the early part of next week remains mostly the same. Recent water vapor imagery and UA analysis suggest the core of a stout h50 anticyclone has migrated slightly northward, and is now centered over inland Louisiana and Mississippi. Impacts for the Carolinas remain much the same, however, with anomalously warm temperatures and an influx of higher dewpoints across the area, and progged to remain through at least Tuesday, likely longer. Each afternoon will feature high temperatures in the mid- to upper-90s, dewpoints in the mid- to upper-70s, and heat index values in the triple digits across the low terrain.

A Heat Advisory has been issued for most of the SC Upstate and northern Georgia (excluding only the mountainous terrain near the NC state line) as well as the Charlotte Metro area, valid 11 AM thru 8 PM Saturday.

The signal is getting stronger for a pattern change late next week, with the majority of long-range ensembles featuring a weakness developing in the subtropical ridge, concurrent with a weak backdoor cold front finally ushering in a cooler air mass. Whether this will constitute a true air mass change, or behave more like a brief CAD-like setup, remains to be seen.

Key message 2: There is a Slight Risk (level 2 of 5) of Severe Weather for most of the forecast area on Saturday afternoon. Scattered diurnal showers and storms develop each afternoon through the first part of next week. A couple of strong to severe storms, as well as isolated nuisance flooding, will be possible each day.

Currently seeing a weak frontal boundary extending from central Kentucky into the Virginia Piedmont. Model guidance is in good agreement that this boundary will settle into North Carolina through Saturday afternoon, possibly approaching the I-40 corridor this afternoon, more or less concurrent with peak heating. Synoptic forcing will be lacking, but the front itself, though weak, could serve as a triggering mechanism for afternoon convection. Hi-res guidance remains split on coverage, likely due to how poorly-defined any boundary across our area will be. However, the parameter space for any developing storm will be impressive, featuring some 2500-3000 J/kg sbCAPE, a very deep unstable layer, and DCAPE on the order of 800-1000 J/kg. This should support at least a few severe storms this afternoon and evening, with damaging wind being the primary threat.

The next few days will feature a more typical summertime pattern, with no boundary to speak of, only a hot, muggy, pea-soup atmosphere. We can expect scattered afternoon showers and storms each day through at least Tuesday. Thereafter, a pattern change could result in decreased thunderstorm potential the second half of the week. However, the details of what this pattern change will entail are a little fuzzy at this time range, so confidence remains low on impacts.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Valley fog has developed across most of the NC mountain valleys as expected, though it hasn't quite reached KAVL yet. Mostly VFR conditions expected today, with generally FEW/SKC until a cu field breaks out by early afternoon. A round of scattered showers and thunderstorms will develop across most of the area Saturday afternoon, but will diminish after sunset, giving way to another mostly-VFR night. Another round of valley fog is likely before dawn Sunday. Light W/NW winds expected to persist through the period, except in the vicinity of thunderstorms, where they will be gusty and erratic.

Outlook: Scattered showers and thunderstorms possible each afternoon with flight restrictions possible for low stratus and fog each morning, especially in the mountain valleys.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for GAZ018-026-028-029. NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ070>072-082. SC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for SCZ008>014-019-104>109.