KGSP issues Area Forecast Discussion (AFD) valid 2019-12-10T17:40:00Z 206 FXUS62 KGSP 101740 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1240 PM EST Tue Dec 10 2019 .SYNOPSIS... Cloudy conditions and occasional rain will persist until a cold front passes east of the region early Wednesday. Rain is forecast to briefly change to a light wintry mix before ending across the North Carolina mountains early Wednesday. Dry but cold high pressure will settle in behind the front for mid-week. Another round of brief wintry weather is possible early Friday as a coastal storm brings another round of moisture, but the bulk of this precipitation should fall as a cold rain. && .NEAR TERM /THROUGH TONIGHT/... As of 1240 PM: The cold front is crossing the area at this time bringing gusty and shifting winds. The front is also bringing a return of more widespread showers. Expect precip to increase through the afternoon with gusty W to NW winds developing. Colder air has yet to move into the mountains but should begin later this afternoon. Temps will remain warm if not increase elsewhere. No changes to the expected wintry mix for this update. Precip will continue to spread into the area from the west this morning as low-level convergence advects in ahead of the front. The flow will be oriented for upslope enhancement into the SW-facing ridges of the western mtns. PoPs will expand eastward thru the morning, with the precip shield possibly breaking up a bit due to downsloping as the near-sfc cold advection reaches the foothills, around midday. Said CAA will erode whatever's left of the wedge at that point, leading to lifting ceilings and improving vsbys. Temps will continue to be a very tricky fcst thru today, but almost all guidance (even the NAM and its usual strong preference for wedging) depicts temps getting near 70 in the lower Piedmont, and even the northern foothills rising to near 60 in spots. PoPs overall will peak in the late evening with the best combination of deep frontogenesis and upper divergence/DPVA. Temps will fall enough to support a p-type transition in the highest elevations near the Tenn border around sunset. The frontal zone is wide and characteristic of an anafront; accordingly the cooling is relatively slow aloft. Whereas we might normally expect a quick transition to snow, vertical profiles suggest a period of mixed precip before the onset of snow. The NAM's depicted warm nose is the strongest of the available guidance; the preference for this fcst was a blend of the GFS and EC, which results in mainly sleet for the first few hrs. A few areas of the northern mountains cool fast enough at the sfc to still receive a few hundredths of an inch of FZRA at the beginning of the event this evening. Given the warm ground, this likely will only be on elevated surfaces, and widespread travel issues are not expected due to icing. The anafront also features relatively light post-frontal winds in the upslope zone, which will keep accumulations small. Overall the most favored slopes are expected to see 1 to 1.5 inches, with less than an inch in most populated areas of the border counties. We will advertise the minor travel risk in the HWO and also issue a Special Weather Statement. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... As of 240 am Tuesday: NW winds advecting drier air into the forecast area Wed morning will bring a rather abrupt end to clouds and precip chances, with mostly sunny/partly cloudy skies expected by mid-afternoon. Temps are still forecast to be on the cool side, peaking at about 5 degrees below climo in most areas. The remainder of the short term will see a continuation of these dry and cool conditions. And in fact, Thu is forecast to be several degrees cooler than Wed, with increasing clouds expected by the end of the day. s of 300 am Tuesday: A dampening short wave trough will eject from the southern Great Plains late Thursday, with additional bouts of height falls expected to follow throughout the weekend. This first wave is expected to be responsible for Gulf Coast cyclogenesis Thu night and Friday. Although timing differences remain among global model guidance, they are converging toward a consensus in developing a classic Miller A cyclone across the Southeast coastal states early in the period, and this is expected to bring the next round of precipitation to our forecast area. It's looking more likely that there will be at least a transient period of wintry weather somewhere in the area late Thu night into Friday, as 1040-ish mb surface high pressure over the northern Mid-Atlantic and southern New England will support a cool/dry (i.e., low wet bulb) thermodynamic environment across the region. Guidance is in quite good agreement that moisture and forcing will overspread the forecast area from the south by daybreak Friday, and wet bulb effects should result in temps cooling to near or below freezing, with any rain falling as the freezing variety where temps do cool to the freezing mark. This will be most likely along/north of the I-40 corridor in the Piedmont and foothills, and across the eastern escarpment of the North Carolina's Blue Ridge. In terms of cold air maintenance/longevity: although the strong nature of the surface high is somewhat disconcerting, it it also quite transient, and is forecast to be somewhere