Sunrise 6:42 AM   Sunset 8:02 PM Moonrise 4:11 PM   Moonset 4:14 AM

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FXUS62 KGSP 200728 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 328 AM EDT Sat Apr 20 2024

SYNOPSIS
Unseasonably warm weather will continue today with isolated showers and thunderstorms possible for the Piedmont locations during the afternoon. Much cooler temperatures and widespread light rain is expected Sunday with drier weather on Monday. Drier and warmer weather will return to the area Tuesday through next week.

NEAR TERM /THROUGH TONIGHT/
As of 323 AM EDT Saturday: The rest of the pre-dawn hours should be fairly quiet, altho a rogue shower could still pop up anywhere as a weak frontal zone drops down over the region. There remains also a small chance of showers near the TN border due to a westerly upslope flow of moisture. Temps should remain mild owing to the mid/high cloud cover.

Over the next 24 hours, the western Carolinas and northeast Georgia will remain under a nearly-zonal flow that will have some weak vorticity moving across the Southeast, but nothing significant. The flat flow should allow for a weak cold front to lay down and move south across the SC/GA part of the fcst area today and then stall closer to the Gulf Coast tonight. Along this boundary, some weak convergence will persist into the afternoon, enough so that a few of the CAMs manage an isolated thunderstorm or two east of the mtns. The RAP/GFS manage about 1000-1500 J/kg of sfc-based CAPE this afternoon, but unlike yesterday, the effective shear is only about 25-35kt and from the west
So
not quite as favorable as yesterday...when we saw the development of a few supercellular storms east of the mtns...but still enough instability and shear to support an mini-supercell-like storm or two...which the HRRR hints about. Will include a small chance of storms and will also mention the isolated severe storm chance in the HWO. Temps will not be as warm as yesterday, but still on the order of five degrees above normal. Any isolated convection will end with the loss of daytime heating, and with that concluded, we will await the development of isentropic upglide that should develop ahead of a broadly-defined srn stream wave moving into the MS Delta region early Sunday. The CAMs agree that light precip will develop/spread northeast into the fcst area after midnight...to what extent remains a bit unclear. Either way, we should be on our way to developing a cold air damming wedge by daybreak Sunday. Overnight low temps will be about a category above normal, but this should be one of those odd situations when the calendar day high temp occurs right after midnight, and the calendar day low happens late in the day.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/
As of 145 AM EDT Saturday: Baroclinic zone stretching from the Lower MS Valley through the Southeast, while a stalled boundary sets up shop over the Gulf Coast will help set the stage for increasing PoPs on Sunday. A coastal wave will ride along the boundary and slip east through S GA/Fl Panhandle during the daytime period Sunday. The associated precip shield will overrun the entire CFWA, but lack of instability should keep rain rates at bay, with light to moderate QPF response. Factor in a strong surface high settling over the Central High Plains, with a piece of the high breaking off over the Mid-Atlantic, and an in-situ wedge will nose into the region with north-northeasterly flow at the surface. Precip overriding this stable dome will help to lock it in. As a result, temperatures will run 15-20+ degrees cooler compared to Saturday. Most of the rain should taper off by Sunday evening as the coastal low shifts offshore, into the western Atlantic. High temperatures for Sunday may occur early Sunday morning before the sun rises as temperatures in the afternoon will struggle to get out of the 50s for most locations. In-situ wedge will lingering over the area Sunday night into Monday before the surface high centers over the area by Monday night. Overnight lows on Sunday will run on the cool side as most locations are forecasted to run 5-10 degrees below normal, but elevated winds at the surface ultimately shuts down any frost potential across the active growing zones. Temperatures will rebound slightly on Monday, but should remain ~10 degrees below normal with continued north-northeasterly flow and colder air aloft thanks to a quick moving shortwave trough that will swing over the CFWA during the daytime period. Monday night will be the coldest night as light winds and mostly clear skies lead to good radiational cooling conditions. Tight dewpoint depressions and temperatures should remain just warm enough to avoid any frost development, but if trends lean slightly cooler between now and then, the southern/central mountains of NC and the I-40 corridor zones could end up with a Frost Advisory as overnight lows will run 5-10 degrees below normal.

LONG TERM /TUESDAY THROUGH FRIDAY/
As of 300 AM EDT Saturday: An upper trough will swing into the eastern CONUS late Tuesday into Wednesday with an attendant boundary. Model guidance produce a moisture starved fropa with only a light QPF response along the NC/TN border during the day Wednesday. With the better forcing confined to the north and east, not expecting much besides a wind shift across the CFWA. Temperatures will rebound Tuesday and Wednesday ahead of this feature as heights recover and the flow turns out of the south-southwest with near-normal values Tuesday and slightly above for Wednesday. Northwesterly flow aloft will remain in place through the middle part of next week with surface high settling over the northeastern CONUS. In this case, airmass modification will take more time than normal to occur. Current trends indicate that upper ridging will build back in by D6/D7 of the period with an unsettled synoptic pattern beginning to traverse from the central CONUS towards the eastern CONUS, but this activity is beyond the current forecast period.

AVIATION /08Z SATURDAY THROUGH WEDNESDAY/
At KCLT and elsewhere: Lingering showers have moved to the east of the fcst area. The main concern this morning is the possibility of ceiling/vis restrictions developing around metro Charlotte in the pre-dawn hours, given the showers and storms that moved through the region in the late evening. Some of the guidance has picked up on this and paints a pessimistic picture with an IFR ceiling restriction developing at KCLT before operations ramp up this morning. I consider this almost a coin flip at this point, so the TAF was written more optimistically and kept a TEMPO group for some MVFR clouds before daybreak. Hopefully by the time you are reading this, the atmosphere has shown its intentions with regard to the low ceiling development. The mtns are the other place where low level moisture could sneak in during the pre-dawn hours. An MVFR-level cloud deck on the west side of the mtns is expected to move up the valley to KAVL before sunrise, resulting in a ceiling restriction. Wind will be light/variable until a weak boundary moves thru, after which time light N to NE is favored. On Saturday, the fcst looks relatively benign. Wind should stay mostly N. A few of the models develop isolated storms again in the afternoon, but the chance is too low to include in any of the TAFs. Wind comes around to NE this evening and increases as the next system approaches from the SW. For now, the arrival of precip and moisture looks like it will be beyond the period, but not so at KCLT, where some might reach by the end of the fcst.

Outlook: Rain and possibly isolated thunderstorms are expected to develop on Sunday as a weak low pressure center passes just south of our area, likely resulting in restrictions for at least the southern part of our fcst area. Drier conditions return on Monday and linger into Tuesday.

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

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