Sunrise 6:19 AM   Sunset 8:26 PM Moonrise 12:09 PM   Moonset 1:31 AM

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FXUS62 KGSP 151415 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1015 AM EDT Wed May 15 2024

SYNOPSIS
Low pressure brings showers and scattered thunderstorms to our region today. Brief high pressure brings a mainly dry day on Thursday. Showers and scattered thunderstorms return Friday and continue into the weekend. Isolated diurnal convection expected early next week.

NEAR TERM /THROUGH TONIGHT/
As of 955 AM EDT Wednesday: A reasonably robust cell over Cabarrus County will move east of the CWA within the half hour...leaving behind only some spotty/remnant showers across the northern tier of our zones. Otherwise, the latest water vapor imagery and surface analysis reveal an occluded cyclone over the eastern Ohio Valley, with the axis of a broad/deep layer trough extending through east TN. Over the course of today, the upper low will open into a trough as it translates east across the central Appalachians and Mid-Atlantic, with the base of the trough pivoting across the western Carolinas this afternoon, increasing upward vertical motion.
Meanwhile, veering/westerly low level flow is clearing out the low clouds across the western half of the area this morning, and this trend will continue into eastern areas through the morning, allowing for at least a couple of hours of strong insolation. sbCAPE is expected to range from 1500-2000 J/kg over much of the forecast area by mid-afternoon.

The combination of UVV and moderate instability should support initiation of scattered to numerous cells...initially over the mountains, with activity spreading E/SE along outflow boundaries through the afternoon and early evening. Deep layer shear is expected to gradually decrease through the day, as height gradient relaxes and flow becomes unidirectionally westerly through a deep layer. In fact, shear is expected to have decreased to 25-30kts by the time of peak convective coverage. Nevertheless, the shear/ buoyancy combo will support the potential for a few severe storms producing large hail and damaging wind gusts. An additional threat of localized heavy rainfall is expected, especially across the I-77 corridor and vicinity, where many locations have received 1.5 to 2.5 inches of rain over the past 36 hours. Storm motion generally looks fast enough to preclude a more widespread risk of flooding. Highs today will be around normal.

By late evening and into the overnight, a trailing cold front will arrive, scouring out moisture and instability. Skies will gradually clear (notwithstanding some lingering NW flow showers and associated cloud cover across the mountains) and winds will turn NW.
Models don't depict particularly robust postfrontal CAA, and so it's not expected to become particularly breezy. Temperatures will drop into the low 60s or even upper 50s in some locations.

SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
As of 255 AM EDT Wednesday: A short wave ridge moves in on Thursday along with a drier air mass. Still, there may be just enough lingering moisture for some diurnal showers along over the northern NC mountains and the I-40 corridor. Dry conditions expected elsewhere. Highs Thursday and lows Thursday night will be a few degrees above normal. Shower and thunderstorm chances ramp back up Friday and Friday night as an upper low and its associated surface low move toward the area. There is some disagreement on the speed and strength of this system, but there is good agreement on the sensible weather. PoP increases into the likely to categorical range. Instability and shear are relatively weak Friday but shear does increase during the evening. Therefore, severe storms are possible but uncertain. Isolated heavy rainfall is more likely given the high PW values and strong forcing. Highs Friday will be near normal with lows 5 to 10 degrees above normal Friday night.

LONG TERM /SATURDAY THROUGH TUESDAY/
As of 315 AM EDT Wednesday: Shower and thunderstorm chances remain high Saturday as the upper and surface systems move into the area.
Instability may be higher due to better lapse rates, but there is still uncertainty on severe chances. High PW values and strong forcing continue, so isolated heavy rainfall remains possible. The GFS and Canadian show a slower movement with this system, and keep scattered convection over the area Sunday. The ECMWF has been faster but is showing a slowing trend. Will keep scattered diurnal convection in place. Isolated to scattered diurnal convection possible Monday and Tuesday with lingering low level moisture and weak forcing. Highs near to slightly below normal Saturday rise to above normal by the end of the period. Lows bounce around normal through the period.

AVIATION /14Z WEDNESDAY THROUGH SUNDAY/
At KCLT and elsewhere: It's murky out there this morning. Periodic sprinkles with some embedded thunder across the NC Piedmont have disturbed otherwise foggy, cloudy conditions leading up to daybreak.
Widespread LIFR and isolated VLIFR flight restrictions in place, both for VIS and CIGs . Conditions should improve faster today than they did yesterday, becoming VFR sometime around late morning/early afternoon. More widespread convection is then expected as a lobe of upper energy arrives in the afternoon, coinciding with peak afternoon instability. All TAFs now include PROB30s/TEMPOs for TSRA and/or VCTS to handle this. Winds will generally be out of the S (SE at KAVL, SW everywhere elses) all day after a period of light and variable winds overnight. Once convection lets up Wednesday night, winds will turn around to WNW in the overnight period as a drying cold front slides into the area.
MVFR to IFR restrictions will return before daybreak Thursday, but lift quickly in the morning.

Outlook: Drying will continue Thursday, before convection and associated flight restrictions return ahead of a cold front over the weekend.

GSP WATCHES/WARNINGS/ADVISORIES
GA...None.
NC...None.
SC...None.

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