Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
Versions:
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
203 FXUS62 KGSP 280734 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 334 AM EDT Fri Jun 28 2024 .SYNOPSIS... Seasonable temperatures are expected today and tomorrow as shower and thunderstorm activity increases ahead of an approaching cold front. Hot and humid conditions on Sunday will precede the front, which will usher in drier and cooler conditions Monday and Tuesday. The summer heat will return Wednesday and beyond. && .NEAR TERM /THROUGH TONIGHT/... As of 317 AM Friday: Still seeing isolated showers on the KGSP radar in the weak southeasterly upslope low level flow over Upstate SC and northeast GA, altho the biggest concentration has moved off to north central GA. Will maintain a slight chance mostly in the area between I-85 in Upstate SC/northeast GA and the Blue Ridge Escarpment through daybreak. Otherwise, additional low clouds will form through daybreak, which could impact the development of fog in the mtn valleys. Temps will be seasonally mild. Over the next 24 hours, a subtle weakness aloft will linger between the old upper anticyclone over the srn Plains and the reflection of the Atlantic Subtropical High off the Southeast Coast...or maybe what we see in the model guidance is just the result of the moist southeasterly low level flow toward the srn Appalachians. Either way, coverage of showers and storms is expected to be a bit greater this afternoon than the past few days. That being said, expectations are tempered somewhat by our recent lack of widespread rain, and wondering if the models are...a little over-enthusiastic. The precip probs were kept fairly close to the old forecast, but if anything might be overdone. Severe weather chances appear to be low. High temps should stay close to normal. For tonight, the persistence of the weak low level moist flow from the south should support a continued rain chance with a focus on the Blue Ridge Escarpment. Isolated and locally heavy rain would not be a surprise, but confidence is low. Min temps look a bit warmer than normal. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 249 AM EDT Friday: A moist subtropical airmass will continue to advect into the forecast are on Saturday as ill-defined upper flow over the immediate forecast area does little to interact with deep SSE flow at the low levels. Forecast profiles on Saturday appear moist through the depth of the troposphere, especially during the afternoon hours. Operational guidance depicts some 1000-1500 J/kg sbCAPE developing during the afternoon and evening across most of the forecast area...but with anemic lapse rates that should hinder more robust updrafts from developing. And, without much synoptic forcing, it`ll be tough to trigger initiation en masse, which should once again limit convective coverage. So, despite juiced-up PWs exceeding 2" in some areas, the threat of either severe weather or heavy rainfall appears limited. Temperatures Saturday afternoon should climb into the upper 80s or lower 90s along the I-77 corridor. With profiles as moist as they are, any amount of diurnal mixing will do little to lower dewpoints, so afternoon heat index values may surge into the upper 90s...possibly hitting 100 in isolated locations along the southeastern fringe of the forecast area. On Sunday, z500 troughing over the Great Lakes will sharpen, and a shortwave will dig across the central Midwest and Ohio Valley, pushing a surface cold front into the Cumberland Plateau and upper / central Tennessee Valley through afternoon. Oddly, guidance depicts a W wind developing at the low levels Sunday morning in response to a subtle shortwave crossing the region...which will both boost temperatures and lower dewpoints, as well as have an initial suppressive impact on convection east of the mountains where normally the dynamics might support better initiation and stronger updrafts. Instead, the mountains still look like a focus for afternoon showers and thunder...although the Piedmont and Upstate zones should eventually catch up and destabilize despite the transient downsloping effect. Forecast sbCAPE values range from <1000 J/kg in ensemble members that depict a stronger downsloping effect, to over 2000 J/kg in the more aggressive guidance. A dry slot aloft may support some limited downburst threat...but no widespread severe risk is expected. Like Saturday, there will be limited dry air aloft to mix down on Sunday afternoon, so dewpoints will struggle to lower during peak heating. With temperatures expected to soar into low- to mid-90s on Sunday afternoon, and dewpoints ever soupier...wide swaths of the Upstate and Piedmont can expect to see heat index values in excess of 100 degrees, with some potential for values of 104-106 degrees, mostly south of I-85. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 311 AM EDT Friday: By Monday, the cold front should be pulling east of the forecast area and ushering in somewhat cooler and drier air in for the start of the new week. Temperatures on Monday and Tuesday will only climb into the mid/upper 80s...particularly on Tuesday, which will boast an almost CAD-like pattern with high pressure drifting off the New England coast and driving NE flow across the Carolinas. The latest cycle of ensemble guidance has trended away from much active weather on Monday afternoon, depicting a stronger subsidence inversion across most of the area and very limited moisture. So, maintained token PoPs across the southeastern tier and across the mountains, where some widely scattered showers will be possible. Further quiet conditions are expected on Tuesday, with an even more robust subsidence inversion in place. By midweek, temperatures will be on the rise again as high pressure slides off the Atlantic coast and winds turn back around out of the south. Deep ridging will once again develop over the Southeastern CONUS, maintaining suppressed profiles across the western Carolinas...so although some diurnally-driven afternoon showers can`t be ruled out, the case for robust afternoon convection appears weak through the end of the seven day forecast. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: A light southeasterly low level upslope flow has been established across the region, and in response we are seeing some sct/bkn low clouds forming closer to the Escarpment. This has already brought about an MVFR ceiling at least temporarily to the Upstate SC terminals and KAVL, and that will probably continue through the pre-dawn hours. The new guidance is more interested in developing a more widespread MVFR-level ceiling by daybreak across most of the fcst area with the exception of KCLT. Wind will be light and easterly. By late morning, the ceiling should lift/scatter to VFR prevailing. At that point, we should start to destabilize. The 00Z run of the CAMs suggests perhaps a better coverage of showers and storms on Friday afternoon, so all terminals will be getting a PROB30 handle thunderstorms. It is not clear that storms will have dissipated by mid-evening, but will not continue the chances past that time for this issuance. Wind should come around to something more SE. Outlook: Another cold front approaches the area Sunday night, keeping unsettled weather around through early next week. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...MPR NEAR TERM...PM SHORT TERM...MPR LONG TERM...MPR AVIATION...PM