374 FXUS62 KGSP 101557 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1157 AM EDT Wed Oct 10 2018 .SYNOPSIS... A strong upper level ridge will remain over the region and maintain above normal temperatures through Thursday. Moisture levels will increase during this time as tropical cyclone Michael tracks northeast and reaches our forecast area on Thursday. Canadian high pressure will build in Friday and bring seasonably cooler and drier air before a moist cold front reaches the region Sunday night. && .NEAR TERM /THROUGH THURSDAY/... As of 1130 am Wednesday: Latest water vapor imagery depicts a plume of tropical moisture extending from eastern Kentucky/east TN through the North Carolina Piedmont late this morning. A band of widespread moderate to heavy rain associated with this plume continues to impact much of our NC zones (mainly from the Blue Ridge east), while scattered to numerous showers cover much of the southwest 2/3 of the area. Meanwhile, a region of subsidence/mid-level drying is seen between the moist plume and the outer bands of Hurricane Michael. As this subsident region pushes its way across the region during the afternoon, activity should become more showery/less persistent across western NC as well, except perhaps along the eastern Blue Ridge escarpment, where strong upslope flow will likely keep moderate to heavy rain going through the afternoon. Storm total amounts of 1-2 inches have already occurred in these areas (mainly from Lake Lure north), and up to an additional inch appears likely in many areas through the afternoon. We're already seeing some advisory-level hydro issues in these areas, and conditions should only continue to gradually deteriorate through the afternoon/ evening. Some moderate instability is likely to develop this afternoon across the southern half of the forecast area, where breaks in the clouds are more likely in light of the mid-level drying. While shear will be increasing throughout the day, the stronger shear will lag the better instability by several hours. Therefore, there probably isn't much of a severe weather threat this afternoon, but we may see development of discrete thunderstorms that will bear watching. Enter Michael. The storm will be moving into/across southern GA around or shortly after midnight tonight, and all guidance is bringing it in to SC sometime after sunrise Thursday. GFS is a little slower than the NAM and ECMWF but enough consensus there to be reasonably confident. The storm will then push through SC and into NC during the day. 1) QPF. Per WPC guidance, they have shifted the axis of heaviest rain just a tad to the NW. This is concerning for the CLT Metro area, where now our storm totals are now around 5" (vs. 4" this time yesterday), with slightly higher amounts further SE. Most of this falls in the 12z Thu-00z Fri time period. There is still some uncertainty with the axis of heaviest rain but in looking at the larger picture, certainly seems that as Michael interacts with the baroclinic zone set up by the lookalike-damming, we could get something that looks like a deformation axis setting up with some conditional symmetric instability and frontogenetical forcing (think winter weather) that could enhance some banding-like structures. No change of course to the FFA but we could see some hefty amounts in very short periods of time if this comes to fruition, and urban flash flooding in the CLT Metro is an increasing concern. Another note is that new HRRR guidance (HRRE specifically) is quite concerning across the mountains tonight. Probably a little too high (4-8"!) but is concerning enough to mention as a possibility. 2) Winds. Aforementioned interaction between Michael and that baroclinic zone may act to locally strengthen winds due to the sustained (rather than weakening) pressure gradient along the SE portion of our area. After consultation with surrounding offices, opted to go with TR.W for Elbert/Abbeville/Greenwood and TR.A for the rest of our 1st tier of southern counties. We actually have very little expectation that we would actually SEE tropical-storm-force winds, but probabilities are high enough to warrant the issuance. If nothing else, with increasingly saturated soils, some impacts are likely. Hard to tell how far north the stronger gusts will extend at this time but isolated gusts 20-30kt certainly not out of the question anywhere east of the mountains (and of course at the peaks, but that's not unusual). 3) Tornado potential. SPC brought the marginal risk in to our area for Day1, mainly for the overnight period. Deep-layer shear will begin increasing after 00z (the NAM is a little more aggressive with this) and will briefly be collocated with afternoon convective instability (albeit weak, <1000J/kg). Better shear will move in overnight ahead of Michael and naturally instability will decrease through the overnight, but even in the middle of the night (06-09z) looks like we could have a combination of 40-50kt shear with 300- 600J/kg SBCAPE and, as would be expected, increasing low level helicity. The tornado threat is low, especially with our area being on the left side of the track, but ahead of the storm it is certainly non-zero and will continue to advertise a "limited" threat especially through the overnight hours, decreasing through the day on Thursday. That's pretty long, but just to recap the two bigger take-home points: Flash flooding potential remains #1 concern and is actually increasing with latest guidance, and have issued GSP's first-ever tropical wind products (in collaboration with surrounding offices and NHC). && .