410 FXUS62 KGSP 110741 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 341 AM EDT Thu Oct 11 2018 .SYNOPSIS... Heavy rain associated with Tropical Storm Michael will continue into this afternoon, tapering off as the storm moves east. Gusty winds will persist into Friday morning. Cool high pressure will then settle over the area, bringing seasonably cooler and drier air into the region through the weekend. A cold front will impact the area early next week with a chance of showers. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM EDT Thursday: This has been a particularly difficult forecast, compounded by the effects of the combination of Michael and the incoming front. Luckily, most of the impacts will be out of our area by this evening, but we still have to get through the day first. Rather than bore everyone with the synoptic details that most folks are likely well aware of, will just detail the impacts. 1) Rain. We are seeing some signals in the hi-res models of some incredibly high rainfall rates, 3-4" per hour later this morning. After discussion with WPC, QPF totals have increased today and they introduced a High Risk of Excessive Rain that includes the CLT Metro, and they expanded the Moderate Risk farther west into the NC mountains. The heavy rain remains our #1 concern, and our QPF from now through 00z tonight is upwards of 4-5" across the I-77/I-85 corridor, with widespread 3"+ across most of the Piedmont (this all in addition to what fell yesterday, which is more of a concern over the mountains). 2) Tornado threat. We're seeing this materialize now with enhanced signatures coming into the Upstate. Mesoanalysis only has about 500J/kg CAPE but shear is really over the top with 0-1km SRH of >300m2/s2 moving into the Upstate, and effective bulk shear of 45- 50kt. HRRR keeps this cellular-looking band fairly intact as it lifts north across the area and expect the low-end tornado threat to continue. 3) Winds. This is the toughie. We're seeing some stronger upper winds mixing down in the heavy rain as it is, and as Michael interacts with both the incoming front and the pressure gradient already in place from the little damming look-like wedge feature, every bit of hires guidance is indicating a local increase in winds on the back side of the precip shield across the Piedmont (and possibly even into the mountains with the stronger LLJ, 50kt at 850mb across the mountains). In fact, it may be that some areas from a GSP-Statesville/Salisbury line actually see *stronger* winds than our extreme southern counties (that will be closer to the center of the storm). Of specific concern is the HRRR, while perhaps overdone, which gives upwards of 50kt gusts spreading across the Piedmont from the western Upstate this morning toward the I-77 corridor early this afternoon. Messaging this is difficult because TS probs from NHC actually *decreased* with the 11p advisory, but they take into account really only the immediate sustained wind radii associated with the wind ball itself and not necessarily any extratropical elements *OR* the gusts. Additionally, the gradient winds over the mountains (Balsams, Blacks, and points north - not Smokies) will be just as strong as winds in the Piedmont, with possibly higher gusts from that LLJ. With this, without having a better option (we are prevented from issuing a Wind Advisory or High Wind Warning if there are Tropical headlines in effect), have opted to expand the TR.W across a good chunk of the area. We know this is a very short-fused lead time and is likely confusing and maybe not even the best option, but given the saturated soils and potential impacts (there will certainly be trees down), feel this is the prudent action. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 130 AM Thu: Surface high pressure will filter into the Southeast Friday bringing a dry northwesterly flow across the CWFA and the return of temps very close to normal. However, a fast-moving shortwave will move all the way from the central Plains to New England between Friday afternoon and Saturday afternoon, with a cold front in tow. While the best lift will be north of our area, a brief chance of precip will accompany these features as they cross the mountains early Saturday. Another, cooler sfc high will move in behind the front, bringing temperatures a little below climo for Saturday afternoon. This front will weaken and stall across the Southeast Saturday night. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 230 AM Thu: Southerly low-level flow already should be underway at the start of the period Sunday morning. Clouds and precip chances will increase Sunday into Monday, as the Southeast remains in a warm-sector pattern under a building upper ridge, with a nearly stationary frontal boundary stretching across the Ozarks and and Ohio Valley. Some SBCAPE even is progged to return to the area Monday afternoon, bringing thunder chances, but looking too small to support much severe threat. Temps will briefly rise a category or so above normal again. Some PoP will linger through Tuesday with timing differences in how fast the front lifts north away from the region, if at all, and with afternoon instability possibly returning. A full-latitude upper trough will advance through the middle of the CONUS Tuesday afternoon and night, driving the boundary back through our area once again as a cold front. In the wake of that front, PoPs finally taper off, and still cooler air pushes in. Temps look to fall back to or slightly below normal again by the end of the period. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... At KCLT and elsewhere: Widespread IFR across the area at TAF time will see little improvement until later this morning. SHRA overspreading the Upstate and will continue to lift north. Cannot rule out isolated thunder but not enough to include in TAFs at this time. Should see rapid clearing from the W generally starting around or just after 18z with cigs lifting through MVFR and to VFR by this evening. Winds will also be on the increase out of the E through the early morning hours with pretty steady gusts to 30kt or thereabouts today with continued LLWS concerns, but as the center of Michael passes to our south today, winds will shift rapidly N to NNW. Winds will diminish after midnight for all but KAVL, where 20-25kt gusts will continue through the end of the period. Outlook: Fair conditions develop for the weekend, but restrictions will be possible again early next week as a cold front approaches the area. Confidence Table... 07-13Z 13-19Z 19-01Z 01-06Z KCLT High 86% Med 70% High 90% High 100% KGSP Med 62% Med 61% High 100% High 100% KAVL Med 66% High 82% High 97% High 100% KHKY Med 63% Med 74% High 96% High 100% KGMU Low 59% Med 71% High 100% High 100% KAND Med 73% Med 78% High 100% High 100% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: www.weather.gov/gsp/aviation && .GSP WATCHES/WARNINGS/ADVISORIES... GA...Tropical Storm Warning for GAZ028-029. Flash Flood Watch through this evening for GAZ028-029. NC...Tropical Storm Warning for NCZ033-035>037-049-050-052-053-056- 057-059-063>065-068>072-082-501>510. Flash Flood Watch through this evening for NCZ033-049-050-053- 064-065-501>510. Flash Flood Watch through this evening for NCZ035>037-056-057- 068>072-082. SC...Tropical Storm Warning for SCZ001>014-019. Flash Flood Watch through this evening for SCZ002-003-005>007- 010>013-019. Flash Flood Watch through this evening for SCZ008-009-014. && $$ SYNOPSIS...Wimberley NEAR TERM...TDP SHORT TERM...Wimberley LONG TERM...DEO/Wimberley AVIATION...TDP