Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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380 FXUS62 KGSP 080457 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1257 AM EDT Wed May 8 2024 .SYNOPSIS... A summerlike weather pattern lingers through mid-week leading to mainly diurnal showers and thunderstorms and above normal temperatures. Showers and thunderstorm activity will become more numerous ahead of a strong cold front tonight into Thursday, with severe storms possible. The cold front pushes east early Friday morning but another system approaching out of the south may bring shower and thunderstorm chances back again on Friday. Drier conditions and below normal temperatures return just in time for the weekend. && .NEAR TERM /THROUGH TODAY/... As of 100 AM EDT Wednesday: Dry conditions are noted across much of the forecast area this morning, although a few isolated showers have pushed east into extreme NE GA. Widespread upper cloud cover continues to fill in across the forecast area this morning, so this may act to limit fog formation somewhat across the NC mtns and Foothills. Updated PoPs based on the latest radar trends this update, and also tweaked PoPs through the duration of the near term based on the latest CAM guidance. Otherwise, the rest of the overnight should be fairly quiet with only a small collection of showers expected to develop over the mtns and Foothills, with maybe a brief embedded thunderstorm or two. Lows this morning will end up around 15 degrees above climo thanks to cloud cover and SW`ly flow. Upper ridging over the Appalachians will breakdown and shift offshore this afternoon with a highly perturbed southwest flow regime setting up from the Lower Mississippi Valley into the Southern Appalachians. This will keep an active period of weather around through the near term. A residual elevated mixed layer will advect into the area today, acting to keep the atmosphere capped through the early afternoon hours. However, with time, increasing forcing for ascent and surface heating should erode the cap and allow for thunderstorm development. Considerable spread was noted in the high-resolution CAM guidance as to when/where storms will develop. The greatest coverage is expected across the mountains initially with scattered storms into the foothills. As the afternoon progresses, activity will likely spread across much of the area along and north of I-85. The atmosphere will be primed for severe weather with 3000-4000 J/kg of surface-based CAPE, 6.5-7 C/km mid- level lapse rates, and 30-40kts of deep-layer vertical wind shear. This would be supportive of large hail and damaging winds with the wind threat becoming dominant/more widespread should convection organize into linear segments. As such, the expansion of the slight risk from SPC appears warranted. Temperatures this afternoon will be the warmest of the week, with highs climbing into the mid to upper 80s in the mtn valleys and east of the mtns. Areas near the Charlotte Metro may even see highs reach the lower 90s. Thus, highs will remain around 10-13 degrees above climo. && .SHORT TERM /TONIGHT THROUGH FRIDAY/... As of 215 PM EDT Tuesday: CAMs show the potential for a couple of rounds of convection crossing the area Wednesday night. Moderate shear and decent elevated instability could allow some of the storms to become strong to severe. The severe threat could continue into Thursday as another round of convection moves through. Moderate shear is likely, with moderate instability possible, especially if the cap can erode and LFCs become low enough. Any convection that does develop should quickly move east early Thursday evening. The GFS continues to be more aggressive with the next short wave dropping into the area Friday, and the resulting cyclogenesis. It is the wettest guidance, but there is some response from the other guidance. Have gone with the model blend for PoP which favors the mountains and CLT Metro. This is still in the chance range across the entire area. QPF that does fall will be light. Temps will be well above normal Thursday, dropping to around normal Friday. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... As of 155 PM EDT Tuesday: Not much change in the forecast this period with short waves rotating through a low amplitude long wave trough over the eastern CONUS. Weak surface features move over or near the area in association with the short waves through Monday. There may be enough moisture for isolated to low end scattered showers across the mountains, but any QPF will be light with a dry forecast elsewhere. Model differences develop Tuesday with a stronger wave rotating through the upper trough producing cyclogenesis along the Gulf Coast with the resulting low moving south of the area. How far south is the question with a drier, farther south track and wetter, farther north track. Have gone with the guidance blend which has low end chance PoP developing. Temps below normal Saturday slowly rise to slightly above normal by Tuesday. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... At KCLT and elsewhere: Expecting a relatively quiet overnight with residual convective debris cloudiness and a light mostly SW wind. There is the concern that fog could develop across the mtns and near KHKY, and it was indicated in the guidance. Low level moisture remains plentiful, so we include a fog restriction in the predawn hours for KAVL and KHKY, even though a blanket of high level clouds will remain. Today looks like it could be an active day convectively...eventually. Models show some shower development early in the day over the mtns, so a TEMPO was included at KAVL to handle the rain chance and the possible lower fog/ceiling restrictions. Once rid of that, all terminals go VFR prevailing for the rest of the period. Wind will come up from the SW with some possible gusts. Then, we wait. There is much uncertainty as to the coverage and timing of any afternoon convection, so a broad-brushed PROB30 will be employed for thunderstorms in the last six hours of most forecasts. We will evaluate the morning guidance and fine-tune the timing of the best thunderstorm chances the next set of TAFs. Outlook: A cold front will approach out of the west on Thursday before tracking over the terminals Thursday night into early Friday morning. This will lead to better convective chances, as well as restrictions. A system lifting out of the south my increase shower and thunderstorm chances again on Friday, but confidence on this remains low. Drier conditions can be expected this weekend. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...AR NEAR TERM...AR/TW SHORT TERM...RWH LONG TERM...RWH AVIATION...TW