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY/... As of 230 AM Wed: Michael will depart quickly to the east Thursday night. Most model guidance depicts the precip ending in our far eastern zones by midnight if not sooner. Breezy northwest winds will continue into early Friday as cool and dry high pressure begins to build east. Min temps will be near normal in the mountains; the Piedmont will remain several degrees above normal. Maxes will be about normal on Friday. Though high pressure will continue to dominate the sfc pattern across the Southeast, a fast-moving shortwave will traverse the Ohio Valley Friday night. This looks unlikely to produce any mountain precip, but a period of increased cloud cover may result. The sfc high will center over the region Saturday and return flow will start to develop, though max temps will fall back a category or so below normal. && .LONG TERM /SATURDAY NIGHT THROUGH TUESDAY/... As of 150 AM Wednesday: Starting Saturday evening with cool and dry high pressure centered near West Virginia as it transits to the east. Former TC Sergio which crossed the Baja Peninsula is forecast to be over Texas and Oklahoma Saturday evening. As the next upper trough drops down over the northern plains Saturday night and Sunday, Sergio gets caught up in the flow ahead of this trough. Remnants of Sergio moves across the Tennessee and Ohio Valleys going into the start of the week. The cold front advances toward our area on Sunday and Sunday night as the previous high moves well out over the Atlantic. The GFS is more progressive as on Sunday evening the front extends from the Texas Coast to the eastern Great Lakes while the ECMWF has the front from Dallas to St Louis. The GFS was trending wetter with the south end of Sergio brushing the NC mountains, but the latest run is drier. The EC has Sergio passing over the Ohio Valley Monday while we get very little precip. The more progressive GFS has the front pushing through late Monday with dry high pressure transitioning from west to east north of our region through Tuesday night. The EC delays the high's arrival until Wednesday with a lingering front over our area from Monday until Wednesday. At this point, not making any drastic changes to the forecast until we have a better idea for this time period. Cooler Temperatures are the certainty with Mins a few degrees below normal Saturday night then near normal into first part of the week. Max temps near normal. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... At KCLT and elsewhere: Pretty solid IFR this morning and little improvement expected during the day, though pockets of MVFR certainly not out of the question this afternoon. Occasional -SHRA will continue, and have TEMPO TSRA or VCTS for the Upstate TAFs and KCLT (KAVL and KHKY not confident enough to include in TAFs at this time). Cigs drop again overnight tonight with IFR to LIFR prevailing in more widespread SHRA ahead of Michael. Winds will start out ENE for all but KAVL (where SE down-valley winds will continue) and remain ENE for Upstate TAFs, though KCLT/KHKY should see slight veering more to ESE or even SE by early afternoon (might trend back E late in the period but hard to pin down those details just yet). Speeds close to 10kt today will increase slowly late in the period, with some low-end gusts possible for Upstate TAFs and KCLT Thursday morning continuing into the end of the period. Outlook: Periodic restrictions, heavy rainfall, and some gusty winds are expected through Thursday as tropical cyclone Michael passes over or near the region. Expect improving conditions after Michael exits the area for the end of the week, but restrictions will be possible again early next week as a front approaches the area. Confidence Table... 16-22Z 22-04Z 04-10Z 10-12Z KCLT High 92% High 87% Med 78% High 100% KGSP High 85% High 94% Med 72% Low 58% KAVL High 82% High 94% Med 65% High 100% KHKY High 93% Med 69% High 90% High 91% KGMU High 85% High 87% High 81% Low 58% KAND High 82% High 94% Med 72% 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...Flash Flood Watch from late tonight through Thursday evening for GAZ028-029. Tropical Storm Warning for GAZ029. NC...Flash Flood Watch through Thursday evening for NCZ033-049-050- 053-064-065-501>510. Flash Flood Watch from Thursday morning through Thursday evening for NCZ035>037-056-057-068>072-082. Tropical Storm Warning for NCZ082. SC...Flash Flood Watch from late tonight through Thursday evening for SCZ002-003-005>007-010>013-019. Flash Flood Watch from Thursday morning through Thursday evening for SCZ008-009-014. Tropical Storm Warning for SCZ009-011>014-019. && $$ SYNOPSIS...DEO NEAR TERM...JDL/TDP SHORT TERM...Wimberley LONG TERM...DEO AVIATION...TDP