Area Forecast Discussion
Issued by NWS Greer, SC

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817 FXUS62 KGSP 191911 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 311 PM EDT Mon May 19 2025 .SYNOPSIS...
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A stationary front remains over our region through Tuesday then drifts north as a warm front before a cold front approaches from the west by Wednesday. This keeps chances of showers and storms across our region until the cold front crosses. Cooler and drier conditions return in the wake of the front by Thursday and into the first half of the holiday weekend.
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&& .NEAR TERM /THROUGH TUESDAY/...
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Key Messages: 1) Isolated/scattered showers and thunderstorms this and Tue afternoon. 2) A couple of severe thunderstorms possible across ~the SW 1/3 of the CWA this afternoon. 2) Temps remain above normal. As of 145 pm EDT Monday: NW mid-level flow will continue through tonight...downstream of a steadily weakening ridge that is forecast to move over the southern Appalachians by the end of the period. Extensive high clouds associated with a series of decaying convective complexes continues over the area this afternoon, but with some thinning occurring from the southwest. A rather diffuse/quasi-stationary surface boundary remains draped across the area...separating lower70s/upper 60s dewpoints across the SW portion of our area from lower-60s dewpoints across the north. The combination of improving insolation and elevated dewpoints has resulted in an axis of 1500-2000 J/kg of sbCAPE from the upper Savannah River Valley into far southwest NC. A thunderstorm across extreme SE Tennessee is expected to ride along this instability gradient into our GA zones and western portions of the Upstate over the next 1-3 hours. Additional scattered convection is also likely to develop in these areas as the air mass destabilizes a bit more and interacts with the boundary, terrain features, and cold pools from ongoing convection. Convective potential will be limited be drier air across the northeast quadrant of the CWA, but token 20% chances are carried there compared to 30-50% across the remainder of the area. Deep layer shear will remain adequate for isolated organized convective structures and attendant damaging downburst and large hail threats across the southwest part of the area. Convection will diminish this evening, with only token slight chance PoPs advertised here and there through the overnight. Min temps will remain 5-10 degrees above climo. The boundary will remain over the forecast area early Tuesday, but is forecast to begin lifting north as a warm front by afternoon in response to large scale height falls to our northwest. Forecast soundings depict moderate levels of sbCAPE...especially with moisture pooling in the vicinity of the boundary...but also feature some degree of CIN to overcome. As a result, CAMs are somewhat reluctant to initiate convection...at least until evening. Nevertheless, the surface boundary and terrain effects should provide enough lift to allow for isolated/widely scattered convection by late afternoon, and general 20-30 PoPs are advertised across much of the CWA. Shear parameters are forecast to be a bit weaker through the daylight hours, but one or two severe storms will again be possible.
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&& .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY/...
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As of 310 PM EDT Monday... Key Messages: 1) Strong to severe storms are possible Tuesday evening into Tuesday night 2) Drier conditions gradually return on Wednesday with gusty winds developing 3) Temperatures cool off starting Thursday The main concern, possibly for the entire forecast period, revolves around the severe weather threat arriving from the west Tuesday after dark. Details are still somewhat sketchy more than 24 hours into the future, but there`s a decent chance that some sort of organized convection will reach the mtns in the late evening, perhaps in the form of a linear MCS posing the possibility of wind damage at least over the mountains. As per usual, the MCS would be running out of fuel as it comes across the Great Valley of TN after sunset, with the sfc-based CAPE dropping from about 1500 J/kg to about 500 J/kg once it moves into the mountains. However, shear will be sufficient to keep this activity potentially severe into the mtns, with effective bulk shear on the order of 45 to 50 kt and enough low level shear to keep the tornado threat mentionable. Note this will be enough shear and buoyancy to warrant the Slight Risk extending over the mtns and the expectation right now is for warnable storms into the mountains late Tuesday evening/night. For the most part, the line of storms would break up coming over the mtns as the time of day will be unfavorable. Only one or two of the CAMs have much in the way of anything east of the mtns. The short wave driving this forth will move across the fcst area by daybreak, thereafter only a token small chance of showers will remain on the TN border thru the day, while areas east of the mtns remain dry for the most part. Temps will remain above normal with the actual cold front, associated with an upper low traversing the Midwest/OH Valley, not crossing the region until late in the day or overnight Wednesday night. By that time, a cyclonic flow aloft around the upper low to our north will overtake the region, with weak sfc high pressure building in thru Thursday. This air mass should be drier than what we`ve had lately, and temps drop back to normal.
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&& .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/...
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As of 130 PM EDT Monday... Key Messages: 1) A drier air mass with below normal temperatures lingers into Memorial Day Weekend 2) Winds remain gusty through Friday evening 3) Shower and thunderstorm chances return on Sunday An atmospheric blocking pattern to our northeast will keep the cyclonic flow aloft in place through the end of the week as another upper low rotates down around the Great Lakes region on Friday to the Mid-Atlantic coast on Saturday. For the most part, a cool and drier NW flow will ensue for the first few days, perhaps with some light rainshower potential on the TN border Thursday night and Friday as a weak reinforcing sfc trof moves through, but chances are barely worth mentioning. Temps will be on the order of five to seven degrees below normal into the weekend before a warming trend begins as a flat upper ridge starts building in from the west on Sunday behind the departing upper low. Forecast uncertainty grows considerably at that point, as we are once again exposed to an MCS track Sunday into Monday with energy topping the flat upper ridge axis to our west both days. Details are highly sketchy at this stage, of course, so don`t give up on Memorial Day weather just yet, but there is decent support from a consensus of the model solutions for at least scattered storms. The forecast will feature a 30-40 prob for showers and thunderstorms with near normal temps on Monday.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/... At KCLT and elsewhere: VFR conditions across all terminals for the entire TAF period. Winds start out calm and should lightly pick up early this morning. Winds should pick up out of the WSW/SW by early afternoon. There is a slight chance for TSRA at most terminals this afternoon, but confidence remains low. Will keep a PROB30 as the chances have not increased enough to warrant anything higher. Timing if storms get going is between 18z-23z, with the earlier time for KAVL. Afterwards, winds turn more westerly and KHKY/KCLT turn more NE at the end of the period, but remain light. SCT cirrus and some mid-level cu today but all cigs remain VFR. Outlook: Showers and thunderstorms activity possible each afternoon through Thursday. Early morning fog/low stratus possible in the mountain valleys and locations, especially where rain falls the previous afternoon/evening. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...JDL SHORT TERM...PM LONG TERM...PM AVIATION...JDL