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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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135 FXUS62 KGSP 130725 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 325 AM EDT Tue Aug 13 2024 .SYNOPSIS... Dry high pressure gradually builds in from the north through Thursday, pushing a stalled front further south of the area. The high will drift east off the East Coast Friday, as a cold front approaches from the west over the weekend. The front will bring a return of better chances of shower and thunderstorms. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Tuesday: Already seeing some scattered showers developing along the Blue Ridge Escarpment and the northern NC Foothills this morning. Coverage is expected to expand through the morning hours while pushing east per the 00Z CAMs. A few isolated thunderstorms cannot be entirely ruled out but instability should remain low through daybreak. Areas in the North Carolina mountains west of the Blue Ridge should see dry conditions prevail through the morning hours. With cloud cover expected to linger (and increase) through daybreak, lows will end up around 2-4 degrees above climo. Cloud cover should limit mountain valley fog formation somewhat but patchy fog may still develop. Otherwise, upper troughing will remain over the Carolinas through the near term while periodic shortwaves track over the region from the northwest. Meanwhile at the sfc, the southern periphery of surface high pressure centered over the Great Lakes region will extend into the Carolinas while a front stalls over the Southeast. This will lead to a more convectively active day compared to yesterday. 00z CAMs show scattered convection firing over the mountains by the early afternoon hours, gradually spreading east through rest of the afternoon and early evening. Although deep shear will range from 35-45 kts today, 00Z HREF ensemble probability shows less than 2,000 J/kg of CAPE across the forecast area through the period. However, the 00Z CAMs show the potential for 1200-1500 J/kg of CAPE across the southern zones during peak heating. The SPC Day 1 Severe Wx Outlook shows a Marginal Risk for isolated severe storms across the eastern SC Upstate and the southern NC Piedmont (south of CLT) today. This looks reasonable as the far southeastern zones have the best chance to see cloud cover breakup briefly this afternoon, allowing for better destabilization. The excessive rainfall concern should remain isolated with higher shear values in place today allowing for faster storm movement. However, flash flood guidance continues to be on the low side (mainly across the eastern two- thirds of the CWA) due to the rainfall from Debby last week and rainfall over the weekend. Convection should gradually end from west to east late this afternoon into this evening, with drier conditions moving in tonight. Temperatures this afternoon will be much cooler compared to yesterday. However, highs will remain a few degrees above climo across the Little TN Valley and the Upper Savannah River Valley. Highs elsewhere should end up a few to several degrees below climo thanks to higher cloud cover. Lows tonight will end up near climo to a few degrees above climo. Patchy fog may develop across the NC mountains and Foothills overnight into daybreak Wednesday. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 145 AM EDT Tuesday: The short term looks fairly quiet, as the axis of a deep upper trough will swing east off the East Coast, and upper ridging builds in from the Lower Mississippi Valley Wednesday thru Thursday. At the sfc, dry air will filter in from the north, limiting instability. A light easterly or southeasterly low-level flow may be enough to force a few isolated showers and perhaps a garden-variety tstm or two Wednesday and Thursday aftns in the mountains, but otherwise, it should be partly cloudy with temps slightly below normal. Highs in the mountain valleys and Piedmont will be mainly in the low to mid 80s and lows in the mid to upper 60s. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 230 AM Tuesday...The medium range guidance is in good agreement on a vigorous shortwave diving thru the western Great Lakes Friday, carving out a fairly deep upper trough across the Ohio Valley Saturday, then persisting as a long wave trough across the eastern CONUS into early next week. An associated low pressure system will bring a cold front into the Ohio Valley and possibly crossing the forecast area over the weekend. The front is expected to stall out roughly across the Midlands or Coastal Plain Sunday or Monday. Overall, the front will have limited moisture to work with, but should support scattered to numerous showers and thunderstorms in the NC mountains with help of NWLY upslope flow Friday and Saturday. Downsloping east of the mountains may limit coverage, but support a return of near-normal to slightly above-normal temps. Drier air filters in behind the front Sunday into Monday, lowering PoPs and bringing temps down a couple degrees. && .AVIATION /08Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: 06Z TAF period will be rather active as CAMs show the potential for scattered convection developing in the next few hours and lingering through potentially mid-morning. Thus have TEMPOs for -SHRA through the morning hours east of the mountains. KAVL will likely stay dry through daybreak but have a TEMPO for MVFR cigs and fog around daybreak. KHKY could see IFR cigs develop by mid- morning so have this accounted for in a TEMPO. Elsewhere generally MVFR to VFR cigs and vsbys are expected through the period outside of convection. Scattered showers and thunderstorms are expected to develop this afternoon and evening so have PROB30s for -TSRA at all terminals to account for this activity. Wind direction will remain N/NE east of the mountains through the TAF period. Winds at KAVL will be calm to light NW through daybreak before turning more E/NE. Outlook: Expect mostly diurnal isolated to scattered diurnal convection through Thursday. Coverage of convection increases Friday into Saturday as a cold front approaches out of the west. Patchy fog and low stratus will be possible each night in the mountain valleys and in any locations that received heavy rainfall the day prior. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...ARK NEAR TERM...AR SHORT TERM...ARK LONG TERM...ARK AVIATION...AR