textproduct: Greenville-Spartanburg

SYNOPSIS

Low pressure moves northeast from the Gulf tonight and Tuesday with widespread precipitation. Behind the system, high pressure will result in chilly and dry conditions Wednesday and Thursday. Unseasonably cold and unsettled weather is expected Friday as another system brings more precipitation to the area.

NEAR TERM /THROUGH TUESDAY/

As of 1258 PM EST Monday...

Key Messages:

1) Fair and cool today as high pressure passes by.

2) Precip develops from the southwest this evening, mostly rain, but with pockets of freezing rain over the northern mountains and along/near the Blue Ridge Escarpment in North Carolina.

3) A Winter Weather Advisory has been expanded to include parts of Buncombe/Henderson/Polk/Rutherford counties, from 7 PM Monday through 10 AM Tuesday.

Fair weather prevails this afternoon and into the early evening as sfc high pressure migrates from the Great Lakes to New England. Meanwhile, the short wave seen in the water vapor imagery coming out across the srn Plains will help increase moisture return from the southwest. Precip probs have been pushed back further based on the 12Z HREF and the expectation that developing precip will have a difficult time working northeastward into the dry air across our region.

But, develop it will, as the 850mb flow improves quickly this evening, increasing the moisture flux and contributing strong isentropic lift that spreads northeast between 00Z and 06Z to engulf the entire fcst area. Thus, precip probs will be ramped up all the way to categorical SW to NE in that time frame. The slightly later start might allow for a bit more cooling down farther to the S/SW along the Escarpment, such that when the precip arrives the temps will have an easier time wet-bulbing down to around freezing. Meanwhile, strong warm advection will develop a formidable warm nose overhead. The upshot is that after some mixed precip potential at onset mainly over the mtns, we end up with an R/ZR situation. The majority of the region will have nothing but a cold rain, but the usual areas over the nrn mountains and near the Blue Ridge Escarpment from Blowing Rock down to Saluda, including the eastern-most parts of Buncombe and Henderson counties should see a period of freezing rain starting late this evening. The warm nose makes the situation elevation-dependent, so places that are above about 4000 feet or so should be mostly rain after some mix at onset. There is enough icing potential to expand the Advisory down south to include the mountain parts of Polk and Rutherford and also Henderson and Buncombe. NOTE that the ice potential will be east of a line from roughly Swannanoa to Fairview and Edneyville, with little to no accumulation expected in Asheville and Hendersonville and west of the I-26 corridor. Of course, things could go wrong. The most likely failure mode would be that colder air is more extensive which could require expansion across the NC Foothill zones, or that the cold air holds on longer and allows for some icing to approach or exceed Warning criteria. The warm advection should be strong, so precip should be all rain by around daybreak. Temps will naturally be at or below normal.

The precip will move off to the east steadily and should be over by early afternoon. Assuming we get some partial clearing and dry air in the afternoon once the sfc wave moves to the east, temps could rebound to around normal.

SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/

As of 1237 PM EST Monday:

Key Message 1: Northwest flow in the midst of ending Tuesday evening following the departing system from the Near-Term period. Most locations across the area below freezing for overnight lows Tuesday.

Ongoing northwest flow precip should fully diminish by Tuesday evening along the immediate Tennessee border as drier air disrupts the shallow layer of moisture along the favorable upslope zones. Weak surface high will move in from the northwest as CAA works into the CWFA. Gusty winds gradually subside across the mountains overnight Tuesday as the center of the surface high shifts into the OH/TN Valleys. Temperatures will be in the upper teens and 20s across the mountains with mid to upper 30s elsewhere for overnight lows with decent radiational cooling conditions outside of boundary layers struggling to fully decouple.

Key Message 2: Dry weather Wednesday and Thursday with temperatures rebounding from Wednesday to Thursday.

