textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Low temperatures have been decreased slightly Sat night and Sun night, with growing confidence of frost potential.

KEY MESSAGES

1. Seasonably dry and cool weather returns this weekend, with frost likely Saturday night and Sunday night. 2. High temperatures warm above normal again early next week before another frontal system brings small rain chances and much cooler weather late in the week.

DISCUSSION

Key message 1: Seasonably dry and cool weather returns this weekend, with frost likely Saturday night and Sunday night.

A long wave trough will continue to become established across the Eastern Seaboard through the weekend, with associated cool/dry low- level ridge forecast to gradually build over our forecast area. A return to near-normal temperatures is expected tonight and Sunday. The surface gradient is forecast to relax sufficiently for good radiational cooling conditions Saturday night and again Sunday night, when min temps are forecast at around 5 degrees below climo. This will create frost/freeze concerns for locations where the growing season is still considered to be ongoing (i.e., all areas outside the mountains.) At least Frost Advisory conditions appear likely across the I-40 corridor both nights, with lesser potential to the south and west. However, a freeze is certainly within the realm of possibility along the I-40 corridor, with some frost potential elsewhere. (Note: we will consider the growing season ended across our entire area when a freeze occurs or on 11 November, whichever occurs first.)

Key message 2: High temperatures warm above normal again early next week before another frontal system brings small rain chances and much cooler weather late in the week.

Long wave trough axis will shift off the East Coast Monday, to be displaced by a low-amplitude ridge across our region through mid- week. The low levels will remain dry, as surface high pressure is forecast to dominate over the Southeast and adjacent coastal waters. This will result in large diurnal temp ranges through mid-week, with max temps forecast to be a solid 5 degrees above normal Mon through at least Wed, while near-normal min temps are expected.

By late next week, the global models depict a very strong ridge developing across the West, with a series of short wave troughs of increasingly Arctic origin forecast to dive into the eastern half of the country by week's end. The result of this is an evolving consensus of an impressively deep trough developing across the East by Day 7. Associated strong frontal zone is currently forecast to cross our region in the Thu night/Friday time frame. In terms of PoPs, the devil is in the details, as questions abound regarding the timing/location of surface development and said surface feature's ability to tap into a moisture source. As such, the global models are a bit all over the map re: precip potential. For now, we limit PoPs to 20-30% and confine them to western NC Thu through early Fri. Regardless of how the precip scenario unfolds, much cooler weather is likely late next week, such that forecast maxes Friday are 5-10 degrees below climo.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR is forecast to prevail at the TAF sites through this cycle, as dry air gradually overtakes the region in the wake of a cold front. Northwest upslope flow interacting with moisture banked against the western slopes of the Appalachians could result in some stratocu working its way up-valley toward KAVL tonight, but any cigs will be brief. Moisture is expected to be sufficient to result in some fog/possible low stratus development in the more sheltered mountain valleys early Saturday, but winds are expected to remain too elevated for fog/low stratus formation at KAVL. Otherwise, winds will generally favor a NNE->NNW direction at 5-10 kts. The exception will be gustier winds from the NW at KAVL, where some 20-25 kts gusts will be possible from late this afternoon through Sat morning.

Outlook: VFR conditions expected this weekend into early next week. The exception will be a continued potential for morning mountain valley fog.

GSP WATCHES/WARNINGS/ADVISORIES

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