textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated discussion for 12z TAFs.

KEY MESSAGES

1. Mainly diurnal convection is forecast through the weekend, with isolated severe storms possible. 2. Hot and humid conditions continue through the weekend.

DISCUSSION

Key message 1: Mainly diurnal convection is forecast through the weekend, with isolated severe storms possible.

A series of shortwave troughs will track thru the Upper Midwest and Great Lakes, gradually breaking down upper ridging over the Appalachians and Ohio Valley. The resulting deep-layer westerly flow will keep elevated low-level thicknesses and above-normal temps across the area thru the weekend. Muggy conditions and strong heating today will allow for fairly strong instability this aftn, with up to 2500 J/kg of sbCAPE. Deep-layer shear will remain weak, but may be enough to support a few strong to severe storms, mainly in the mtns and NC Piedmont. Damaging wind will be the main threat, as storms could loosely cluster along outflow boundaries. Convection may track into the Piedmont this evening, but guidance remains mixed on how much lingers past sunset. Overall, trends seem to be down slightly on the latest CAMs on coverage and intensity compared to yesterday's runs.

A weak front pushes into the area tonight, and stalls on Saturday. Then another cold front approaches from the west on Sunday. This should keep decent diurnal convective chances around thru the weekend. Sunday may see the highest chances over the next few days, as a more pronounced shortwave and attendant cold front crosses the forecast area. A few severe storms, with damaging winds being the primary threat, can be expected both days.

The medium range guidance generally agrees on a broad longwave trough setting up across the eastern CONUS Monday thru Wednesday, but disagree on how far south a frontal zone will push and allow dry air to spread in from the north. The 00z ECMWF and Canadian show more drying than the GFS. Either way, temperatures will trend down to slightly below normal thru midweek, and convection should remain largely diurnal and pulse mode.

Key message 2: Hot and humid conditions continue through the weekend.

Under the influence of an upper ridge, conditions are expected to be quite hot through the weekend, with temps close to 10 deg above normal today and 5-8 deg above normal Saturday and Sunday. With the axis of the ridge overhead, today is expected to be the hottest day, with highs in the mid 90s across the Piedmont, and lower 90s in the mountain valleys. Dewpts may mix out into the upper 60s this aftn, but max heat indices of 98-102 across most of the lower elevations. A Heat Advisory remains in effect for Charlotte and areas south and east, where heat indices will approach 105.

The ridge will begin to flatten with a series of shortwaves tracking thru the Ohio Valley to the Mid-Atlantic over the weekend. Saturday is expected to be a little "cooler," but still above normal, with some potential for near-Heat Advisory criteria being met across the Lakelands, especially Saturday afternoon. Temps may warm slightly again Sunday in advance of approaching frontal zone, with again some potential for near-Heat Advisory criteria. Temperatures begin a cooling trend at the beginning of the new work week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Other than some fog around KAVL until about 13z, VFR conditions expected at the TAF sites today. Winds will pick up out of the SW, generally 5-10 kt, with a few low-end gusts to around 15-16 kt possible at the Upstate sites this aftn. Isolated to scattered TSRA expected to develop across the mountains late aftn/early evening, with some tracking east/southeast into the NC Piedmont thru the evening. Still expected highest coverage over NC sites. So will continue with PROB30 for some TS at the NC TAF sites (guidance continues to trend later with convection this evening). Convection in the Upstate looks very isolated, so only VCSH at KGSP and KGMU for early evening. Winds may be variable around convection this evening, then favoring a NW direction mid to late evening into tonight, as a weak cold front crosses the area. With light moist N flow up the valley, could see fog and/or low stratus at KAVL late tonight. Confidence on any restrictions elsewhere is low at this time.

Outlook: Diurnal convection and associated restrictions are expected into early next week. Valley fog and low stratus is possible each morning, primarily in the mountain valleys.

CLIMATE

RECORDS FOR 06-12

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 91 2016 61 1903 69 1981 40 1988 1894 1964 1972 KCLT 98 1956 64 1913 74 1998 45 1972 1926 1986 1902 1943 KGSP 99 1914 61 1913 74 1981 47 1972 1920

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Heat Advisory from 11 AM this morning to 8 PM EDT this evening for NCZ071-072-082. SC...None.