textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Rainfall amounts trending higher for Wednesday. Temperatures trending cooler for the weekend.

KEY MESSAGES

1. Quiet conditions continue for most of Monday before a decaying convective line crosses the area Tuesday morning. 2. Two frontal systems bring rain chances Wednesday and again early in the weekend.

DISCUSSION

Key message 1: Quiet conditions continue for most of Monday before a decaying convective line crosses the area Tuesday morning.

A weak and ill-defined surface low is analyzed offshore of the Chesapeake Bay region and continues to drive weak low-level CAA across the NC Piedmont and, to some extent, the SC Upstate. This has, in a manner uncharacteristic of Carolina-style CAA, had the effect of actually advecting slightly higher dewpoints into the region through the 1000-850mb layer, and in response an extensive deck of stratocu has developed across most of our NC zones.

The latest RAP forecasts and REFS profiles depict a PBL that never fully decouples overnight, owing in large part to that sustained CAA and weak, shallow mixing. Consequently, not expecting an issue with patchy fog tonight as we had last night. Thickening stratocu will, however, impact Monday morning's lows. With virtually none of the guidance keeping a good handle on the extent and thickness of cloud cover across the I-77 corridor, it seems likely that as a result, lows may overshoot the forecast by a couple degrees there. But all told it should be a quiet night across the western Carolinas.

Monday will be a quiet, transitional day for the most part. Stratocu should retreat quickly after sunrise, giving way to mostly-clear skies all day, with some cirrus and perhaps a shallow afternoon cu field. Not much support for afternoon gusts Monday, even in some of the more aggressive ensemble runs.

By Monday night, a mature surface low will be located over Wisconsin, with attendant cold front extending across Illinois and into the Ozarks. Most of the hi-res models - both the new 00z HREF members as well as the recent REFS ensemble guidance - depict an MCS ejecting off this boundary on Monday evening and tearing across the Tennessee Valley through Monday night, and making a run at our NC mountain zones through early Tuesday morning. By dawn Tuesday, decaying convection should be on our western doorstep. Given its timing...arriving near the diurnal min and crossing the CWA during the morning and early afternoon hours on Tuesday...the convective environment won't exactly be conducive to severe weather, and the mountains should be enough to disrupt its balance and kill it. This is what most of the CAMs depict. Still, can't entirely rule out a rogue damaging wind gust somewhere as the remnants cross the CWA early Tuesday.

Key message 2: Two frontal systems bring rain chances Wednesday and again early in the weekend.

Model guidance no coalescing around a solution showing two frontal systems bringing rain chances to the area Wednesday and again late Friday into Saturday. A cold front moves into the area Wednesday. A wave of low pressure forms along the front as it moves through. This along with an associated shortwave will provide plenty of forcing for precipitation. Weak instability also develops with scattered thunderstorms expected along with the widespread showers. A moderate amount of bulk shear also develops. Scattered thunderstorms are expected along with the widespread showers. It is still uncertain whether the combination of these features will be enough for any severe storms to form, but the potential is there. Deep moisture also moves in ahead of this system with PW values approaching 200 percent of normal. This combined with plenty of forcing could lead to some heavy rainfall, mainly across the mountains. The overall flood threat is low given the recent drought conditions and quick movement of this system, but it bears watching.

Dry conditions expected Thursday as the front moves south of the area, but the next weather maker develops in the form of a Gulf Coast low pressure system which moves by to our south on Saturday. Moisture and precip chances begin ramping up late on Friday and spreading across the area Friday night into Saturday. The guidance does differ on the exact track of the low pressure, so PoP is currently in the chance range and QPF is moderate at best. This could change in either direction depending on the actual track of the low. Dry high pressure returns for Sunday. The airmass associated with the high will be on the cool side and frost/freeze conditions could become a concern across the mountains Saturday night.

AVIATION /06Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: An extensive stratocu deck has expanded across most of the NC Piedmont and mountains. An equipment failure has impacted our ability to receive ceiling observations at KHKY, but surrounding obs in the foothills (most notably KMRN and KFQD) indicate variable ceiling/non-ceiling cloud bases in the FL020-030 range, so it's a safe bet that at least intermittent MVFR ceilings are developing or have developed at KHKY. Also think occasional MVFR ceilings could develop at KAVL and KCLT for the next several hours. The Upstate sites, where moisture is shallower, have a lower probability of seeing any restrictions develop. For all sites, a sustained 3-5kt wind overnight should preclude much of a fog concern. Expect low clouds to scatter out quickly after daybreak, with mostly just cirrus and continued S/SSE winds for most of the day Monday. A cold front and associated precipitation will approach the western fringe of the terminal forecast area on Monday night...but currently can only a justify a PROB30 for SHRA during the final hours of the 06z KAVL TAF, early Tuesday morning. Elsewhere, precipitation should hold off until after the end of the TAF period.

Outlook: A decaying convective system will cross the area early Tuesday, bringing widespread showers, possible embedded thunder, and associated flight restrictions. Active weather will continue into mid-week, with another disturbance expected on Wednesday/Wednesday night.

GSP WATCHES/WARNINGS/ADVISORIES

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