Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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996 FXUS62 KGSP 260806 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 406 AM EDT Thu Sep 26 2024 .SYNOPSIS... Tropical Cyclone Helene is forecast to make landfall over the Florida Panhandle late today. The remnant circulation will move quickly north through Georgia bringing continued heavy rainfall, significant flooding and strong winds tonight into Friday morning. Expect a calmer weekend with temperatures near seasonal normals. && .NEAR TERM /THROUGH FRIDAY/... As of 3:45 am Thursday: ***A MAJOR RAINFALL EVENT FOR THE SOUTHERN APPALACHIANS AND VICINITY WITH THE POTENTIAL FOR WIDESPREAD TO CATASTROPHIC FLASH FLOODING IS OCCURRING*** A wide band of moderate to heavy showers continues to stream north- ward within a plume of deep tropical moisture to the east of a stalled frontal bndy still over eastern TN. Thus, the Predecessor Rain Event (PRE) continues with a handful of Flash Flood Warnings having been issued since midnight. We have not seen much if any lightning over our area over the past few hrs, but the I-77 corridor still appears to have upwards of 500 J/kg of sfc-based CAPE and deep layer shear of 30 to 40 kt. Thus, another brief tornado remains possible going forward. Nonetheless, the flash flood threat contin- ues to increase as the rain continues to fall, mainly over the foothills and along/near the Blue Ridge Escarpment. Another broad area of heavier rain is currently approaching our area from the south within this moist conveyor belt. This rain will likely put more streams into flood thru the early morning hrs. Otherwise, no changes were made to the Tropical Storm Warning or the Flood Watch with this fcst update. The latest CAMs are still suggesting that a swath of stronger wind gusts will spread over our area just after 00z Friday and continue thru the morning. They should start weakening by the afternoon, but conditions will remain gusty thru the evening. Otherwise, all signs point to a significant tropical event across the western Carolinas and northeast Georgia. Helene will be a large and fast-moving storm, so any additional minor shifts in the storm track probably won`t change much at this point. We still expect a rare and significant amount of rainfall over much of our mountains and adjacent zones with damaging to catastrophic flooding likely. In the past, once the rainfall gets above roughly ten inches, we have seen numerous reports of land- slides across the high terrain. If you live in these areas, it is imperative that you take whatever precautions you can now, as the flood/landslide threat will continue to increase today and tonight. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... As of 245 am EDT Wednesday: Calm weather will return to the CWA by Friday night, as the center of Helen will be spinning down over the western Ohio Valley...with only some spotty showers expected to linger across the mountains. Winds will remain gusty Fri evening... albeit well below any Wind Advisory criteria...but will gradually diminish through the night. With upper low remaining virtually stationary across the TN/OH Valley, spokes of vorticity lifting south of the low will approach the southern Appalachians Saturday into Saturday night. This is expected to induce scattered shower development...with perhaps a thunderstorm or two...mainly Saturday afternoon/evening. Can`t rule out some locally heavy rainfall within any of this activity, but any precipitation should mostly be light. Temperatures will be right around normal through the period. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 200 am EDT Thursday: Global model guidance is not in the greatest agreement regarding the details of the evolution in the upper pattern. However, as a strong short wave trough dips into the northern Great Plains, the general idea is that the upper low... centered somewhere over the Ohio Valley at the start of the extended...will begin to wobble across the Mid-Atlantic and evolve into an open wave at some point early next week. Scattered, mainly diurnal convection (primarily showers) will be possible across the forecast area each day from Sunday through Tuesday...with chances becoming increasingly confined to the mountains later in the period, as the pattern transitions to more of a NW flow regime in the wake of the departing trough. Although precip chances are in the forecast for much of the period, any rainfall is expected to be light. Temperatures are forecast to be very close to climo through the period. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... At KCLT and elsewhere: The main band of rain has spread somewhat further east and now covers more than half the fcst area with most terminals reporting MVFR cigs at this time. Unfortunately, the worst is yet to come. We could see a few lightning strikes embedded in the heavier showers thru the overnight with cigs eventually dropping to IFR as more upslope forcing arrives and the deeper tropical moisture streams up from the south. Once there, terminals should stay down in the LIFR/IFR range for the rest of the taf period. Expect fre- quent heavier showers to move thru the area with winds becoming gusty from the SE after daybreak. Winds and gusts will continue to strengthen later tonight and into Friday. Outlook: TC Helene will bring widespread low cigs, heavy rain, strong winds, and low-lvl wind shear thru Friday morning before moving out of the area late Friday into Saturday. Isolated to sct mainly diurnal convection will be possible thru the weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...Flood Watch through Friday afternoon for GAZ010-017-018-026- 028-029. Tropical Storm Warning for GAZ010-017-018-026-028-029. NC...Flood Watch through Friday afternoon for NCZ033-035-048>053- 056-058-059-062>065-068-069-501>510. Tropical Storm Warning for NCZ033-048>053-056-058-059-062>065- 068>071-082-501>510. SC...Flood Watch through Friday afternoon for SCZ008-010>013-019- 101>109. Tropical Storm Warning for SCZ008>014-019-101>109. && $$ SYNOPSIS...JDL NEAR TERM...JPT SHORT TERM...JDL LONG TERM...JDL AVIATION...JPT