textproduct: Greenville-Spartanburg

SYNOPSIS

Below normal high temperatures stick around through next week. Dry and cold high pressure remains in control through Saturday before a cold front brings precipitation chances Sunday. Drier conditions develop briefly Monday before a low pressure system from the Gulf brings better precipitation chances Monday night and Tuesday. Dry high pressure returns Wednesday into Thursday.

NEAR TERM /THROUGH SATURDAY/

As of 100 PM EST Friday...

Key Message 1: Light winds diminish this evening as high pressure builds in.

Key Message 2: Coldest night of the season expected tonight.

Key Message 3: Continued cold and dry Saturday with temperatures well below normal.

A sprawling 1034 mb surface high centered over western Illinois continues to extend southeastward across the Mid and Lower Mississippi Valley at midday. Farther east, a lee trough is analyzed along the eastern slopes of the Appalachians. Our region remains on the eastern flank of the high, situated between the ridge axis to the west and the lee trough to the east. This setup has maintained breezy west to north winds through early afternoon. Winds will steadily weaken toward sunset as the surface trough shifts downstream and the high builds eastward, producing a relaxing pressure gradient across the Carolinas and northeast Georgia.

Tonight, the center of the high passes just north of the area, supporting favorable radiational cooling conditions. High clouds will stream overhead late, but they should have minimal impact on temperatures. Ensemble temperature guidance is in good agreement, with only a three degree spread between the NBM twenty fifth and seventy fifth percentiles for forecast lows. A cold airmass and ideal cooling conditions will set the stage for the coldest night of the season thus far.

Lows are expected to fall into the teens across the mountains and the lower to mid twenties across the Foothills and Piedmont. The table below compares each sites previously observed coldest temperature (1st column) to the deterministic forecast low temperature tonight (2nd column), and the NBM ensemble probabilities that tonight will be colder than the seasons current coldest night (3rd column).

Asheville, NC: 23F (11/11) | 22F | 100 percent Charlotte, NC: 29F (11/11) | 27F | 100 percent Hickory, NC: 26F (11/11) | 23F | 90 percent Greenville, SC: 25F (11/11) | 25F | 75 percent Anderson, SC: 26F (11/11) | 27F | 60 percent

High pressure shifts east on Saturday and moves toward the Mid Atlantic coast, but it will continue to control our weather. A weak southerly return flow develops by afternoon as warmer air begins to approach from the southwest. However, the warm advection arrives slowly, so highs on Saturday should be similar to today, mainly mid to upper 40s outside the mountains with 30s at higher elevations. Ensemble temperature spread remains small, with a two to three degree difference between the twenty fifth and seventy fifth percentiles.

For dewpoints, the forecast blends the NBM twenty fifth percentile with time-lagged HRRR guidance, which is currently handling moisture fields well. A deep mixed layer should promote downward mixing of drier air again this afternoon and Saturday.

SHORT TERM /SATURDAY NIGHT THROUGH MONDAY/

As of 11 am EST Friday:

Key message: Brief period of wintry precip remains possible in portions of the mountains and possibly NW NC Piedmont late Saturday night into Sunday morning ahead of a weak cold front.

SW flow remains progged to ramp up Saturday evening, along and downstream of approaching weak baroclinic zone. 45 kt LLJ will translate atop the cwfa after 06Z Sunday promoting stout winds at higher elevations. Light pcpn should be initially forced by the aforementioned LLJ, and the resultant diabatic cooling toward critical wet bulb temperatures will give rise to the chances for pockets of freezing rain to develop mainly in the mountains by early Sunday morning. Given the transient nature of the parent sfc hipres and overall light nature of the pcpn, by the time precip becomes more likely during the day Sunday, temps in most areas should be able to warm above freezing. With the frontolytic nature of the cold front, numerous showers Sunday morning will give way to diminishing chances in the afternoon.

Sfc ridging looks to reassert itself on Monday with a CAD regime seeming more likely to develop by the end of the day. We will be watching for the likelihood of western gulf cyclogenesis on Monday and the quick return of SW flow and moisture into the Southern Appalachians. Thicker cloudiness remains fcst to overspread the cwfa, and in concert with chilly NE sfc flow, maximum temperatures will be 8-10 Deg F below the December 1st normal.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

As of 1130 am EST Friday:

Key message 1: Precipitation redeveloping by Monday night. There remains the threat of a period of wintry weather for the NC mountains/foothills and NW NC Piedmont. Rain tapers off Tuesday afternoon, perhaps ending as a period of snow in the high mountains.

Ongoing high likelihood that the region will receive a round of briefly heavy precipitation at some point late Monday night and/or Tuesday as deepening Miller type A low affects the Southern Appalachians. Based on the 28/12Z NBM, The NC mountains northeast of the French Broad Valley, and parts of the NC Piedmont along and north of I-40 remain the locations where the better chances exist for a period of of wintry mix, with the highest p-type probability being fzra.

Dry-slot looks to punch through before 00z Wednesday bringing a fast end to widespread pcpn although cooling temps within the TN border counties will support a transition to snow showers there on the back side of the system.

Key message 2: Dry high pressure should return by late Tuesday night, with daytime temps trending milder Wed and Thu. Perhaps next round of rain will be on Friday.

Sunshine returns on Wednesday as high pressure builds atop the region with moderating return flow developing Thursday. Gulf moisture tap may return pcpn to the region on Friday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: At KCLT and elsewhere: VFR conditions are expected through the period. Northwest winds, varying between north and west, have begun to weaken early this afternoon. A few gusts of 14 to 18 kt remain possible for the first few hours of the 18Z TAF cycle, but mixing will diminish quickly between 20Z and 22Z. Sustained winds will ease to around 5 kt or less by sunset, with light and variable winds expected overnight.

Skies will remain SKC through late afternoon, followed by increasing cirrus from the west this evening. High clouds will gradually thicken overnight and into Saturday morning. A few patches of altocumulus may develop late, but coverage is expected to be too limited for mention until after daybreak Saturday.

Outlook: VFR conditions are expected Saturday night despite increasing cloud cover. Rain chances return on Sunday with potential sub VFR restrictions. A brief period of drier weather is expected Monday before another round of rain and restrictions arrives Tuesday. Dry and mainly VFR conditions should return Wednesday and Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Increased Fire Danger until 7 PM EST this evening for GAZ010- 017-018-026-028-029. NC...None. SC...None.