textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Mountain PoPs have increased for Fri afternoon into Fri night.

Min temperatures have decreased slightly for Sat night and Sun night.

KEY MESSAGES

1. Near record high temperatures linger through Friday before a strong cold front crosses the region Friday afternoon/evening. Gusty winds are expected across the higher elevations along and behind the front, but confidence in Advisory level wind gusts is low. 2. Behind the cold front, temperatures will drop below normal through the weekend. Low temperatures across the mountains will be cold enough for frost and could drop below freezing in some places early Sunday morning.

DISCUSSION

Key message 1: Near record high temperatures linger through Friday before a strong cold front crosses the region Friday afternoon/evening. Gusty winds are expected across the higher elevations along and behind the front, but confidence in Advisory level wind gusts is low.

An anticyclone and associated ridge will remain over the East through Thursday before progressing over the western Atlantic, as an area of strong height falls dives from the northern Great Plains Thu afternoon to the Appalachians by the end of Friday. Attendant strong cold front is forecast to move into the western part of our CWA by late Fri afternoon, then quickly sweep across the area through the evening. In the interim, very warm/near-record high temperatures are expected to continue ahead of the front, with temperatures mainly in the mid/upper 80s expected across the lower elevations Thu and Fri. Gusty SW winds will develop ahead of the front Fri afternoon across the high elevations and portions of the Piedmont.

With the anticyclone in place ahead of the front, moisture return will be minimal, and in fact, there is expected to be more moisture on the cool side of the front than in the warm sector. Therefore, PoPs for our area are expected to be maximized within developing NW/upslope flow/cold advection regime across the NC mountains Fri evening, especially for the counties bordering TN. A brief period of flurries or rime icing is possible above ~5000' before the moisture depletes Saturday morning.

Otherwise, gusty NW winds will develop across the area Friday evening, continuing through Saturday morning before tapering off during the afternoon. The forecast surface gradient will be marginally supportive of Wind Advisory-level gusts, but these are most likely to remain confined to the higher peaks and ridge tops.

Key message 2: Behind the cold front, temperatures will drop below normal through the weekend. Low temperatures across the mountains will be cold enough for frost and could drop below freezing in some places early Sunday morning.

The strong cold front is expected to bring in the first true autumn continental air mass for the weekend into early next week, with temperatures forecast to be at least 10 degrees below climo from Saturday through Monday, with temps Saturday afternoon forecast to be as much as 25 degrees cooler than Friday. An advective freeze is possible across portions of the mountains Saturday morning, but should be largely confined to the higher elevations. The larger concern for widespread frosty/localized freezing temperatures will be Sat night and again Sunday night as the center of the surface high pressure and associated ridge settle over the Appalachians and vicinity. While a widespread mountain frost appears to be the most likely scenario, there's at least a good chance that some of the high valleys of the northern NC mountains, as well as some of the more sheltered areas across the TN border counties will see their first freeze of the season on one of these nights. There will also be some potential for areas of frost to develop along the I-40 corridor outside the mtns, particularly across the northwest Piedmont, but confidence is low at this juncture.

As heights begin to rise and the surface ridge gradually weakens over the Eastern Seaboard, temperatures begin to moderate, but remain below normal Monday/Mon night, further warming to right around climo by the middle of next week. Conditions will remain dry/precip free as the air mass remains seasonably dry.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions are forecast to prevail through much of this forecast period. The only exception is at KAVL, as fog/low stratus is again expected to develop in the mountain valleys. Restrictions did not develop at KAVL this morning, but the fog/stratus was very close, and the path of least regret is to advertise some degree of restrictions (MVFR for now) developing prior to daybreak. Can't rule out restrictions developing at other TAF sites, especially those near lakes (i.e., KAND and KHKY) but confidence is low at this time. Light SW winds ate expected to develop this afternoon, becoming light/variable or calm this evening.

Outlook: Mainly VFR conditions are expected thru early next week, outside of the potential for mtn valley fog and low stratus each morning, mainly through Friday. A cold front could bring scattered showers and associated restrictions to the mountains Friday afternoon and evening. Gusty winds expected all areas ahead of the front Friday and behind the front Friday night/Saturday.

CLIMATE

RECORDS FOR 10-14

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 82 1928 51 1907 64 1954 25 1988 KCLT 87 2021 56 1922 68 1883 32 2006 1940 1881 KGSP 86 1985 57 1907 67 1954 30 1988 1928

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.