textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A slight increase in the rain probabilities south of I-85 mainly tonight and through tomorrow.

A small chance of rain/snow showers was added to the TN border of the northern mountain counties Friday evening.

KEY MESSAGES

1. Warmer with increasing precipitation chances starting today and lingering through Wednesday night. Snow possible at higher elevations overnight tonight, with little accumulations expected. Flurries can't be ruled out across portions of the region late Wednesday into the pre-dawn hours Thursday. 2. Some snow showers are possible at high elevations near the TN border Friday afternoon and evening as a reinforcing cold front moves through, which could result in some travel impacts Friday night. Otherwise, temperatures return to seasonal averages through the weekend and finally climb above normal early next week.

DISCUSSION

Key message 1: Warmer with increasing precipitation chances starting today and lingering through Wednesday night. Snow possible at higher elevations overnight tonight, with little accumulations expected. Flurries can't be ruled out across portions of the region late Wednesday into the pre-dawn hours Thursday.

Cloud cover continues to increase in coverage across the area an upper trough digs across the Central CONUS, while an attendant frontal boundary is currently shifting across the mid/lower MS Valley and Southern Plains. Increase in moisture continues as well with low-level southwesterly return flow as a surface high sets up shop just off the Florida Atlantic Coast and the backing flow in response to encroaching frontal system. Despite an increase in cloud cover, temperatures should manage to reach just below or near-normal temperatures as the axis of QPF response in association with the frontal boundary encroaches the NC/TN border late this afternoon. With increasing low-level moisture ahead of the front and upper-level divergence present with the leeside jet streak of the trough, expect for the forcing and moisture to line up nicely leading to scattered precip across the CWFA overnight tonight, with the better QPF amounts in the southwest upslope regions in the mountains. Temperatures are forecast to be cold enough for snow at elevations above 3500', but only minor accumulations are expected. Overnight lows elsewhere will be 4-8 degrees above-normal ahead of the boundary and slightly cooler behind the front as dry advection helps to lower temperatures and dewpoints.

The trough digs and sharpens across the Southern Plains as it takes on a positive tilt in response to a developing Rex Blocking Pattern over the Western CONUS. As a result, the attendant frontal boundary likely stalls across the CWFA during the day Wednesday, keeping elevated PoPs in place through most of the morning and afternoon hours, especially in locations along and south/east of the boundary. As of now, CAMs depict this region to be along and south/east of the I-85 corridor, with decent drying behind the front during the morning hours. In the midst of the trough sharpening, surface cyclogenesis will be underway as a surface low develops along the stalled boundary. In this case, additional forcing helps to reinforce shower activity in locations north/west of I-85 by the evening, especially when factoring in a vort max that stretches into the region. Afternoon highs will be near-normal along and south of the front, and a few ticks below-normal behind the front.

As the trough sharpens even more, the frontal boundary will gradually shift south and east of the region by the end of the period. Wrap around moisture behind the weak surface low as it shifts with the boundary could allow enough moisture and cold air to produce a quick shot of light snow showers across the NC mountains and I-40 corridor late Wednesday evening. Some CAMs have this activity drifting south into the CLT Metro and even into parts of the Upstate, mainly along and east of I-26 before slowly dissipating overnight Wednesday. Not expecting much in the way of accumulations as PoPs remain at slight chance for this possibility, but showcases the cooler temperatures and drier air filtering in behind the frontal system as overnight lows will be at or slightly below normal.

Key message 2: Some snow showers are possible at high elevations near the TN border Friday afternoon and evening as a reinforcing cold front moves through, which could result in some travel impacts Friday night. Otherwise, temperatures return to seasonal averages through the weekend and finally climb above normal early next week.

Model guidance continues to show a clipper low dropping down across the Great Lakes to Mid-Atlantic coast Thursday night and Friday, maintaining a deep northwesterly flow across the region into Saturday. Behind a reinforcing cold front, the model guidance is in good agreement showing some low level moisture dropping down and moving upslope along the TN border, though the deeper moisture moves past to the north. Will bump up the precip probs to the chance range over the nrn mountains along the TN border on Friday evening to account for this. The chances should end by daybreak Saturday, and the potential for Advisory-level snow accum appears low.

The remainder of the forecast was kept dry. The blocking pattern over the Atlantic shows signs of finally relenting next week, so a slow return to normal temps is expected early in the week, and possibly more like five degrees above normal by mid-week.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: An increase in high clouds will continue as the next frontal boundary approaches the region. Cigs will lower through the afternoon and evening as moisture increases. Expect the first instances of precipitation to reach KAVL by 00Z or so before the precipitation scatters in coverage as it travels outside the mountains. MVFR cigs/vsbys are likely to be associated around the onset of rainfall. Placed a prevailing -RA at KAVL for a three hour window with the initial bout of precip starting at 00z. Expect precip chances to spread at the rest of the terminals overnight tonight and have taken care of it mostly with a PROB30/TEMPO with associated restrictions. Cigs are expected to deteriorate quickly once the precip becomes fully established at all TAF sites with IFR to LIFR cigs and MVFR to IFR vsbys by daybreak Wednesday. Lingering precip expected during the day Wednesday, with the best chance at KCLT (prevailing line for -RA through 00z Thursday) and then the Upstate sites (PROB30 for -RA through 18z Wednesday). KAVL and KHKY likely remain on the drier side of things until the Wednesday afternoon once precip redevelops. However, the restrictions remain in place, especially for LIFR cigs through the end of the 18Z forecast period. Winds remain light through the forecast period, with generally a south to southwesterly direction through the overnight period. Winds will start to take on a northeasterly component by the end of the period, depending on the placement of the frontal boundary.

Outlook: Restrictions remain possible through Wednesday night, with precip likely diminishing for a time early Wednesday before redeveloping later in the day. Dry conditions return Thursday into the weekend for most of the terminals, outside of some NW flow snow along the NC/TN border Friday night into early Saturday morning. Gusty winds develop Friday in association with a cold front and will linger across the mountains through Saturday, but will gradually taper off east of the mountains by Friday evening.

GSP WATCHES/WARNINGS/ADVISORIES

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