textproduct: Greenville-Spartanburg

SYNOPSIS

Dry but mild high pressure persists today. A moist cold front crosses the area Tuesday into Wednesday, producing widespread showers and a few thunderstorms. Much colder temperatures arrive behind it and continue into the weekend. Forecast confidence is very low beyond Saturday.

NEAR TERM /THROUGH TUESDAY/

As of 1217 PM EST Monday: An open shortwave trough currently located over the Central Plains will shift over the Mid-MS Valley tonight and into the Great Lakes region by Tuesday with an attendant cold front. Surface high currently parked over the Mid-Atlantic will gradually move offshore by this evening and set up shop over the western Atlantic by Tuesday. Better low-level return flow and a warm front that lifts into the area tonight into Tuesday will place the area under a warm sector regime by daybreak Tuesday, especially over the Upstate, northeast Georgia, and southern Blue Ridge Escarpment. As a better LLJ (35-45 kts) punches in from the south behind the front, expect a few warm advection showers with isentropic enhancement to develop during the early morning areas before the first band of DPVA and height falls move a blob of precip across the area from west to east after deeper convection develops over the Deep South, starting around daybreak Tuesday in the southwest mountains and Upper Savannah River Valley. Overnight lows will vary from the southwestern portion of the CWFA to the northeast in the western NC Piedmont as better cloud cover and rising dewpoints will push into locations west of the I-26 corridor during the nighttime period, which allows temperatures to be 10-15 degrees above normal, while locations east of the I-26 corridor run 5-10 degrees above normal.

After the initial blob of precip lifts northeast of the CWFA by the early afternoon, a lull in the precip may occur outside of a few WAA showers ahead of the main front encroaching the region. Widespread mid 50s to lower 60s dewpoints will allow for some form of destabilization to be present as the incoming activity develop convective elements. However, CAMs struggle to form much in the way of surface instability, but there will be 250-500 J/kg of MUCAPE. The main portion of the convection moves into the area after sunset and pushes across the CWFA through the rest of the evening and the first half of the overnight period. Deep layer shear (0-6km) of 45-55 kts, elevated instability, and good moisture available will allow a broken line of convection along the main frontal band. Still looking like the severe threat will be very low, but not nonzero, with a damaging wind gust possible in one or two storms. QPF response will be locally heavy with most guidance showing 1-3" of total rainfall, mainly being highlighted across the favorable upslope zones along the southern Blue Ridge Escarpment and southwest mountains, with less than inch elsewhere. With the CWFA placed in a robust warm sector despite cloud cover, afternoon highs will still manage to run 5-10 degrees above normal, with some locations south and east of I-85 topping out at ~15 degrees above normal where the warm sector will be established for a longer period of time.

SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/

As of 1103 AM EST Monday...

Key Messages:

1) Severe weather increasingly unlikely on Wednesday as showers/thunder exit the area early in the day.

2) Clear, dry, and cool weather returns by Wednesday night and persists into Thursday.

Still looking like we're back to a non-severe setup for Wednesday, as operational guidance doubles down on a faster frontal passage...to the extent that now, by 18z Wednesday, most models depict precipitation largely east of us, an even low-end surface-based instability barely clipping our southeastnermost zones, if at all. So...think this will largely preclude any potential for severe storms on Wednesday; rather, expect a steady NW breeze to continue through much of the day in the CAA regime that develops behind the front. Expect skies to clear up quite a bit through the day Wednesday...allowing better solar insolation alongside weak downsloping...offsetting any effects of CAA and resulting in highs actually a degree or two warmer than on Tuesday.

By Wednesday night, however, as winds weaken, downsloping abates, and decent radiative cooling takes hold...expect lows in the mid-30s, possibly hitting freezing across some Foothills locations outside the thermal belt. Considerably cooler weather is in store for Thursday, as the colder postfrontal air mass fully settles into the area...resulting in highs only reaching the lower 50s across the low terrain.

LONG TERM /THURSDAY NIGHT THROUGH MONDAY/

As of 1137 AM EST Monday...

Key Messages:

1) Bitterly cold air remains in place through at least Saturday.

2) Another cold front arrives on Sunday or Monday, bringing mostly rain but the possibility of frozen p-types to the mountains.

A cold air mass will remain in place across the region through at least Saturday. Highs on Friday and Saturday may not climb out of the 40s, while overnight lows will drop into the 20s amid excellent radiative cooling conditions. Generally expect clear and quiet conditions each afternoon...with the main concern being potential for low RHs co-located with breezy afternoon winds. Right now, overlap warranting any red flag products is pretty scant...and the thinking is that ample rainfall associated with the Tue/Wed system should moisten fuels enough to preclude a significant fire weather threat. The forecast will nonetheless need to be monitored over the coming days.

By Saturday night, much of the eastern CONUS will find itself beneath a nebulous upper pattern, with mostly flat, unconstrained z500 flow. Embedded upper vorticity will gently steer a cold front across the Ozark Plateau and into the Southeast by Sunday or Monday...resulting in precipitation developing sometime near the end of the period. The details remain murky, however - faster guidance like the EC and many of its ensembles bring precip into the area as early as the predawn hours Sunday; slower guidance like the GEFS keep us dry until after the end of D7. Depending on how exactly things flesh out...frozen p-types aren't out of the question...but it's far, far too soon to make any determines as to what this system may look like.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Expecting VFR conditions to prevail for a bit longer than previously fcst, with restrictions not expected until around daybreak for the Upstate terminals and KAVL and a few hrs later for KHKY and KCLT. Cloud cover will gradually in- crease with mid to upper-level clouds moving over the terminals thru the evening. As better moisture moves into the area, expect cigs to go MVFR around daybreak and then IFR a few hrs after that. I don't have any prevailing SHRA until mid to late morning for KAVL and the Upstate terminals with prevailing SHRA at KHKY a few hrs after that. At KCLT, prevailing showers aren't expected until later Tuesday evening with PROB30s before that. Sct showers will continue thru the day and into the evening, however cigs should improve somewhat at the Upstate terminals by the late aftn/early evening. Cigs at KAVL and KHKY are more likely to remain IFR thru the end of the taf period. Winds will be light and from the E/SE tonight and early Tuesday with some sites going calm overnight. Winds will pick up from the S tomorrow aftn, and remain S to SW thru the evening. At KAVL, winds will be light and from the S/SE thru the morning. They will pick up again from the S by the early aftn and remain SLY thru the evening. In addition, KAVL can expect a few hrs of LLWS during the early to mid aftn.

Outlook: Numerous showers and possibly a few thunderstorms with associated restrictions are expected late Tuesday into Wednesday as a moist cold front moves thru the area. Drier and predominantly VFR conditions should return by Wednesday aftn and linger thru late week.

GSP WATCHES/WARNINGS/ADVISORIES

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