Sunrise 6:26 AM   Sunset 8:13 PM Moonrise 3:23 AM   Moonset 3:28 PM

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FXUS62 KGSP 040604 AFDGSP

Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 204 AM EDT Sat May 4 2024

SYNOPSIS
A front will stall over the region through the weekend resulting in periodic showers and thunderstorms. The best chance for widespread showers and thunderstorms can be expected today into tonight, with only scattered activity expected on Sunday. A general summertime pattern sets up early next week, which will keep scattered thunderstorm chances around each afternoon. Highs will trend well above normal by Tuesday, remaining well above normal through at least Thursday.

NEAR TERM /THROUGH TODAY/
As of 150 am EDT Saturday: An upper ridge axis persists near the SE Coast. Isolated-to-scattered convection persists this morning upstream of the ridge, generally ahead of an approaching shortwave trough. Little change in the pattern or vertical profiles will occur overnight, such that a few hundred joules of MUCAPE will linger in southerly flow regime. Thus scattered showers and a few t-storms are expected to continue, mainly across western areas over the next 1-3 hours. However, signals in convection-allowing guidance remain relatively strong that the main focus for scattered/perhaps numerous convective coverage will shift to the eastern third or so of the CWA toward sunrise. The main threats from any storms/deeper showers are expected to be locally heavy rainfall and occl c-g lightning.
Outflow from earlier storms left behind a nearly saturated PBL in some spots, and some locally dense fog can't be ruled out in such areas this morning. Min temps will be well above normal.

Convective coverage should increase throughout the daylight hours as forcing from the approaching trough increases. Instability and shear will remain on the weak side, while forecast profiles show an even more saturated atmosphere...with PWATs in the 90th-99th percentile for this date. This suggests even less chance of strong to severe storms, with an uptick in the heavy rain potential. That said, the overall flood risk remains low given the dry antecedent conditions.
Highs will be near normal due to clouds and precipitation.

SHORT TERM /TONIGHT THROUGH MONDAY/
As of 240 PM EDT Friday: The rest of the weekend looks active right into the first part of next week. A baggy upper trof overhead on Saturday night slowly lifts northeast with a short wave passage, and this bit of lingering forcing will be able to keep shower/thunderstorm activity on a slow wane into the early morning hours. Guidance suggests that it will never die off entirely, so the fcst retains some fairly high precip probs. That sets the stage for Sunday. Models show less forcing, but an uptick in the available buoyancy in the afternoon. That should make for a more thermodynamically-driven day, with better than climo coverage of showers and storms. Forecast soundings off the NAM show some pulse-severe wind damage potential with mid-level dry air and a shallow inverted-V, so it would not come as a surprise if it was a busier day than Saturday. A stronger short wave lifting northeast over the TN/OH Valley regions on Monday will continue to support diurnally-enhanced convection, so we continue with above climo precip probs. Temps look to be on the order of five degrees above normal.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
As of 200 AM EDT Saturday: Weak upper ridging builds into the Carolinas on Tuesday while an upper shortwave tracks overhead the forecast area. This will act to keep shower and thunderstorm chances around across most of the forecast area. Have the highest PoPs (likely) confined to the NC/TN border, with chance PoPs elsewhere (the exception being the far southern tier of the CWA where there are no mentionable PoPs). With shear values expected to range from 25-35 kts and SBCAPE values around 1500 J/kg on Tuesday afternoon, isolated strong to severe storms seem plausible. Tuesday night into Wednesday weak upper ridging will continue building across Carolinas. This should generally lead to lower convective chances compared to Tuesday. Thus, capped PoPs to chance across the western two-thirds of the forecast area. However, since cloud cover is currently expected to be lower on Wednesday, global models depict SBCAPE ranging from 1500-2500 J/kg during peak heating, with shear still generally ranging from 25-35 kts. Thus, diurnal strong to severe storms will be possible again on Wednesday. At the sfc, a cold front will slowly progress eastward out of the central US but will remain well west of the Carolinas. This will lead to W/SW'ly 850 mb flow in place Tuesday into Wednesday, allowing temps will climb into the mid to upper 80s east of the mts and across the mtn valleys each afternoon. A few locations along I-77 in the southern NC Piedmont may even see highs reach 90 degrees on Wednesday. Thus, highs should end up around 6-12 degrees above climo. Lows Tuesday night and Wednesday night should end up around 12-15 degrees above climo thanks to some lingering cloud cover and SW'ly sfc winds.

The aforementioned cold front will continue trekking eastward Thursday into Friday leading to better shower and thunderstorm chances for the western Carolinas as well as the potential for locally heavy rainfall (especially for areas that received rainfall earlier in the week). Convection will be in place well ahead of the front Thursday into Friday so have chance PoPs painted across the entire area. The only exception is the NC mtns where likely PoPs are in place for Thursday. The actual FROPA itself should track across the western Carolinas Friday afternoon into early Friday evening.
The front will allow shear values to increase slightly, ranging from 35-45 kts. Guidance shows SBCAPE values ranging from ~1500-2000 J/kg on Thursday afternoon so the potential for strong to severe storms will return once again. Depending on how fast activity pushes south and east on Friday, the potential for strong to severe storms may return again Friday afternoon (mainly along and east of I-85). Temps will climb back into the mid to upper 80s Thursday afternoon across the mtn valleys and east of the mtns. A few locations along I-77 in the southern NC Piedmont may once again see highs reach 90 degrees.
Slightly cooler temps can be expected on Friday behind the cold front, with highs only climbing into the lower to mid 80s east of the mtns. Lows Thursday night will remain ~12-14 degrees above climo, becoming ~5 degrees above climo Friday night behind the cold front.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/
At KCLT and elsewhere: Very messy aviation forecast this period, as unusually high moisture levels for the time of year combined with weak lift and instability will yield periods of convection and cig/ visby restrictions through much of the period. Isolated convection, including some TSRA is ongoing across the area early this morning, warranting VCTS at KAND/KGMU. The convective potential as well as the likelihood of lowering cigs is expected to steadily increase toward sunrise, warranting tempos for SHRA and IFR/MVFR conditions.
Can't rule out a TSRA during this time frame, but believe the potential should be higher later in the morning into the afternoon.
Cigs are forecast to settle to IFR by late morning, with conditions expected to be slow to improve into the afternoon. The potential for TSRA warrants a Prob30 for such at all sites from late morning through much of the afternoon. This is accompanied by categorical SHRA and MVFR visby. The convective potential is expected to steadily decrease toward the latter few hours of the period.
However, at least VCSH is warranted Sat evening into the early part of Sunday. Any modest improvement in cigs/visby during the afternoon will be reversed by late evening.

Outlook: Enhanced moisture will combine with a weak/stalled front through early next week, resulting in a period of active/mainly diurnal convective weather each day. There will also be the potential for restrictions associated with widespread fog and/or low clouds each morning.

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

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