Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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971 FXUS62 KGSP 211042 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 642 AM EDT Fri Jun 21 2024 .SYNOPSIS... Strong high pressure and relatively dry easterly winds should keep the weather quiet and humidity on the low side for today. More humid subtropical air will return Saturday and remain into early next week, resulting in more typical summertime shower and thunderstorm activity, as heat builds over the region. && .NEAR TERM /THROUGH TONIGHT/... As of 630 AM: No major changes this cycle, as far as the near term. Deep upper anticyclone still expected to retrograde slightly through early Saturday morning. Sfc high will remain more or less in the same position off the East Coast but will weaken a little. PBL winds will remain quite weak this morning so even with mixing winds look minimal. Winds will pick up more in the aftn and veer slightly to SE with the retrogression of the upper high and perhaps via the diminished offshore high. Moisture flux remains poor thru the afternoon and dewpoints should mix out a little bit. Thus, despite temps warming another two or three degrees above Thursday`s readings, subsidence aloft again should cap off deep convection even over the ridgetops; only shallow convective noise on CAM output. Flow will remain weak tonight although the fetch becoming more southeasterly, maritime air looks to make more of a run into the area from the SC coast, resulting in a muggier night tonight and a few pockets of low stratus may develop southeast of I-85 by daybreak Sat. Deeper moisture associated with disturbance off the GA coast is expected to remain south of our area. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Key Messages: 1) Warming Trend and Above Normal Temperatures Continue into the Weekend 2) Heat Indices Should Reach the Upper 90s/Lower 100s East of the Mountains Each Afternoon 3) Thunderstorm Chances Return for the Weekend As of 230 AM EDT Friday: Upper anticyclone will continue retrograding westward on Saturday, ending up centered over Texas by the overnight hours on Saturday. The upper anticyclone will remain over the Southern Plains and Desert Southwest through the rest of the short term forecast period. Meanwhile, an upper trough will dig across the East Coast and into the Carolinas Sunday into Sunday night. At the sfc, high pressure will remain in place through Saturday night while a cold front tracks across the Midwest. Diurnal showers and thunderstorm chances are expected to return across the mountains on Saturday but capped PoPs to chance (15%-25%) for now per the latest CAMs showing only isolated activity. The cold front will continue to approach from the north Sunday into Sunday night, allowing shower and thunderstorm chances to increase in coverage ahead of the main FROPA. Thus, have slightly higher chance PoPs (25%- 45%) in place across most of the area during this timeframe. Temperatures will continue on a warming trend through the period and will remain around 5-9 degrees above climo. Heat indices each afternoon should climb into the upper 90s/lower 100s near the I-77 Corridor and in the Upper Savannah River Valley. && .LONG TERM /MONDAY THROUGH THURSDAY/... Key Messages: 1) Heat Indices May Climb Near Heat Advisory Criteria Monday Afternoon for Some Locations East of the Mountains 2) The Lower to Mid 90s Stick Around East of the Mountains Through Wednesday, with Slightly Cooler Temperatures Possible on Thursday 3) Thunderstorm Chances Linger Through Most of the Workweek As of 300 AM EDT Friday: Upper troughing lingers over the area through Monday night before upper ridging builds in late Monday night into Tuesday night. At the sfc, a cold front will track across the western Carolinas on Monday before stalling just south of the area Tuesday into Tuesday night. This will keep shower and thunderstorm chances around, mainly during the daytime Monday. Thus, have chance PoPs (28%-50%) area-wide on Monday to account for the FROPA. Sfc high pressure will build in behind the departing front Monday night into Tuesday night leading to drier conditions per the latest global model guidance. Did hang on to some low-end chance PoPs (25% or less) Monday night into Tuesday night, but these will likely need to be lowered (or even removed) in future updates if the current dry trend holds. Temperatures will remain around 6-9 degrees above climo through the period, with highs climbing into the low to upper 90s each afternoon. Heat indices may reach near Heat Advisory Criteria in the Upper Savannah River Valley and in the Charlotte Metro area Monday afternoon. Heat indices should end up slightly lower Tuesday afternoon thanks to lower dew points behind the cold front. Another upper trough will approach out of the west on Wednesday before tracking across the forecast area on Thursday. At the sfc, another cold front will approach out of the Midwest on Wednesday before tracking across the forecast area on Thursday. This will bring shower and thunderstorm chances back to the forecast area Wednesday into Thursday. Thus, have chance PoPs (30%-50%) area-wide during this timeframe. Highs will remain in the mid 90s again Wednesday afternoon, with heat indices climbing back into the upper 90s/lower 100s along the I-77 Corridor and in the Upper Savannah River Valley. We may finally see some relief from the mid 90s on Thursday, thanks to the cold front and its convection. Highs on Thursday are currently expected to only climb into the upper 80s and lower 90s east of the mountains. Unfortunately this is not too much of a relief from the heat, but it will be welcome nonetheless. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: VFR this morning aside from some fog in the more rural mountain valleys. At issuance time KAVL is reporting an RVR group with 1F dewpt depression so brief/variable IFR fog might occur in the first hour. Winds generally very light and VRB but favoring NE at times before noon. With flow lacking even above the PBL speeds will remain very weak even after mixing begins. As high pressure retrogrades slightly this aftn and especially tonight, however, winds will favor the SE quadrant. Diurnal cu may develop as low as 040 but more likely in the 050-060 range but chance of SHRA still much too low to mention anywhere. The SE winds tonight could allow low stratus to creep in very late, warranting a FEW mention at low VFR level at KCLT. Outlook: Isolated diurnal convection will be possible over the mtns on Saturday, with a return to more sct convection expected across the region Sunday and Monday. Slight drying may follow for Tuesday. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...Wimberley NEAR TERM...Wimberley SHORT TERM...AR LONG TERM...AR AVIATION...Wimberley