


Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
327 FXUS62 KGSP 171818 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 218 PM EDT Sun Aug 17 2025 .SYNOPSIS... Rain chances through Tuesday are mainly confined to the mountains. Hot and humid weather starts the week, but temperatures trend cooler Tuesday, ending up near normal through Thursday. Rain chances increase at the end of the week with temperatures a few degrees below normal. && .NEAR TERM /THROUGH MONDAY/... As of 1245 PM Sunday: The deep convection appears to be a bit delayed compared to the last few days, but satellite imagery shows enhanced ridgetop cu, so a few showers should pop up momentarily. The environment has 2000-3000 J/kg of sfc-based CAPE, though that should drop a little bit into peak heating as the dewpoints mix out a little bit. Still think the model blend is undercooked with the possible extent of the deep convection today, even more so after seeing the 12Z CAMs on the HREF page, so precip probs were bumped up closer to climo across the mtns/foothills for the afternoon. The area S of I-85 could see an isolated shower or storm as well. The mid-levels are much drier today compared to the past few weeks, so it might be tough for anything to really get going because it will have to overcome the dry air entrainment, but if it can, there`ll be enough dCAPE to allow for some strong downdrafts and sfc wind gusts. Temp/dewpt trends appear to be in decent shape, so no changes to the high temp fcst. The shower activity should diminish with sunset. Another quiet night is planned as the axis of a mid/upper ridge extending from the anticyclone over the Plains shifts northward. After we get rid of whatever convective debris clouds we have floating around, we should be able to cool off enough for another round of mtn valley low stratus and fog. Meanwhile, a weak remnant cold front/outflow boundary will probably be hanging out to our north overnight. That boundary may help out Monday to increase the precip chances and coverage through the afternoon as it settles down across the region, as the convective environment looks otherwise nearly identical to today. The CAMs indicate better coverage in the afternoon, so precip chances might end up on the higher side of climo. Monday will probably be the warmest day of the week with temps topping out a few degrees above normal, but the heat index should stay just under advisory criteria. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... As of 200 PM EDT Sunday: Highs on Tuesday are expected to be about 6-8 degrees lower than Monday, or slightly below-normal, as transient high pressure moves off the New England coast and weak, deep-layer NEly flow advects a modified maritime airmass off the Atlantic. This will support increasing PoPs area wide, with high-end chance to likely PoPs currently progged across the mountains Tuesday afternoon under weak upslope flow. Instability looks to be quite anemic for August as profiles look fairly warm, resulting in poor lapse rates and SBCAPE values below 1000 J/kg. Parcels may also have to contend with an inversion between 750-800mb; therefore, strong/severe storms are not a concern. Despite very weak steering flow, limited instability will make it difficult to realize the entirety of the 1.7-1.9" PW values across the area and the excessive rainfall threat also appears to be quite marginal. By Wednesday morning, the forecast area will be sandwiched between Hurricane Erin well off the Carolina coastline and an approaching weak cold front over the Tennessee Valley. The front is expected to enter the mountains by Wednesday afternoon and should provide enough low-level convergence to justify PoPs similar to Tuesday across the mountains and foothills. However, lapse rates are even shallower than Tuesday given increasing temperatures throughout the mid- and low-levels with a persistent low-level inversion to further suppress instability. Therefore, away from the front across the Piedmont, PoPs decrease to slight chance. PWs are also lower given a subsident column on the fringes of Erin`s influence, as evident by forecasted mid-levels drying. As such, Wednesday looks to be even less threatening in terms of a strong storm and hydro threat. Temperatures will be similar to Tuesday as the area is still under the influence of a weak NEly flow, though decreased cloud cover given the drier column supports highs perhaps a degree or two warmer, or near normal for mid-August. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 200 PM EDT Sunday: General troughiness will dominate the upper-level pattern over the southern Appalachians through the end of the work week as Hurricane Erin thankfully recurves out into the Atlantic and a sprawling anticyclone keeps the western US hot. The weakness aloft will keep the area unsettled ahead of a potent shortwave trough dropping into the upper Midwest by Friday. A weak warm front may also be draped across central GA into SC Thursday, and guidance is suggesting isentropic lift north of the front will work to enhance coverage of showers and storms. Therefore, chance (Piedmont) to likely (mountains) PoPs are forecasted on Thursday and will continue into Friday within low-level southerly flow. Unlike earlier in the week, the column is a bit cooler. The resultant steeper lapse-rates will increase instability which may drive more impressive rainfall rates within a persistently moist column. Therefore, the better strong storm/excessive rainfall threat will likely occur later in the work week. The other main story will be high temperatures, as the mostly cloudy skies and higher convective coverage will suppress the diurnal range. Expect highs to be a couple of degrees below normal on Thursday and potentially 5-7 degrees below normal for Friday. Heading into the weekend, shortwave propagation and amplification around a deep upper-level low near James Bay will develop a longwave trough over the eastern ConUS as an attendant cold front approaches the area later Saturday from the northwest. This pattern supports a continued relatively cool and unsettled forecast for the weekend with numerous to widespread showers and storms likely. A continued excessive rainfall threat is likely through the end of the period, especially given the near-term antecedent conditions. Expect highs to be 7-9 degrees below normal on Saturday, with some modest warming on Sunday if the timing of the next FroPa is indeed post-daytime heating as the NBM suggests. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... At KCLT and elsewhere: Widely scattered showers and storms have developed due to differential heating over the higher terrain early this afternoon. Will include a PROB30 for thunderstorms over the mtns and the Upstate based on radar trends and CAM output. The storms should diminish at sunset. Any flight restrictions at those places will be kept in the PROB group. Otherwise, prevailing VFR. Meanwhile, at KCLT, there could be an occasional bkn VFR ceiling through the afternoon. Wind will be light and variable across the region, but will favor a northerly direction more than anything else. After sunset, another quiet night with cirrus and a light/variable wind. Expect another round of mtn valley low stratus and fog, so KAVL gets the prevailing VFR/temporary IFR around daybreak. Otherwise, the day should be very similar to today. Will hold off with any mention of showers/storms for now. Outlook: Afternoon showers and thunderstorms with associated restrictions are expected mainly across the mtns Mon-Wed. Chances currently fcst at all terminals Thu. Morning fog and low stratus are also possible, especially across the mountain valleys each day. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...DEO NEAR TERM...PM SHORT TERM...JMP LONG TERM...JMP AVIATION...PM