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Area Forecast Discussion
Issued by NWS Greer, SC
Issued by NWS Greer, SC
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127 FXUS62 KGSP 221400 AFDGSP Area Forecast Discussion National Weather Service Greenville-Spartanburg SC 1000 AM EDT Wed May 22 2024 .SYNOPSIS... Temperatures will remain several degrees above normal each day through Tuesday of next week as humid subtropical air remains over the Southeast. Chances for showers and thunderstorms increase Thursday and will remain higher than normal for this time of year into next week as well. && .NEAR TERM /THROUGH TONIGHT/... As of 946 AM EDT Wednesday: No major changes this morning. Quiet across the area with upper ridging extending from the Gulf Coast up into the Carolinas. Still appears that this is keeping lapse rates subdued and surface conditions dry and clear. Otherwise, a plume of upper-level moisture will cross the area today, as it rides over a ridge axis that remains aligned along the East Coast. While the associated cirrus should thin out at times today, it may be just enough to take the edge off peak daytime heating. This combined with warm mid-level temps from the persistent ridging may result in basically a dry day today. Most of the latest CAMs are dry thru 00z today, except for the HRRR, which develops a few cells in the Northern NC Mountains. Even if some deep convection pops, it will likely be just showers, as diurnal activity the last couple of days had little to no lightning. Otherwise, it should be a warm day, with highs likely a degree or two warmer than yesterday`s readings, around 5 degrees above normal. Tonight, shortwave energy will cross the Mid-South and work to start flattening the upper ridge across the Southeast. This should result in more mid and high clouds streaming in overnight. Guidance shows some convection developing across the TN Valley that will drift toward the NC mountains. However, the activity is not expected to arrive before 12z Thu, and should be weakening as it approaches. Lows will be 7-10 degrees above normal under the increasing clouds and an uptick in dewpts within a weak return flow pattern. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 130 AM Wed: Baroclinic zone will be present across the Ozarks and up the Ohio River Valley on Thursday. This feature will trail the occluding low in northern Ontario and its western end will be reactivated by the incipient low in the northern Plains. Jet streak associated with the northern low and upper trough will promote development of a weak shortwave over the front. This looks to ride over our CWA over the course of the day Thursday, suppressing the upper ridge and allowing decent deep layer lapse rates. The wave may effectively pull the sfc front across the Appalachians, with a weak sfc reflection developing over the Mid-Atlantic coast by Friday morning. Convective activity may start near the TN border late Thu morning, as most guidance depicts early day activity in TN via the wave. The remainder of the area will continue to destabilize diurnally. Shear will be a bit better than usual for late May. Furthermore, airmass modification will bring dewpoints a few degrees warmer. Together these suggest diurnal showers/storms will be above climo and so we will advertise chance to likely PoPs for most of the area. Soundings generally feature dry air around 700 mb and seasonable CAPE values, so a localized damaging wind threat may develop. Enough shear is present to think cells will also be semi-organized and capable of at least marginally severe hail. Activity may propagate into the Piedmont following the shortwave or as a result of westerly storm motion. The Plains low will approach the western Great Lakes on Friday. Another, better defined shortwave will take a similar track out of the Mid-South, helping to induce height falls along with the eastward moving northern system. Once again the shortwave is timed to reach our area near peak heating, but still perhaps late enough to keep storms going into Friday evening across the Piedmont. Slightly better lapse rates suggest higher instability; shear will be similar. Higher PWATs and more CAPE in the hail growth temperature zone suggest severe threat may shift more in favor of hail than wind. Although convection is likely to diminish diurnally and/or as the shortwave moves east of the area, some models indicate that convection along the cold front of the aforementioned low will reach the mountains late Friday night if not Saturday morning, so some PoPs linger all night in our west. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 230 AM Wed: Unsettled weather should continue through the weekend and early next week; not much change from last night`s forecast in that regard. It still appears a broad trough will gradually shift across the CONUS, amplifying as shortwaves move east of the Rockies and induce cyclogenesis. These features then look to phase into a deep Eastern trough by early Wednesday. Through the weekend, the pattern remains fairly ill-defined over our part of the country, and confidence is thus relatively low. The frequency of forcing mechanisms, along with expectation we will remain several degrees above normal for temps each day, suggests PoPs will remain above climo each day of the medium range. The shortwave which will be over our CWA on Friday will drift off the VA/NC coast Saturday morning and appears to spin up a weak sfc low to our east. Meanwhile, low amplitude upper ridging will remain inland over our area. This would suggest suppressed convection for the CWA, although GFS and GDPS output suggests the ridgetop convergence may overcome any subsidence, and then there is the matter of the front which may impinge on the Appalachians Saturday morning as noted in the short term discussion. For now, at least we can say Saturday probably will feature the least shower/tstm coverage. The upper pattern remains progressive and the ridge axis is likely to be to our east by Sunday afternoon. Concurrently, developing Plains cyclone will activate a warm front across the lower OH Valley and reestablish southwest flow over our area, as we come under the periphery of the surrounding upper trough. The track and evolution of this system will have implications for our weather Sunday through Tuesday. There does appear decent model agreement Sunday on sufficient CAPE and shear to expect a severe risk from any storms that do fire, mainly of hail/wind. Monday and particularly Tuesday are a bit more in question as models vary in how fast the upper low evolves and in how soon the cold front reaches our area. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... At KCLT and elsewhere: A little bit of fog and stratus has formed near KAVL, but should clear out within the first hour of the 12z TAF. Otherwise, VFR conditions are expected thru the period. With high pressure holding on today, guidance shows only isolated showers developing along some of the mountain ridges. Coverage is expected to be too sparse to mention at KAVL. The Piedmont is expected to be dry with just fair wx cu forming in the aftn. Winds will be light, picking up to 5-10 kt this aftn out of the S/SW, then becoming light again this evening. Outlook: More numerous showers and thunderstorms, along with associated flight restrictions, will return with a cold front late Thursday into Friday. A more active pattern may persist through early next week. && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...Wimberley NEAR TERM...ARK/MPR SHORT TERM...Wimberley LONG TERM...Wimberley AVIATION...ARK