Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
064 FXUS62 KGSP 172356 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 756 PM EDT Thu Jul 17 2025 .SYNOPSIS... Daily thunderstorm chances continue through the upcoming weekend. A few storms could produce damaging wind gusts and localized flash flooding. Hot and humid conditions stick around through the forecast period. && .NEAR TERM /THROUGH FRIDAY/... As of 750 PM EDT Thursday: A strong surface high remains parked over the Atlantic and the western side amplifying, keeping the flux of moisture in place. Off to the north, an area of low pressure moves out to the far NE, which has dragged a very weak frontal boundary into the mountains, which is aiding in slightly more lift for convective development this evening, while coverage has dropped off drastically east of the mountains. All other ingredients remain in place much like the past week. Guidance has PWATs in the 1.75-2.00 inch range and relatively weak steering flow aloft. The potential for training and/or back-building storms continues, posing a continued threat of locally torrential rainfall rates and possible isolated/local flash flooding. Overnight, PoPs decrease quickly, but cannot rule out a pop-up shower or thunderstorm before midnight. For Friday, a surface high migrates east from the central CONUS along with the high over the Atlantic. In between the two highs sits the CWA, allowing for continued moisture advection and the typical diurnally driven convection chances. Again, the higher chances are over the mountains (60-80%) and elsewhere 20-40%. Temperatures remain in the low 90s today but heat up more for Friday. The heat index looks to be a bit more of an issue starting tomorrow. Many locations east of the mountains could see HI values in the 100-104 range, but remains just below Heat Advisory criteria at this time. && .SHORT TERM /FRIDAY NIGHT THROUGH MONDAY/... As of 1245 PM EDT Thursday: A fairly active pattern is expected over the weekend thru Monday, as upper ridge retrogrades slightly to the northern Gulf Coast, and heights fall across the Mid-Atlantic. This will allow a quasi-stationary front to slowly sag southward across the Ohio Valley and Mid-Atlantic. A typical hot and humid air mass in place combined with extra focus for convection near the frontal boundary will result in categorical PoPs in the NC mountains to solid chc PoPs across the I-85 corridor and southeast each day. Generally, PoPs will be the typical diurnal aftn to early evening time frame, but some increase in shear along a "ring of fire" around the upper ridge may support MCS activity making a run for the Southern Appalachians either Sunday or Monday. Confidence is still low on that. There may also be an increasing flash flood threat, as elevated PWATS in the 2-2.25" range will persist across the area thru Monday. The area of most concern will be in the NC mountains near the TN border thanks to the persistent westerly upslope flow. Another concern will be the heat index, as dewpts may not mix out as much ahead of the sagging front, while temps get into the mid 90s across most of the Piedmont. The NBM dewpts may be a tad high, but the latest forecast is for plenty of 105-109 heat indices across the lower Piedmont and the Charlotte area each aftn thru Monday. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... As of 100 PM EDT Thursday: Upper ridging begins to reassert itself from the Lower MS Valley toward the east Tuesday into Wednesday. This will allow drier air to work in from the north and bring PoPs back down closer to climo. Temps will remain above normal, but dewpts should mix out more and bring heat indices back under heat advisory criteria for most of the forecast area. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... At KCLT and elsewhere: Mountain convection has increased in coverage over the past hour in areas west and north of KAVL. This warrants a VCSH at KAVL until late evening. Meanwhile, convection is isolated-at-most across the remainder of the area. Additional isolated convection will be possible near the other TAF sites this evening, but any mention of convection for this evening has been removed from all sites expect KAVL. Otherwise, VFR conditions are forecast at the TAF sites through the period. Areas of mountain valley fog and low stratus are likely around daybreak Friday, but will most likely be confined to the valleys west and north of KAVL. Similar to this morning, can`t rule out a brief period of IFR/lMVFR stratus developing around sunrise Friday, but confidence in this is very low at this time. SW winds of 5-10 kts this evening are expected to give way to lighter winds overnight, before increasing to 5-10 kts again by Fri afternoon. Outlook: Thunderstorm chances each afternoon/evening. Low stratus or fog are possible each morning in mountain/river valleys. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...ARK NEAR TERM...CP/JDL SHORT TERM...ARK LONG TERM...ARK AVIATION...JDL