textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

There is increasing potential for a light wintry precip event across the high elevations of the NC mountains Thursday morning.

In the wake of the cold front early Monday, temperatures are trending colder for the first half of next week.

Updated for new Aviation Discussion.

KEY MESSAGES

1. Record high temperatures and gusty southwesterly winds today. 2. A strong cold front arrives tonight into Thursday morning bringing widespread showers and thunderstorms, with a very low-end severe weather threat. A brief transition to a wintry mix is expected across the mountains Thursday morning, with light accumulations possible across the higher elevations. 3. Cooler and drier conditions will spread over the region late Thursday and linger thru Saturday. Another cold front arrives Sunday into Monday. 4. Colder and drier weather returns for the early part of next week.

DISCUSSION

Key message 1: Record high temperatures and gusty southwesterly winds today.

The axis of an upper ridge will continue to progress off the East Coast this morning, with deep SW flow becoming established across our area downstream of large scale height falls spreading east of the Miss Valley. Compressional warming in advance of approaching frontal zone will result in another day of very warm conditions, with record highs expected to be at least tied at the three major climate site...with mostly mid-80s anticipated east of the mountains, and around 80 in the mountain valleys. Gusty SW winds will develop this afternoon in unsheltered areas, with gusts of 25-30 mph expected across the Piedmont and foothills, and 30 to 40 mph across exposed higher mountain ridges. The very warm and gusty conditions will continue into the evening...albeit with some weakening of the winds, as pressure gradient remains tight in advance of the front.

Key message 2: A strong cold front arrives tonight into Thursday morning bringing widespread showers and thunderstorms, with a very low-end severe weather threat. A brief transition to a wintry mix is expected across the mountains Thursday morning, with light accumulations possible across the higher elevations.

A well-forced cold frontal zone will begin pushing into the southern Appalachians as early as late Wed evening, with said forcing interacting with a narrow ribbon of weak instability (250-500 J/kg of surface-based CAPE) to support a band of showers and embedded isolated thunderstorms across the forecast area from the overnight period through Thu morning. Deep layer wind shear within the frontal circulation of around 70 kts will be more than adequate for organized convective structures, with boundary-parallel shear supporting low-topped linear convective segments. Again, boundary-parallel low level shear...with 0-1 km shear magnitude of around 25 kts are not especially conducive to severe convection, but are nevertheless adequate for an isolated severe wind gust or two...and an isolated, weak tornado cannot be ruled out. Otherwise, categorical PoPs are forecast in all areas tonight into early Thu, with storm total rainfall expected to be mainly in the 0.25-0.5" range, with locally higher amounts possible associated with heavier rain showers or thunderstorms.

The cold front is expected to have a bit of an anafront character, and indeed strong cold advection is forecast to surge into the mountains Thu morning before the forcing and moisture progress east. This is expected to allow for a brief wintry mix, mainly in the higher elevations, where some light accums are looking increasingly likely...mainly above 4000 feet across the Balsams, Smokies and vicinity. and above 3000 feet across the northern mountains. At this time, confidence in the need for a Winter Wx Advisory is low, but the eventual need for one cannot be ruled out. The strong cold advection will quickly spread east of the mountains late Thu morning, and max temps Thursday are expected to be below normal in most locations...actually 10 or more degrees below normal in the mountains.

Key message 3: Cooler and drier conditions will spread over the region late Thursday and linger thru Saturday. Another cold front arrives Sunday into Monday.

A post-frontal regime is expected following the fropa Thursday morning. By the afternoon, robust CAA will be spreading across our area with much cooler and drier air. Temperatures will be noticeably cooler with afternoon highs roughly 20 to 30 degrees cooler than those on Wednesday. Overnight lows early Friday are expected to be 5 to 10 degrees below normal with widespread 30s across the area and below freezing temperatures in the mtns.

The dry weather will linger thru Saturday as a transient sfc high quickly moves over the region late Thursday and off the Carolina Coast on Friday. This will allow for SLY/SWLY return flow to pick back up over the area with temperatures warming considerably over the mtns on Friday afternoon. A weak backdoor front approaches the region Friday, with an uptick in wind gusts (especially over the mtns), the main impact for our area. On Saturday, warm frontal activation will allow for continued warming as weak SWLY low-lvl flow persists into Sunday. This should allow for an uptick in PoPs by Sunday afternoon as the environment will be more conducive to convective development ahead of the next cold front. Rapid cyclo- genesis will occur in the lee of the Rockies on Sunday as a low pressure system moves across the lower Midwest and then over the Lower Great Lakes Sunday night into Monday. The attendant cold front will approach our region late Sunday and quickly move thru early Monday. Although there appears to be ample upper lvl support/ forcing associated with this front, a lack of instability over our area when it pushes thru could make it difficult for any strong and/or organized convection to materialize. At present, most of the model guidance has it moving thru early Monday, which would likely result in minimal amounts of instability. We can expect gusty winds across our area on Monday as the front moves thru and in its wake.

Key message 4: Colder and drier weather returns for the early part of next week.

In the wake of the frontal passage on Monday, another cold snap is expected for the first half of next week. Broad/deep upper trofing will likely persist over the eastern CONUS thru the middle of the week. At the same time, robust sfc high pressure will migrate SE from Canada and spread over much of the eastern CONUS. This will create dry conditions with temperatures well-below climatology from Monday evening thru at least Wednesday.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR conditions will persist through at least this evening, with clouds generally limited to increasing high clouds. The main issue will be increasing winds, as SW winds of 5-10 kts early this morning increase to 10-15 kts and become gusty by late morning. Gusts of 25-30 kts are possible across the Piedmont and foothills this afternoon, with sheltering effects limiting the gusts to 15-20 kts at KAVL. Winds will relent somewhat during the evening, but gusts of around 20 kts will remain possible at most sites through tonight, as pressure gradient remains tight in advance of approaching cold front. This front may bring showers to KAVL late in the period, but most impacts will occur after 06Z Thursday.

Outlook: Rain showers/embedded isolated TS and associated restrictions develop late Wednesday night into early Thursday as the front sweeps across the area. Winds turn to the NW and and remain gusty Thursday, especially across the mountains. Dry conditions return late Thursday into Saturday. Another cold front may bring showers and associated restrictions Sunday.

CLIMATE

RECORDS FOR 03-11

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 79 1967 29 1924 55 2016 14 1934 1925 KCLT 83 2015 37 1960 60 1986 22 1969 2009 1934 1990 KGSP 84 2009 34 1960 60 1986 17 1969

GSP WATCHES/WARNINGS/ADVISORIES

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