textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12Z TAF issuance.

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 upper level anticyclone will move across the region overnight and off the Carolina Coast by the end of the day. Meanwhile, a mid/upper trof will continue to amplify over the nrn Plains/upper Midwest as a strong short wave diving out of the Canadian Plains incorporates some of the upper energy lifting out from the Rockies. This will support one more seasonally hot day across the region with fcst high temps getting back up into record territory. Changes will be in progress by the time Friday gets here with the upper anticyclone well offshore and the upper trof digging sharply across the Midwest/lower OH Valley region. The amplifying pattern will drive a cold front toward the fcst area, but it probably won't get here before temps have a chance to climb well into the 80s once more. This might not be warm enough to reach records, especially over the mtns, but it will still be well above normal.

The cold front is expected to cross the region late Friday into early Saturday morning, with fairly strong winds at 850 mb. At this time, any wind gusts that would approach Advisory criteria look to be confined to the peaks above 5K feet. An Advisory is not anticipated at this time. Moisture return will be relatively poor as the Gulf is mostly closed off, but that won't stop upslope shower activity behind the front as the low level flow comes around to NW. A few snowflakes are possible at the summit of Mt Mitchell early Saturday. The latest NBM seems to slow down the front a bit and shows low level moisture lingering through the middle part of the day, which results in a small precip prob over the western Piedmont Saturday morning. Strong cold advection aloft should also play a role by making lapse rates steeper and allowing for some weak shallow buoyancy, so isolated showers will be possible. Think precip amounts will be minimal.

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 as high pressure builds in Saturday and then lingers through Monday, with temperatures forecast to be at least 10 degrees below normal. You're going to notice it...as temperatures Saturday afternoon are expected to be 20 to 25 degrees cooler than Friday. The slight delay in frontal passage all but negates the potential for an advective freeze across portions of the mountains Saturday morning. The chances for widespread frosty/localized freezing temperatures are much greater Saturday night and again Sunday night as the center of the surface high pressure and associated ridge settle over the mountains and provide for good radiational cooling. The situation looks favorable for widespread frost across the mtns, while the northern mountains have a good chance of getting down to freezing. Climatologically, this is only about a week late. Meanwhile, east of the mtns, don't be too suprised if patches of frost develop over the nrn foothills and northwest Piedmont. We often underforecast the frost potential in the first cool autumn air mass. There will be some frost potential again Sunday night.

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 /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Mountain valley and lake/river fog in place this morning causing a wide variety in conditions at KAVL/KAND. This should dissipate by 14Z with VFR into the evening with cirrus and some high based stratocu. Mountain valley, and possibly lake/river, fog returns overnight. Light and variable wind becomes S to SW this afternoon continuing into the evening.

Outlook: Mainly dry, generally VFR conditions are expected to continue thru early next week, outside of the potential for mtn valley fog and low stratus. A robust cold front could bring sct showers and associated restrictions to the mtns Friday aftn and the entire area Friday night and Saturday. Gusty winds are expected ahead of the front on Friday and behind the front Friday night/Saturday.

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.