in the neighborhood of Nova Scotia by 12Z Friday. This is not conducive to locking in sub-freezing temps, especially in light of the "self-limiting" nature of freezing rain and the fact that temps are likely to cool to near or just below freezing after the precip has set in. Thus, a fairly quick transition to a cold rain seems likely in the aforementioned areas, but it also seems likely that light ice accums will occur before temps warm back above freezing, mainly on elevated surfaces. It seems prudent to begin talking up this event a bit in hazardous weather outlook and briefing products. Categorical rain chances will otherwise be in place for the entire area through the day Friday, with temps at least 10 degrees below normal in in-situ/hybrid cold air damming regime. This also looks to be a solid rainfall event, with the current forecast calling for 1-2 inches for most locations. Drying conditions are anticipated for Fri night through early Saturday, with seasonably cool conditions expected to round out the medium range. Rain chances do increase to 20-30 percent by late Monday in anticipation of the next frontal system. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 300 am Tuesday: A dampening short wave trough will eject from the southern Great Plains late Thursday, with additional bouts of height falls expected to follow throughout the weekend. This first wave is expected to be responsible for Gulf Coast cyclogenesis Thu night and Friday. Although timing differences remain among global model guidance, they are converging toward a consensus in developing a classic Miller A cyclone across the Southeast coastal states early in the period, and this is expected to bring the next round of precipitation to our forecast area. It's looking more likely that there will be at least a transient period of wintry weather somewhere in the area late Thu night into Friday, as 1040-ish mb surface high pressure over the northern Mid-Atlantic and southern New England will support a cool/dry (i.e., low wet bulb) thermodynamic environment across the region. Guidance is in quite good agreement that moisture and forcing will overspread the forecast area from the south by daybreak Friday, and wet bulb effects should result in temps cooling to near or below freezing, with any rain falling as the freezing variety where temps do cool to the freezing mark. This will be most likely along/north of the I-40 corridor in the Piedmont and foothills, and across the eastern escarpment of the North Carolina's Blue Ridge. In terms of cold air maintenance/longevity: although the strong nature of the surface high is somewhat disconcerting, it it also quite transient, and is forecast to be somewhere in the neighborhood of Nova Scotia by 12Z Friday. This is not conducive to locking in sub-freezing temps, especially in light of the "self-limiting" nature of freezing rain and the fact that temps are likely to cool to near or just below freezing after the precip has set in. Thus, a fairly quick transition to a cold rain seems likely in the aforementioned areas, but it also seems likely that light ice accums will occur before temps warm back above freezing, mainly on elevated surfaces. It seems prudent to begin talking up this event a bit in hazardous weather outlook and briefing products. Categorical rain chances will otherwise be in place for the entire area through the day Friday, with temps at least 10 degrees below normal in in-situ/hybrid cold air damming regime. This also looks to be a solid rainfall event, with the current forecast calling for 1-2 inches for most locations. Drying conditions are anticipated for Fri night through early Saturday, with seasonably cool conditions expected to round out the medium range. Rain chances do increase to 20-30 percent by late Monday in anticipation of the next frontal system. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... At KCLT and elsewhere: Conditions have improved somewhat as wedge continues to dissipate. However, restrictions will continue as showers develop and move into the area. A cold front is crossing the area now causing gusty winds and a wind shift from SW to W then NW. KAVL has already shifted. Expect restrictions to continue into the evening before drier air moves in overnight bringing an end to precip and restrictions. Winds will drop off and become northerly but remain gusty at KAVL. KAVL may see a brief wintry mix, but do not expect any accums as better chances will be in the higher elevations. VFR expected for Wednesday as cold high pressure builds in. North to NE winds will continue through the day. Outlook: Dry and cold high pressure should keep conditions settled Wed night and Thursday, but a moist low pressure system is likely to bring back restrictions Thursday night. With cold air in place at the onset of precipitation, FZRA could result in some ice accumulation Thursday night or Friday morning. Confidence Table... 17-23Z 23-05Z 05-11Z 11-12Z KCLT High 83% High 95% Med 61% Low 55% KGSP Med 78% High 86% Med 63% High 100% KAVL High 83% High 91% Med 68% High 100% KHKY Med 61% Med 77% High 100% High 100% KGMU Med 78% High 91% Med 68% High 100% KAND High 100% High 86% High 82% High 95% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JDL NEAR TERM...RWH/08 SHORT TERM...JDL LONG TERM...JDL AVIATION...RWH