Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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119 FXUS62 KGSP 250455 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1255 AM EDT Tue Jun 25 2024 .SYNOPSIS... Dry and less humid conditions continue today before the heat and humidity returns Wednesday ahead of an approaching cold front. This front will bring showers and thunderstorm chances back to the area late Wednesday into Thursday. Hot and humid conditions will persist into the weekend with a chance of showers and thunderstorms each afternoon. Another cold front approaches the area late this weekend keeping unsettled weather around. && .NEAR TERM /THROUGH TODAY/... As of 100 AM EDT Tuesday...No major changes were needed as the forecast remains on track with dry and clear conditions in place. Otherwise, in light of today`s dewpoint crashing, opted to make some tweaks to tomorrow`s dewpoints, as GFS and NAM forecast profiles depict even drier air aloft. Mixing potential is still in question given a steeper subsidence inversion than today`s likely to be in place across the area; still, it seemed reasonable to bring values down a little, to at least match the latest hi-res guidance blend. A small-scale sfc high currently located over WV will migrate southeast and off the Carolina coastline thru the period and keep winds unfavorable for sfc-layered moisture transport, thus a morning fog threat will be nil especially with the pressure gradient remaining a little tight allowing for weak sfc mixing. On Tuesday, expect the upper ridge to remain dominant and large scale subsidence negating any precip/thunder. Lows this morning will remain a couple degrees above normal, while highs once again rise above normal by 5- 7 degrees due to great insolation. && .SHORT TERM /TONIGHT THROUGH THURSDAY NIGHT/... As of 230 PM Monday...The hottest temperatures of the forecast are expected for Wednesday ahead of an approaching cold front. Highs in the mid- to upper 90s east of the mountains are expected Wednesday afternoon, with highs in the lower 90s in the mainstem mountain valleys. These highs will still be about 3-5 degrees below long-standing records. Dewpoints Wednesday afternoon are expected to reach the mid- to upper-60s which would be enough to push heat indices to the 100-102 range in typical locations including Charlotte and the Upper Savannah River Valley, but nothing unusual for this time of year. Despite deep-layer mixing and high cloud bases; SBCAPE values of 1500-2000 J/kg are expected with steep low-level lapse rates; therefore, the approaching shortwave energy and the mountain terrain should provide enough forcing for scattered shower and thunderstorm development, especially across the mountains. Bulk shear values of less than 20 kts precludes any significant concern for severe weather; however, ample dry-air aloft/downdraft CAPE suggests a strong downburst or two cannot be ruled out. Overall, given underwhelming moisture content through the column, we are not expecting notable precip outside of isolated locations with this activity. The latest guidance stalls the front near or just to the south of our forecast area for Thursday. Compared to Wednesday, the resultant airmass is actually a bit more moist through about 500mb, especially in the mountains. Lapse-rates aren`t as steep through the mid-levels as on Wednesday, but the LCLs/cloud bases are expected to be a bit lower as well. Forecast soundings suggest unimpressive SBCAPE values below 1000 J/kg, but the proximity of the decaying frontal boundary should be enough for another round of scattered showers and general thunderstorms, with numerous showers and thunderstorms possible over the mountains thanks to typical terrain-induced forcing/enhancement. Bulk shear values remain below 20kts; therefore, we still lack a notable severe storm threat. National Blend guidance is a bit more aggressive with PoPs Thursday afternoon than preferred given the profile and pattern, but this will be another high PoP/low QPF scenario with little appreciable rainfall expected outside of isolated locations. Expect little moderation behind the front east of the mountains with highs 2-4 degrees "cooler" than Wednesday, but still 2-4 degrees above normal. The influence of the front will be a bit more discernible in the mountain valleys, with highs 5-7 degrees cooler than Wednesday, though these highs will still be slightly above normal. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 230 PM Monday...The extended period will feature a resurgence of the heat ridge over the Lower Mississippi River Valley, keeping our area on the southern fringe of the active westerly flow across the northern half of the ConUS. This upper-level pattern suggests that we should be able to maintain diurnally driven isolated to scattered shower and thunderstorms Friday and Saturday with the best coverage in the climatologically favored mountain zones. Once again, there is not enough forcing or moisture to suggest any notable relief from ongoing dry conditions. High temperatures are expected to remain several degrees above normal through Sunday, with low-level flow gradually becoming more conducive for moisture advection from the Atlantic and eastern Gulf. Therefore, expect increasingly humid conditions heading into the weekend, as the next cold front approaches the area later Saturday into Sunday. It may become increasingly difficult to mix out the low-level moisture and current guidance suggests afternoon dewpoints into the lower 70s are likely Saturday and Sunday. If this materializes, we can expect more widespread heat indices in the 100-104 range across the Piedmont, especially on Sunday when our high temperatures peak in the 94-97 range. The aforementioned moisture flux into the region through Sunday may put us in a better position for more notable convective coverage and rainfall along and ahead of the cold front, which is currently expected to enter the area later Sunday. While it is much too early to get our hopes up, the favorable return flow may allow PWs to approach 1.75-2 inches with ample instability. Bulk shear values look anemic at this time, so the primary focus here is improved coverage and better opportunities for some much-needed rainfall. At this time, the front is expected to clear the area by Monday morning. If this occurs, we can expect max temperatures several degrees lower than Sunday, though we may see little relief from the humidity. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: VFR thru the period as we remain a dry and suppressed post-frontal regime. Surface high pressure will migrate into the area over the next 12 hours or so, permitting winds to turn N overnight, and eventually to the ENE during the day tomorrow as it pushes out to the coastal plain. They`ll never quite die down overnight, with most sites retaining a 2-4kt wind even in the wee hours before dawn. Another cu field should break out tomorrow by mid to late morning, but absolutely no chance of any shower development. For KCLT, the TAF period extends far enough out for winds to turn S of E after dark Tuesday evening. Outlook: Widely scattered SHRA/TSRA may return Wednesday afternoon/evening, with seasonable summertime weather lingering into the weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...AR NEAR TERM...AR/MPR/SBK SHORT TERM...JMP LONG TERM...JMP AVIATION...MPR