textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Guidance showing potential for dense fog along and south of I-85 tonight, but confidence remains low.

NBM trending warmer for lows Monday night and Highs Tuesday afternoon.

Latest forecast has trended towards less coverage of freezing rain in the northern North Carolina mountains and Foothills Monday into Monday night.

Trending dry for Wednesday.

KEY MESSAGES

1. Patchy fog, possibly dense, returns along and south of I-85 tonight. Dry and warm on Sunday. 2. Cold air damming develops early next week, bringing much cooler and well below normal high temperatures as well as the potential for freezing rain across portions of the northern North Carolina mountains 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 should return by Thursday, lingering through the weekend.

DISCUSSION

Key message 1: Patchy fog, possibly dense, returns along and south of I-85 tonight. Dry and warm on Sunday.

Low clouds continue to scatter out and should be gone soon with light winds and clear skies into the evening. Some cirrus returns overnight potentially hindering the otherwise good radiational conditions. Guidance has trended back toward patchy fog along and south of I-85 where the ground remains moist. Ensembles show there is the potential for dense fog in these locations, but confidence not high enough to include in the forecast for now. Lows will be 5 to 10 degrees above normal.

The warm air mass remains in place on Sunday. Even with increasing clouds, highs will be around 15 degrees above normal. Gusty winds return to the mountains with low end gusts possible elsewhere.

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 freezing rain across portions of the northern North Carolina mountains Monday into Monday night.

Classical Cold air damming is still on track to develop Sunday night into Monday, per the latest model guidance sources as the center of a surface high tracks over New England. The center of the surface high will push off the New England coast Monday night into early Tuesday, leading to a more in-situ wedge and residual cold pool on Tuesday. Cold air damming will lead to the return of below normal highs early next week, but lows each night will remain above normal thanks to cloud cover limiting radiational cooling. Highs on Tuesday are trending slightly warmer per the NBM which matches the latest global model guidance trends. Thus, opted to only blend in some of the NBM 50th percentile for Highs on Monday as this is when the cold air damming wedge is expected to be the strongest.

As for wintry p-types Monday into Monday night, the latest NBM is now trending towards less coverage of freezing rain in the northern North Carolina mountains and Foothills Monday into Monday night. This makes sense as the last few runs of the NBM have been trending slightly warmer regarding temperatures, which matches up with the ECMWF trends as well as the gradual warming trend of the GFS the last few cycles. It now appears that elevations above 4,000 ft will have the best chance to see freezing rain develop Monday into Monday night, with rain expected elsewhere where precipitation develops (which will be mainly western North Carolina). The latest NBM shows only a 15% to 35% chance for >0.01" of ice accumulation across portions of the Northern North Carolina mountains and along the northern Blue Ridge Escarpment. The HREF and LREF continue to show slightly higher probabilities from 25% to 50% of >0.01" of ice accumulation across these same areas. However, confidence on these higher probabilities is low with guidance generally trending warmer in regards to temperatures. Drier conditions are expected Tuesday, but some isolated precipitation may linger across portions of western North Carolina. The good news is that temperatures will be warm enough to prevent any wintry p-type issues.

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 should return by Thursday, lingering through the weekend.

Guidance is still in good agreement regarding cold air damming eroding by Wednesday afternoon as the center of the surface high will be well offshore in the northwestern Atlantic by this time. The southwestern periphery of the surface ridge will extended over the Southeast through the weekend, allowing low-level southwest flow to develop. This will allow for an influx of moisture from the gulf, allowing scattered showers (and perhaps isolated thunderstorms) to return. However, guidance has gradually been trending drier regarding Wednesday, so convection can mainly be expected Thursday into the weekend. For now, coverage looks best Friday into Saturday. Well above normal temperatures will return by Wednesday, lingering into the weekend.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

At KCLT and elsewhere: Skies have cleared for all but KCLT and should by or shortly after issuance time. VFR for all through the evening. Guidance has trended back to some fog potential overnight, with ensembles showing IFR potential for the SC sites and KCLT. For now, have gone MVFR at KCLT and KAND where chance is highest, with FEW IFR clouds to show the potential. Any restrictions should lift by 15Z, maybe earlier, with VFR for Sunday. Light and variable wind for most through the night. Low end gusty NNW at KAVL becomes light and variable by evening. Winds pick up from the SW on Sunday, NNW at KAVL.

Outlook: A strong cold air damming setup is expected Monday into Tuesday, which may bring showers and associated restrictions Monday into Tuesday. VFR conditions return Wednesday. Another cold front may bring showers and associated restrictions Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

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