Sunrise 6:16 AM   Sunset 8:26 PM Moonrise 2:03 PM   Moonset 2:18 AM

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FXUS62 KGSP 171104 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 704 AM EDT Fri May 17 2024

SYNOPSIS
A warm front and weak low pressure system will bring frequent chances for showers and thunderstorms today through the weekend. Somewhat drier conditions return early next week resulting in only isolated afternoon and evening showers and storms Monday and Tuesday.

NEAR TERM /THROUGH TONIGHT/
As of 640 AM Fri: Abundant cirrus are creeping in as upper ridge axis migrates east and net cyclonic flow develops aloft, with trough slowly exiting the southern Plains and lower MS Valley. Vort maxes left over from overnight Gulf Coast MCS look to advect northeast to our vicinity later this morning, but latest CAM output suggests this will have less energy to work with and there appears a low chance of showers/storms developing as a result. Sprinkles will be associated with the thickening cirrus. Meanwhile, warm front will shift northward thru the Deep South, associated with developing sfc low in MS/AL. The approach of this front warrants further increases in PoP and expansion across the rest of the CWA in the afternoon, perhaps along with diurnally driven showers/storms, with likely to categorical chances for the whole area by late evening. This second round of precip is more likely to induce thunder, particularly in our southern half, with deep convection possible albeit most likely elevated from the warm frontal inversion. This MUCAPE appears meager enough that severe wx looks unlikely. Peak PoPs will follow the warm front, behind which moist layer becomes more shallow albeit with weak upglide continuing. Low stratus are likely to develop in the evening and persist into Saturday; unclear at this time whether the end of precip will be associated with fog formation but a mild, muggy night appears a good bet. WPC Marginal Risk seems to adequately cover the area most likely to see convective rainfall rates thru tonight.

The clouds and showers will keep temps a few degrees below normal in the west, but still may rise a degree or two above normal in the east where these are less of a factor.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
As of 245 AM EDT Friday: A positively tilted southern stream upper trough will cross the TN valley on Saturday providing some QG forcing atop the FA during peak heating. Precip from Friday night may cause a frontal boundary to set up roughly along or just north of the I-20 corridor early Saturday. The air mass south of the boundary will be fairly unstable along with good bulk shear of 40-50 kt. For our forecast area, CAPE looks to be 1500 J/kg or less, with the various deterministic models showing the maximum sbCAPE in differing parts of the area. Shear will also not be quite as high as to our south. So this muddies the severe threat quite a bit. The latest CAMs show a rather disorganized convective mode across the CWFA Saturday, and a marginal risk in the SPC Day 2 Outlook seems reasonable. With more convection expected to our south, and veering deep-layer flow to nearly due westerly, will also limit excessive rain potential, as PWATs trend down. Despite plenty of cloud cover, highs will be near normal with humid low-mid 60 dewpts.

The low pressure system slows down once it reaches the NC Coast Sunday morning, with the CWFA in the NELY-flow side of the system. Wrap-around moisture should keep skies cloudy to mostly cloudy with showers and mainly general thunderstorms possible. The air wrapping around the system should be less unstable and bulk shear will generally 20 kt or less, so severe thunderstorm chances will be low. Heavy rain may localize along the escarpment with nearly parallel deep-layer flow and some ELY upslope, but overall, no strong signals for excessive rainfall/flooding. Highs will be kept below normal, especially across the NC foothills and Piedmont.

LONG TERM /MONDAY THROUGH THURSDAY/
As of 315 AM EDT Friday: The low pressure system along the NC coast should drift far enough east to allow more dry air to work into the forecast area from the N/NE on Monday. This should allow for more breaks in the clouds and lower precip chances. With more insolation, could see diurnal convection across the mountains, with isolated showers possible across the Piedmont, but severe storm threat should remain low. Temps will be slightly below normal thanks to continued cool NELY flow. High pressure builds in Tuesday, making for largely dry wx across the area and temps returning to normal.

The 00z medium range guidance has come into better agreement on the next cold front to affect the forecast area. Earlier guidance had moisture and PoPs returning Wednesday, but now have backed off. So Wednesday may end up being dry with temps warming to slightly above normal. With an upper ridge building over the Southeast, the front will weaken as it tries to push into the area Thursday. The 00z guidance shows meager QPF response with the front, and isolated to scattered convection is expected. The NBM PoPs may be a little overdone, if this trend holds, but for now will keep the solid chc PoPs in there. Slightly above-normal temps will continue thru the end of the week.

AVIATION /11Z FRIDAY THROUGH TUESDAY/
At KCLT and elsewhere: Relatively low confidence TAFs with multiple sources of weak forcing and differing signals among guidance members. Widespread cirrus associated with onset of cyclonic flow aloft which will permit weak vort lobes to pass over the region. Only very modest CAPE looks to develop the remainder of the morning, and earlier expectations of early day SHRA/TSRA have diminished. Cirrus deck however may bring a few sprinkles by late morning. Some destabilization appears possible near peak heating, when convective layer deep enough for TSRA at some of the terminals. More widespread precip arrives with warm front tonight and more isolated embedded TSRA are possible tonight. Warm front appears likely to produce MVFR and then IFR cigs tonight, with areas of fog developing after precip. Generally southerly winds this period. Slow improvement out of IFR after 12z Saturday morning.

Outlook: Periods of convection, which could be widespread at times, are expected through the weekend. Late night/early morning restrictions in low stratus and/or fog will also be possible. Drier weather is expected to return early in the next work week.

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

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