textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No major changes for snow probabilities tonight across the North Carolinas zones, with light accumulations possible through daybreak Thursday.

Confidence increasing on snow shower chances along the TN border Friday night. Confidence remains low on any amounts.

KEY MESSAGES

1. Periods of mainly light rain across the area today. There is a chance that rain could mix with or change over to snow showers across North Carolina tonight, with only spotty very light accumulations expected. 2. Snow showers are expected to develop along the TN border Friday afternoon and evening behind a cold front, which could result in some travel impacts Friday night. Very gusty winds are expected to develop across the high elevations of the NC mountains late Friday night and Saturday morning, which could result in scattered power outages. 3. Dry Saturday with borderline low afternoon RH in some places east of the mountains, which may result in increased fire danger. A warming trend is expected through the middle part of next week, with the next weather system moving in Wednesday.

DISCUSSION

Key message 1: Periods of mainly light rain across the area today. There is a chance that rain could mix with or change over to snow showers across North Carolina tonight, with only spotty very light accumulations expected.

A positively tilted upper trough will sharpen and deepen over the Ohio Valley to the Lower MS Valley today in response to a rex blocking pattern over the West Coast that intensifies. The stalled boundary over the area currently will gradually shift south and east through the evening and eventually make a full fropa overnight. Temperature/Dewpoint gradient seems to be the best indicator of the boundary's position with afternoon highs likely in the upper 40s to lower 50s along and south of I-85 where the front is being analyzed, while locations north/west of I-85 only reach into the upper 30s to lower 40s. Better moisture returns south of the boundary with the help of upper-level divergence from the overlaid jet streak has helped stream in a continuous light QPF response on the southeastern fringe of the CWFA.

As the trough deepens over the next few hours, weak cyclogenesis will help to develop a surface low along the boundary and will push through the area, which can be seen near northwest Georgia. With the additional forcing this provides, expect for precip to spread back over the region through this evening. Height falls leading to cooler thicknesses should help the precip changeover to snow on the wrap around position of the surface low tonight as it shifts south and east of the area. CAMs continue to pick up on a transition from mostly rain to snow, with very light accumulation over portions of the western Piedmont and foothills of North Carolina, as well as the North Carolina mountains. QPF will be light and the better frontogenetical forcing will be situated mainly east of the region. However, some of the soundings show some support of light freezing rain as profiles may not be saturated enough to tap into the dendritic growth layer once temperatures fall overnight. Coverage would be very spotty in this instance for freezing rain and have decided to hold off on any Advisory at this time and will likely handle any wintry weather with the current HWO mention and an SPS. Temperatures in the latest guidance have actually warmed a couple of degrees overnight tonight which makes all the difference in minor winter weather impacts and basically none in this type of setup.

The trough axis should slip east of the area by Thursday afternoon as drier air filters into the region, ending most of the precip after daybreak Thursday, but model guidance hold onto to some form of isolated precip through the late morning hours, so can't fully rule out drizzle or a flurry chance in portions of the CLT Metro and Upstate during this time before the drier air overrules any ongoing precip as it shifts south. Despite clouds scattering by the afternoon, weak CAA will keep temperatures 4-8 degrees below normal for afternoon highs, with values closer to normal in the typical downslope locations.

Key message 2: Snow showers are expected to develop along the TN border Friday afternoon and evening behind a cold front, which could result in some travel impacts Friday night. Very gusty winds are expected to develop across the high elevations of the NC mountains late Friday night and Saturday morning, which could result in scattered power outages.

Model guidance remains in good agreement concerning the passage of a reinforcing cold front late in the day on Friday, associated with a clipper low moving across the Great Lakes to New England, and off the coast Saturday. The model solutions offer more support to the idea that low level moisture behind the front will get run up the west slopes by a strengthening NW flow, resulting in shower production along the TN border beginning in the afternoon and maximizing Friday evening, though the model blend still seems to lag the trend. The precip probs will be kept in the chance range for now, but are more likely to get bumped up rather than down over the next day or two. Profiles continue to support an elevation-dependent rain/snow scenario. Precip will be fairly light and the duration fairly brief, so if anything, the new forecast accum potential drifts back away from an Advisory-level event.

The new model blend appears to strengthen the wind potential across the higher terrain Friday night and Saturday morning as the 850mb gradient tightens. Guidance shows a belt of strong winds at 850 mb intersecting the mountains after 00Z Saturday with the potential to reach Wind Advisory criteria around the 45-50% range. This will be monitored. Oddly enough, the wind doesn't appear to be strong enough to pull the wind chill down cold enough to reach Cold Weather Advisory range.

Key message 3: Dry Saturday with borderline low afternoon RH in some places east of the mountains, which may result in increased fire danger. A warming trend is expected through the middle part of next week, with the next weather system moving in Wednesday.

As we dry out behind the cold front on Saturday, the model blend suggests borderline low RH on Saturday afternoon, with a minimum of RH expected in extreme northeast GA and the western tip of SC. The guidance gives a 50/50 shot of RH falling below 30 pct, so we will be keeping an eye on the enhanced fire danger around that part of the fcst area.

Ordinarily, we might not mention the weather beyond Saturday in our new way of writing forecast discussions, but in this case the warming trend into the middle of next week is notable because of how cold it has been the past few weeks. Indications are the blocking pattern over the north Atlantic will finally break down over the weekend and allow the eastern upper trof to move away offshore, with the nrn stream retreating northward as the upper pattern flattens across much of the CONUS. The trend in the model guidance looks even warmer than earlier runs, to the point where we have temps climbing into the 10-15 degree range ABOVE normal by Tuesday and Wednesday of next week. This is going to make it feel like Spring has arrived, but it is a bit too early to give up on winter just yet. A southern stream system may move into the region on Wednesday, but temps support nothing but rain even across the NC mountains with such warm temperatures. There might even be a thunderstorm chance across parts of the region if the warm trend continues.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

At KCLT and elsewhere: Precip activity will increase in coverage through the afternoon and evening before gradually diminishing overnight tonight. Winds are beginning to turn northeasterly and will remain that way through much of the forecast period once a frontal boundary shifts south of the region over the next few hours (KAVL maintains on north-northwesterly component). An uptick in winds will be evident overnight with speeds elevating to 5-10 kts, while low-end gusts can't be ruled out. IFR/MVFR cigs and vsbys are mostly in place and will cover the entire area by 00z. Cigs should lower through the night as well with some TAF sites dipping to LIFR for a time. -RA is in the forecast for all TAF sites through the early morning hours Thursday, with a PROB30 mention for -RASN at KHKY and KCLT where cold enough air should support a brief period of the precipitation mixing and/or transitioning from rain to all snow during the pre-dawn hours. Drier air should end all precip by 12Z Thursday as cigs gradually lift and scatter by the very end of the 18Z TAF period, eventually returning to VFR at all terminals by Thursday afternoon.

Outlook: Dry and VFR conditions through the weekend. Gusty winds develop Friday in association with a cold front and linger across the mountains through Saturday, but will gradually taper off east of the mtns by Friday evening.

GSP WATCHES/WARNINGS/ADVISORIES

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