textproduct: Greenville-Spartanburg

SYNOPSIS

Dry weather with near normal temperatures again today. High temperatures drop below normal briefly on Friday before above normal highs return this weekend into early next week. A cold front will gradually approach out of the west Friday into the weekend, bringing rain chances back to the forecast area. Drier conditions return by Monday.

NEAR TERM /THROUGH TONIGHT/

As of 643 AM EST Thursday: Cirrus continues to stream in from the west southwest at this early hour. Temps were in decent shape, but running a degree or two above the forecast owing to the thick cloud cover.

Our weather over the next 24 hours will be controlled by a classic cold air damming wedge set-up, with a building mid/upper ridge on the East Coast supporting a parent sfc high over southern Quebec, nosing down east of the Appalachians. As we work through the day, the wedge will gradually strengthen as more forcing and moisture come into play. A short wave ejecting from the upper trof over the Plains will allow for the gradual development of isentropic upglide from the S/SW at low and mid-levels during the afternoon. The end result will be a day that won't turn out quite as pleasant as the last two, with considerable high/mid clouds keeping temps about five degrees cooler than yesterday and a few degrees below normal. Model guidance has trended toward an earlier onset of light precip over a larger area. The isentropic upglide should gradually become more productive tonight as moisture arrives from the Gulf and Atlantic to the point where the mesoscale models are all on board with some light precip breaking out mainly over the area S/E of I-85 toward daybreak. Warm advection over the top of the wedge precludes anything other than light rain where precipitation develops, as seen by the prominent warm nose in forecast soundings. Fortunately, sfc temps should stay above freezing as the warm advection develops overnight and thickens the cloud cover, so no p-type problems are anticipated. Precip probs are kept in the slight chance/chance range for now owing to concerns about initial dry air, but suspect this will have to be increased a bit in later forecasts.

SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/

As of 300 AM EST Thursday...

Key Messages:

1) Dreary Weather Expected through the Short Term

2) Well Below Normal High Temperatures Expected on Friday

3) High Temperatures Trend Back Above Normal Saturday

Hybrid cold air damming will strengthen on Friday leading to dreary conditions. Both global and high-res model guidance are trending wetter, showing light precip developing early Friday morning well ahead of a cold front approaching from the west. Most locations will see temps above freezing allowing for mostly rain. However, isolated pockets of brief freezing rain may develop across the higher elevations of the Blue Ridge Escarpment at the onset of precip Friday morning before temps climb above freezing Friday afternoon. Freezing rain accums should remain light, if any. Light rain will continue through the remainder of the day thanks to the orientation of the sfc high leading to an influx of Atlantic moisture. Precip amounts will remain light so no hydro issues are expected on Friday. High temps on Friday will drop to ~7-10 degrees below normal for most locations thanks to CAD. The exception will be the southern NC mountains where highs could still end up a few degrees above normal due to less influence from CAD. Rain chances will steadily increase Friday evening into Friday night as the front progresses eastward. With cloud cover and rain expected to continue overnight, lows Friday will end up ~10-20 degrees above normal.

The cold front will remain west of the forecast area on Saturday, allowing cold air damming to linger. However, warmer temps are expected on Saturday, trending back to above normal values. A tight temperature gradient is expected to develop Saturday, typical of CAD trying to erode, with the warmest temps expected across the mountain valleys and (generally) south of I-85. Cooler temps are expected from the Blue Ridge Escarpment to I-85 where the wedge should remain the strongest. Although the front will remain west of the CWA, precip chances will continue to increase through Saturday night. Since temps will end up well above freezing, only rain is expected. Could not rule out some isolated embedded thunder at times, especially Saturday evening/night. Moderate to heavy downpours look to develop at times as well Saturday evening/night but dry antecedent conditions should help offset any major hydro concerns. Lows Saturday night will end up ~20-25 degrees above normal thanks to cloud cover and rain.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

As of 345 AM EST Thursday...

Key Messages:

1) Showers and Isolated Thunderstorms Continue through Sunday

2) Well Above Normal Temperatures Return Sunday and Linger into Early Next Week

3) Brief Drying on Monday with Rain Chances Returning Tuesday

4) Drier and Cooler Conditions Return New Year's Day for Most Locations

Active weather continues through Sunday with the cold front expected to finally track across the forecast area. This will act to keep widespread rain around through at least early Sunday evening. Bulk shear values ~40-50 kts look to accompany the front on Sunday, and with global model guidance/ensembles depicting the possibility of a few hundred J/kg of SBCAPE during peak heating, we still cannot rule out the potential for severe wx. However, confidence on Sunday's severe wx threat remains low with this still being 4 days out. Nonetheless, will continue to monitor forecast trends over the next few days. Moderate to heavy downpours should continue through Sunday which may elevate hydro concerns somewhat but overall no major flooding concerns are expected. Temps Sunday afternoon will end up well above normal, climbing into the upper 50s to mid 60s in most locations thanks to strong southerly flow ahead of the front. Rain will gradually taper off from west to east as the front pushes east of the forecast area Sunday night into early Monday morning. No major p-type issues are expected to develop Sunday night as temps will remain above freezing for most locations. Lows Sunday night will be noticeably cooler behind the front but will still end up well above normal.

Drier conditions return briefly on Monday before another cold front increases precip chances again Tuesday into Tuesday night. Mostly rain is expected on Tuesday but if moisture lingers long enough Tuesday night, a rain/snow mix may develop across the western NC mountains as temps look to drop near or below freezing. Some NW flow snow rain/snow showers may linger along the NC/TN border Wednesday morning, but confidence remains low on this for now as the latest GFS shows dry conditions by Wednesday morning while the latest Canadian and ECMWF show lingering precip. Temps will remain well above normal through Tuesday night before trending cooler New Year's Day. However, highs on New Year's Day may remain a few degrees above normal east of the mountains.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Extensive high clouds will move overhead today, but flight category should remain VFR. High pressure to the north will keep a light NE wind in place for the next 24 hours. Thick cirrus will persist into the afternoon, by which time mid-level moisture will bring in another cloud deck, followed by low clouds after sunset as moist upglide strengthens from the south and southwest. Guidance continues its trend toward more precip over a larger area by daybreak Friday, so the TAFs include the development of a low cloud ceiling falling down through MVFR after midnight. Will probably see light rain reaching KCLT after daybreak with possible IFR ceiling.

Outlook: Broad high pressure remains in place through Friday, but a moist southerly low level flow strengthens with rain chances and restrictions increasing through Friday. The moist pattern continues ahead of a cold front arriving on Sunday with showers and restrictions, maybe even a thunderstorm. Dry high pressure returns Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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