Weak surface high moves across the southeastern CONUS on Wednesday as low-amplitude ridging settles over the region in response to a digging upper trough over the western CONUS. A cold front is shown encroaching the CWFA from the northwest on Thursday as the front sags through the area without much fanfare as better forcing for ascent remains north and available moisture stays south over a developing baroclinic zone over the Gulf Coast region. In this case, not much change to the overall airmass. Temperatures will be cool Wednesday with afternoon highs in the 40s in the mountains and upper 40s to lowers 50s across the Piedmont. Overnight lows should run below freezing with 20s and lower 30s expected with good radiational cooling conditions in place. Weak downslope component should help bump temperatures a few degrees higher compared to Wednesday for afternoon highs on Thursday.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

As of 115 PM EST Monday:

Key message 1: Next system moves into the western Carolinas and northeast Georgia late Thursday into Friday, with wintry precipitation possible, mainly across the mountains as a result of another cold-air damming event. Confidence remains low overall for occurrence of precipitation and winter weather.

Stronger surface high (~1030mb) moves in behind the short-term cold front as it shifts from the Midwest through the OH Valley and offshore the Mid-Atlantic Thursday night through Friday. The aforementioned cold front will stall south of the CWFA, in the vicinity of the I-20 corridor. Activated baroclinic zone over the southeastern CONUS will induce Miller-A surface cyclogenesis along the boundary as it becomes reactivated and develop a low pressure system as the next storm system moves across the eastern Gulf Coast Friday and over the Carolina Coast Friday night. Latest model guidance have trended drier with a shorter period of good QPF response. The complicating factor will be the strength of the in-situ CAD as it develops Friday as the onset of precipitation Friday morning could start out with a mix bag of wintry precip in the North Carolina mountains/foothills, as well as the I-40 corridor before transitioning to all liquid for most locations. The probability of any accumulating snow or ice remains confined to the northern Blue Ridge mountains at this time, especially now with the latest trends keeping the system slightly further south, which in turn, limits the overall available moisture. However, this would limit the presence of a strong warm nose, which could lead to more of snow/sleet across the high elevations instead of a predominately freezing rain event. Still a lot of factors to consider, but the potential for another nuisance winter system across the mountains is definitely in the playing cards. Elsewhere, outside of the mountains, model solutions, including ensembles indicate mostly a cold rain. Either way, temperatures will be cold on Friday with most locations in the 30s and 40s across the CWFA, with near freezing temperatures in the mountains/foothills, where the chance for wintry precip is best.

Key message 2: Calmer weather in store for the latter half of the weekend into early next week. Slight rebound in temperatures with trends keeping values near normal.

One consensus that model guidance are picking up on is the overall end time of the weekend system as precip could linger into Saturday before shifting east of the CWFA by Saturday night as a southern stream shortwave aids in a faster storm departure. Precip chances have reflected this in the latest forecast update as trends have lowered to slight chance (15-24%) and chance (25-54%) PoPs across the area and fully drying out by early Sunday. If the latest model guidance continue with a drier trend, then the main precip timing will be Friday and Friday night with less coverage for Saturday. Weak cyclonic flow aloft remains in place through the weekend as another shortwave is shown swinging within the mean flow and approaching the area by the end of the weekend. Guidance differ on the overall QPF response, but looks light overall, even with the more aggressive solutions. Slight chance PoPs are introduced across the mountains Sunday night, but remains dry elsewhere. Temperatures continue to run within a few degrees of normal over the weekend into the early next week, but is subject to change depending on how long CAD lingers, especially for Saturday.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: VFR conditions will persist past sunset and probably thru the late evening, but clouds will thicken after sunset and ceilings will start to drop as moisture spreads quickly northeastward. Wind should be NE. The development of light precip after about 02Z from SW to NE will bring the ceiling steadily down thru MVFR and into the IFR to LIFR range at all terminals in the late night/early morning hours. By the start of operations in the morning, it should be raining at all terminals with an IFR restriction most likely. Due to the strong SW flow, there could be some LLWS across KAVL at that time. Variability between LIFR and MVFR can be expected. Precip type looks to be just a cold rain at all terminals, but will have to monitor KAVL and KHKY for possible freezing rain before daybreak. Temps warm by 13Z and that should end that threat. The system moves thru fairly quickly. Ceilings may crash to LIFR around daybreak as the precip starts to taper off. Quick improvement is expected right around the end of the period, with wind coming around to SW to W.

Outlook: VFR conditions return Tuesday night into Wednesday. Another system may bring rain and associated flight restrictions to the region on Friday and into the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Winter Weather Advisory from 7 PM this evening to 10 AM EST Tuesday for NCZ033-049-050-053-065-501-503-505-507-509. SC...None.