textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Confidence is increasing in a fog event late tonight into Saturday morning. While some dense fog is expected, the extent of any dense fog remains unclear, but a Dense Fog Advisory may eventually be needed.

Confidence on possible wintry weather Monday into Monday night across northern North Carolina remains low as this will be highly dependent on the strength of cold air damming.

KEY MESSAGES

1. A few showers lingering this afternoon, with areas of fog and locally dense fog developing tonight. Dry and much warmer Saturday through Sunday. 2. Cold air damming develops early next week, bringing much cooler and well below normal high temperatures as well as the potential for wintry weather across northern North Carolina Monday into Monday night. 3. Cold air damming should erode by Wednesday afternoon, allowing much warmer and well above normal temperatures to return the rest of the workweek. Rain chances may stick around but confidence is low.

DISCUSSION

Key message 1: A few showers lingering this afternoon, with areas of fog and locally dense fog developing tonight. Dry and much warmer Saturday through Sunday.

Inverted ridge extending from surface high progressing away from the New England coast will steadily weaken through the period, as heights fall upstream through much of the period, maintaining a long wave trough centered just west of the area. Consequently, in situ cold air damming will weaken as well, and is forecast to be a thing of the past by Saturday afternoon. In the interim, increasingly ragged and remnant frontogenetically-forced shower band ongoing across the Piedmont will move east and/or dissipate within the next 1-2 hours. Clearing and attendant very weak destabilization across the mountains could result in a shower or two there later this afternoon. Otherwise, dry conditions are expected through Sunday. Lingering, increasingly shallow low-level moisture along with weakening surface winds will yield the likelihood of areas of fog tonight into early Saturday. Dense fog is very possible on at least a localized basis...and certainly can't rule out the eventual necessity of a Dense Fog Advisory.

With clearing skies expected across much of the area by early Saturday afternoon, temperatures are forecast to soar under fairly high partial thickness values, and max temps are forecast to be around 10 degrees above climo in most locations. The warm conditions will continue into Saturday night, culminating in a very warm Sunday...where a weak downslope/compressional warming will contribute to temperatures of around 15 degrees above normal...with lower/mid 70s expected across the Piedmont, foothills, and the lower mountain valleys.

Key message 2: Cold air damming develops early next week, bringing much cooler and well below normal high temperatures as well as the potential for wintry weather across northern North Carolina Monday into Monday night.

Cold air damming gradually develops Sunday evening into Monday, as the center of surface high pressure situates itself over the northeast. Although the center of the surface high shifts offshore on Tuesday, in-situ cold air damming should remain in place through Tuesday night per the 12Z GFS. This will allow much cooler and well below normal high temperatures to return early next week. Lows will remain above normal Sunday night through Tuesday night as cloud cover will limit radiational cooling.

Depending on the strength of the cold air damming wedge, Old Man Winter may not be quite done with us yet...per the 12Z GFS anyway. The GFS continues to show a stronger cold air damming wedge compared to the ECMWF. The 06Z ECMWF is much warmer compared to the 12Z GFS, with roughly a 5-10 degree temperature difference. Thus, the ECMWF mainly depicts rain falling Monday into Monday night while the 06Z GFS shows the potential for a wintry mix developing across a good chunk of western North Carolina, outside the southwest mountains. However, confidence on this remains very low as the 12Z GFS has trending slighter cooler compared to its 06Z counterpart, leading to more widespread wintry weather across portions of western North Carolina. So, any wintry weather that develops will be highly dependent on the strength of cold air damming. Even with blending in some lower temperature guidance for highs on Monday to account for the wedge limiting daytime heating, only really ended up with a wintry mix along and north of I-40 across portions of the northern North Carolina mountains, the northern North Carolina Foothills, and the northern North Carolina Piedmont Monday afternoon and evening. Rain would be expected elsewhere across western North Carolina Monday afternoon and evening. Could see a transition to freezing rain across the northern North Carolina mountains Monday night but confidence on this remains low as cold air damming could limit how cold we get Monday night. The NBM appears to be trending slightly colder Monday night which appears to match up with the GFS trends. So, once again any wintry p-types Monday night will be highly dependent on the strength of the cold air damming wedge. Temperatures on Tuesday should end up slightly warmer, keeping any wintry p-types at bay.

Key message 3: Cold air damming should erode by Wednesday afternoon, allowing much warmer and well above normal temperatures to return the rest of the workweek. Rain chances may stick around but confidence is low.

Cold air damming should erode by Wednesday afternoon, per the 12Z GFS and 06Z ECMWF, as the center of the surface high will be well offshore in the northwestern Atlantic by this time. However, with the southwestern periphery of the surface ridge extended across the Southeast through Friday, S/SW low-level flow will pump of rich gulf moisture into the region. The erosion of cold air damming combined with the influx of gulf moisture will lead to the return of much warmer and well above normal temperatures the remainder of the workweek. This pattern will also act to keep daily rain chances around through Friday. The latest global model guidance sources are not in great agreement regarding the coverage of rain so confidence on PoPs is low Wednesday through Friday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: IFR cigs are in place across much of the Terminal Forecast Area this afternoon, although gradual improvement is occurring from the W and N. VFR conditions are expected to linger through the afternoon at KAVL, with MVFR conditions persisting (or soon developing) at KAND and KHKY. Can't rule out improvement in the IFR at KCLT...and especially at KGSP/KGMU, but this confidence is low at this point, and IFR cigs are forecast to linger there through the afternoon. With plenty of low level moisture expected to linger through tomorrow morning, cigs are expected to begin filling in and lowering across the Terminal Forecast Area this evening, with widespread LIFR cigs expected by late tonight.

In terms of visby...MVFR is forecast to linger around KCLT and vicinity through mid-afternoon, and a shower cannot be ruled out at KCLT through mid-afternoon. Visby is otherwise expected to be VFR until at least mid-evening. BR/possible FG will become widespread late tonight, with at least persistent IFR visby, and at least tempo LIFR expected at most sites. VFR visby and cigs are expected at all sites by around noon Saturday. Winds will be NE at 5-10 kts at most sites through the afternoon, weakening and becoming light/variable by late tonight.

Outlook: Fog and low stratus should clear out and VFR conditions should return by midday Saturday. Another front may bring showers and associated restrictions Monday into Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

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