Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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165 FXUS62 KGSP 071719 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 119 PM EDT Tue May 7 2024 .SYNOPSIS... A summerlike weather pattern lingers through mid-week with mainly afternoon and evening showers and thunderstorms expected. Temperatures will trend well above normal through Thursday. Showers and thunderstorms will become more numerous ahead of a strong cold front on Thursday. Activity may linger through early Friday as the cold front pushes east of the western Carolinas. Drier conditions and below normal temperatures return for the weekend as high pressure builds in from the west. && .NEAR TERM /THROUGH TONIGHT/... As of 118 PM EDT Tuesday: No changes necessary with this brief forecast update. Otherwise, a weak upper shortwave trough will finally push east of the forecast area by mid-morning. Drier conditions are now in place across most of the forecast area, but some a line of showers continues across the northern NC zones. Patchy fog and low stratus have developed across portions of the area thanks to widespread convection last night. Fog and low stratus should lift shortly after daybreak. Lows this morning will end up around 10 degrees above climo thanks to lingering low clouds. upper ridging will build across the Southeast today leading to much warmer temperatures as well as lower coverage of diurnal convection. Temperatures this afternoon will climb into the lower 80s in the mtn valleys and the mid to upper 80s east of the mtns. This will yield highs around 8-10 degrees above climo. CAMs agree that isolated storms will develop mid to late afternoon across the NC mtns and Foothills before pushing east into the NC Piedmont late this afternoon into early this evening. With the rest of the forecast area expected to remain dry, went with chance PoPs across western NC for today. The SPC Day 1 Severe Wx Outlook shows a Marginal Risk for isolated severe storms across western NC today. This make sense as 25-35 kts of deep shear and up to 2,500 J/kg of SBCAPE will be in place this afternoon, allowing for severe storm development. Large hail and damaging wind gusts will be the main hazards with any severe storms that develop. Any lingering convection this evening should quickly wane around sunset with the loss of daytime heating. Another round of overnight convection may develop as a cold front slowly approaches out of the west. However, with CAMs not in agreement on shower and thunderstorm activity, confidence will remain very low regarding tonight`s PoPs. Lows tonight should end up around 13-15 degrees above climo, especially if cloud cover and convection manage to develop. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 305 am EDT Tuesday: Convection may be ongoing at the start of the short term...and in fact the highest PoPs for Wed will be in the morning. An elevated mixed layer is forecast to advect into the area from the southwest during the afternoon/evening. This will act to impressively steepen mid-level lapse rates...to the tune of 7.5 C/ km. However, it will also act to cap the atmosphere, as forecast soundings depict a strengthening inversion between 5 and 7 kft. As a result, most model guidance...in particular the convection-allowing models...have very little in the way of a convective response across our area Wed PM. Having said that, the afternoon air mass will actually become quite volatile due to the cooling aloft and strong insolation/hot boundary layer (max temps of around 90 across much of the Piedmont), with sbCAPE of around 3000 J/kg expected during mid/late afternoon. If a couple of cells are able to initiate in this environment...perhaps before capping becomes too strong during mid-afternoon...they are likely to become strong-to-severe, with deep layer shear of ~35 kts suggesting good potential for supercellular structures. If anything, forecast soundings indicate stronger capping Wed night into early Thu. However, convection originating from the very unstable and strongly sheared pre-frontal environment to our west could certainly make a run toward our western areas at any point during this time frame. Convective chances then ramp up across our area during the daylight hours Thursday as frontal zone pushes in from the west...most likely during peak heating. The forecast is somewhat muddled due to the potential for early day convection cooling/stabilizing the atmosphere...at the very least, more in the way of cloud cover is expected on Thu that will act to somewhat inhibit heating/destabilization. However, while the cap is forecast to be eliminated by the daylight hours Thu, a remnant elevated mixed layer regime is still expected to result in rather steep mid-level lapse rates, so it won`t take a great deal of heating to yield at least moderate levels of sbCAPE during the afternoon. Shear parameters will only continue to improve, with 0-6km bulk shear of 40-45 kts expected. Westerly/quasi-boundary-normal shear vectors once again suggest the potential for supercell structures and perhaps smaller linear segments...with low level shear parameters being adequate for perhaps a couple of tornadoes in addition to large hail and damaging downbursts. Convection is expected to come to quick end Thu evening as a drier air mass advects into the area in the wake of the front. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 330 am EDT Tuesday: The 00Z GFS is an outlier in its depiction of a potent short wave trough digging into the TN Valley and southern Appalachians on Friday (other guidance is considerably farther north). As a result of this, the GFS solution would have a surface wave develop across the baroclinic zone across the Deep South, with additional rounds of convection making a run for our forecast area during the day Fri. Again, this is an outlier, but there`s enough a signal in deterministic and ensemble guidance to include chance PoPs during the day. The remainder of the extended should be cooler and much drier as a long wave trough becomes established across the East. Surface dewpoints in the 40s...possibly in the 30s across the mountains will result in wide diurnal temperature ranges...with below normal min temps and near-to- slightly-above normal highs through the period. && .AVIATION /17Z TUESDAY THROUGH SATURDAY/... At KCLT and elsewhere: Afternoon cumulus field will continue to build across the area over the next several hours. A few isolated to scattered showers and thunderstorms will be possible across the mountains and foothills (KAVL/KHKY) with lesser confidence towards KCLT. Mainly quiet conditions are expected overnight, but a batch of showers could bring restrictions to KAVL/KGSP/KGMU during the predawn hours. Thereafter, another afternoon cumulus field is expected along with increasing coverage of showers and thunderstorms by the afternoon. Confidence as to when/where thunderstorms may be tomorrow afternoon is too low to warrant mention in the TAFs just yet. Otherwise, generally light winds are expected out of the west/southwest. Outlook: A cold front will approach out of the west on Thursday before tracking over the terminals Thursday night into Friday morning. This will lead to better convective chances, as well as restrictions, towards the end of the workweek. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...AR NEAR TERM...AR/TW SHORT TERM...JDL LONG TERM...JDL AVIATION...TW