textproduct: Greenville-Spartanburg

SYNOPSIS

Exceptionally warm temperatures today, but cloudy and noticeably cooler conditions develop Sunday. A cold front brings showers on Monday and ushers in still colder air Tuesday. Near- normal temperatures return mid to late week.

NEAR TERM /THROUGH SUNDAY/

As of 654 PM Saturday:

Key message 2: "Backdoor" cold front reaches the area overnight tonight, bringing markedly cooler temperatures and light rain/drizzle chances Sunday.

As an upper ridge axis progresses east thru tonight, sfc high pressure will split off and strengthen as it shifts slightly southward. 925-850mb flow will turn southerly and moistening is expected, such that low clouds will expand across the area as a result of isentropic lift. There is some spread among models as to how quickly that occurs, but by daybreak a stratus layer should cover most of our CWA outside the mountains. Excepting the particularly sensitive NAMs (both 12km and 3km), QPF response is spotty with only the upglide forcing in play, and winds remaining rather light, though it is worth mentioning that most of the CAMs have some precip response east of the mtns. The upglide does continue through the daytime hours Sunday though appears to weaken as the sfc high drifts offshore. Given the pattern, think drizzle is more likely than measurable precip; development of any form of precip should promote lowering clouds and foster in-situ CAD, but the low precip response from other models places that in question, as does the sfc high being depicted as transient. Hence, left precip chance at around 20% in most non-mountain areas with areas above the Blue Ridge Escarpment mostly in the 10-15% range. Derived max temp from the max of the NBM hourlies, with insufficient evidence to go below NBM as one would have with a high-confidence CAD event. Even so, Sunday's maxes look to be around 20 degrees cooler than today's values in our eastern zones and 10-15 cooler in our far west, so it will be a noticeable difference...though actually still a few above normal across the board.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/

As of 12:45 PM EST Saturday...

Key Message #1: Gusty winds develop ahead/behind a cold front Sunday night/Monday and persist over the mountains into Tuesday. Cold wind chills develop Monday night over the NC mountains.

Gusty SW winds will develop ahead of the cold front Sunday night and gradually turn NW behind the front on Monday, with speeds increasing thru the day. The gusty winds continue across the mtns Monday night and into Tuesday, but diminish elsewhere. Winds could reach Advisory criteria above 3500 ft by Monday afternoon, so a Wind Advisory may be needed for these locations. Elsewhere, wind gusts appear to remain below Advisory criteria, however frequent gusts of 25 to 35 mph can be expected. Cold air moving in behind the front combined with the gusty winds will create wind chill values in the single digits across much of the NC mtns and below zero values at some locations above 3500 ft. Issuance of a Cold Weather Advisory is currently not anti- cipated as values less than 5 below zero will likely be limited to the highest peaks/ridges. Nonetheless, if wind chills trend any colder, an Advisory could be needed.

Key Message #2: A robust cold front will move through the area Monday afternoon with increasing rain chances and possibly a brief period of northwest flow snow over portions of the NC mountains.

An upper shortwave closes off into an upper low over the Great Lakes on Monday and lifts up and over Quebec on Tuesday. The associated upper trof axis will rotate over our area Monday night as a robust cold front moves off the coast. Guidance has backed off on moisture transport into our area with low-level winds becoming WLY a bit earlier in the day. As a result, precip chances will be highest across the mtns with a short period of chance PoP elsewhere late Monday morning. It's still looking like all but the NC/TN border counties will get no more than 0.1 inches of precip, with up to 0.25 inches along the NC/TN border region. A brief period of NW flow snow may develop Monday afternoon before the moisture dries up, however even the most favored high elevation locations will likely get less than an inch of accumulation.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

As of 12:25 PM EST Saturday...

Key Message #1: Drier conditions and temperatures gradually warming through Thursday, with temperatures cooling again by the end of the week.

Dry sfc high pressure builds over our area from the west Tuesday into Wednesday. Another cold front is expected to move through the western Carolinas late Thursday into Friday with the latest model guidance continuing to trend drier with this clipper system. In the wake of the front, temperatures will cool somewhat, with highs a few degrees below normal for most locations. In addition, the dry airmass is ex- pected to create RH values below 30 percent across much of our fcst area each afternoon. As a result, increased fire danger could develop.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: VFR at all terminals into the pre-dawn hours, with wind being light and variable, but favoring an easterly direction. In the early morning hours, another back door front will drift in from the NE as high pressure splits off and moves off the Mid-Atlantic coast. Isentropic upglide from the SW and a light SE flow of moisture will combine to develop a low cloud ceiling right over the top of the western Carolinas before daybreak. This could initially be MVFR, but the idea is that it would quickly fall down to IFR as the uplift develops over the mtns and just to the east of the Blue Ridge. It might take until later in the afternoon for this lower restriction to finally reach KCLT. There could be patches of fog and drizzle through the morning hours, but as the forcing gets stronger and the moisture gets more plentiful, all terminals should have a period of IFR/LIFR conditions from midday into the evening. Wind should be light NE, except for KCLT which will favor a light SE direction.

Outlook: Lingering restrictions expected Sunday night into Monday with CAD and/or with arrival of stronger cold front from the west. Higher rain chances Monday ahead of the cold front. Dry and VFR conditions return behind the front by late Monday, lingering through the rest of the workweek.

GSP WATCHES/WARNINGS/ADVISORIES

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