textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00z TAF issuance.

KEY MESSAGES

1. Near record high temperatures continue through Friday before a strong cold front brings significantly cooler and well below normal temperatures for the weekend. Frost and freeze concerns return Saturday night and again Sunday night, mainly in the North Carolina mountains. A gradual warming trend can be expected next week. 2. The strong cold front will also bring gusty winds area-wide as well as northwest flow rain showers Friday afternoon into Saturday. Drier conditions should return by Saturday afternoon, lingering into at least the middle of next week.

DISCUSSION

Key message 1: Near record high temperatures continue through Friday before a strong cold front brings significantly cooler and well below normal temperatures for the weekend. Frost and freeze concerns return Saturday night and again Sunday night, mainly in the North Carolina mountains. A gradual warming trend can be expected next week.

Upper ridging lingers over the Southeast through tonight as a positively tilted upper trough digs across the central United States. This will keep near record highs around today and well above normal lows around tonight. Although the ridge gets shunted eastward as the upper trough approaches the eastern United States on Friday, well above normal highs will return for one last day as warm advection develops ahead of an approaching cold front. KAVL is least likely to see near record highs return again on Friday but KGSP and KCLT may end up near (or may even tie or exceed) their record highs for Friday.

The upper trough tracks over the region Friday night into late Saturday, dragging a potent cold front across the Carolinas and northeast Georgia Friday afternoon into Friday evening. This will be the strongest and most impressive airmass change we have seen so far this fall with highs on Saturday expected to be around 20-25 degrees cooler compared to highs on Friday. Highs over the weekend will end up around 10 degrees below normal. The main change from the previous forecast is that NBM is trending cooler for lows each night starting Friday night. Thus, frost and freeze concerns continue to increase over the weekend as clear skies return behind the front and as the pressure gradient relaxes (especially over the mountains). Most locations in the North Carolina mountains should see frost concerns return on both Saturday night and Sunday night, with a freeze looking more likely and more widespread Saturday night. For now freeze concerns Sunday night look to be confined to the higher elevations. Frost and freeze should not be of concern Friday night with cloud cover and gusty winds expected in association with the front (see Key Message 2 for more information).

Another upper ridge will attempt to build back over the Southeast Sunday into early Monday but may get shunted just to the south and west the rest of the forecast period as an upper low develops off the East Coast. This will allow for a gradual warming trend through the workweek, with above normal highs returning by mid-week.

Key message 2: The strong cold front will also bring gusty winds area-wide as well as northwest flow rain showers Friday afternoon into Saturday. Drier conditions should return by Saturday afternoon, lingering into at least the middle of next week.

Breezy WSW/SW winds will develop ahead of the front on Friday, turning NW/N behind the front while becoming gusty Friday evening into Saturday. Gusts look to peak overnight Friday into early Saturday morning for most locations but areas along/near the I-77 corridor should see gusts peak Saturday from mid-morning to early evening. With advisory level gusts looking to remain mostly confined to elevations of 4,000+ ft, a Wind Advisory continues to look unlikely as this time due to the isolated nature of >45 mph gusts. Gusts will gradually diminish across the mountains Saturday night as the pressure gradient relaxes. Gusts will remain elevated east of the mountains through at least Sunday, possibly lingering into Monday. Gusts Sunday into Monday east of the mountains will be much lower compared to Friday/Saturday, ranging from 20-25 mph.

The cold front will also bring northwest flow rain showers to mainly the NC/TN border Friday afternoon into Saturday morning. However, some of the 12Z CAMs and global models continue to show the potential for some showers surviving east of the mountains along the frontal boundary Friday evening into early Saturday. NBM agrees with this, depicting chance PoPs across the North Carolina Piedmont and foothills as well as the eastern South Carolina Upstate. With cold air advection chasing the moisture, all liquid precipitation looks most likely, although we cannot entirely rule out some brief snow flurries above 5,000 ft.

Surface high pressure builds into the region behind the departing cold front by Saturday afternoon, lingering through at least the middle of next week. This will allow for the return of dry conditions.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Outside of another round of mtn valley fog/ low stratus overnight and into the morning, I expect dry, VFR con- ditions to continue thru the 00z TAF period. I have prevailing MVFR restrictions at KAVL beginning overnight, with a TEMPO for IFR/LIFR restrictions from 08 to 12z. Lower restrictions are possible, but confidence remains too low to go more pessimistic. Restrictions at KAVL should dissipate by roughly 14z tomorrow morning. Winds will continue to favor a SLY to SWLY direction thru the morning with some sites going light and VRB to calm at times. SWLY winds strengthen later tomorrow morning/afternoon ahead of a robust cold front. Most sites are expected to see gusts in the 20 to 25 kt range begin by the early afternoon and continue thru the evening.

Outlook: Winds turn NW/N and remain gusty behind a strong cold front Friday night into Saturday. Gusts will remain elevated thru Saturday before gradually diminishing over the mtns Saturday night. Low-end gusts will likely linger thru at least Sunday east of the mtns. The front will also bring NW flow rain showers to the NC/TN border Friday afternoon thru late Saturday morning. Some showers may spread east of the mtns, but confidence remains low on whether any of these showers would directly impact any TAF sites besides KAVL. Drier conditions return Saturday afternoon and linger thru the middle of next week.

CLIMATE

RECORDS FOR 10-15

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 86 1897 52 2002 60 2017 27 1907 1970 1928 KCLT 88 1985 53 2009 66 1985 30 2006 KGSP 86 1985 53 2002 65 1985 31 1907 1941 1970

RECORDS FOR 10-16

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 87 1897 49 1954 63 1928 29 1939 KCLT 87 1925 58 1937 68 1947 35 1939 1925 KGSP 85 1935 53 1937 67 1925 32 1907 1911 1892

GSP WATCHES/WARNINGS/ADVISORIES

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