... A weak cold front will move south across our area tonight and Tuesday. This will result in scattered to numerous showers and thunderstorms with a few locations getting excessive rainfall in a short time. Expect drier and hotter conditions Wednesday through Friday with high temperatures feeling like 100 degrees in the piedmont. A weak cold front will drop south this weekend cooling temperatures to near normal.
NEAR TERM /THROUGH TONIGHT/... As of 1035 am: The region is already becoming unstable this morning, with a small amount of vertical shear growing in the convective layer. Upper heights will fall slightly across the entire Southeast through the near term, as a series of speed maxima pass through the Mid-Atlantic and northeast. An associated weak cold frontal zone will sag into our North Carolina zones by the end of the day, and this will act upon a moderately unstable air mass to focus scattered to numerous convective coverage...first across the mountains and I-40 corridor by the early-afternoon, progressing to the I-85 corridor during mid- to late-afternoon and early evening. PoPs are advertised in the 60-70% range in this area prior to 00Z Tuesday. With the faster mid-level flow expected to remain north of the forecast area, wind shear will remain weak, but the degree of instability (SBCAPE in excess of 2500 J/kg in many areas) combined with the volume of storms will likely yield a handful of pulse severe storms. Meanwhile, forecast wind profiles remain supportive of slow-moving and back-building cells. With warm cloud depths forecast to be AOA 11 kft through the period, there is expected to be a bit of an uptick in the potential for locally excessive rainfall/flash flooding, warranting the upgrade to a slight risk in WPC's Excessive Rainfall Outlook...mainly across western NC, with the latest Outlook encompassing the rest of the CWA in a marginal risk.
Convective coverage is expected to diminish this evening, but with the weak boundary remaining in the area and conditions remaining very moist...with moderate instability likely persisting...some degree of isolated/scattered coverage will likely continue through the overnight, with a diminishing, albeit non-zero threat for localized flash flooding continuing. Temps will be a couple of degrees above normal through the period.
SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM EDT Monday: No major changes to the overall synoptic pattern. The ridge of high pressure will continue to dominate across the western and central CONUS while a trough digs south across the New England and the Mid-Atlantic states. The southeastern periphery of this ridge out west is still expected to gradually nudge eastward Wednesday into Wednesday night.
At the sfc, the cold front associated with the upper-level trough should be draped across the southern and eastern tier of the CWA early Tuesday. This allows moisture to linger across the western Carolinas and northeast Georgia with PWATs ranging from 1.50 to 1.90 inches across the mountains and 1.90 to 2.50 inches across the North Carolina Foothills and Piedmont, and the South Carolina Upstate. These PWAT values combined with efficient warm cloud processes will lead to the potential for isolated flooding or flash flooding again on Tuesday. Areas that received heavy rainfall the last few days as well as locations that repeatedly receive heavy downpours are the most susceptible. WPC currently has the entire CWA in a marginal risk on Tuesday for excessive rainfall. PoPs will increase throughout the day becoming likely by Tuesday afternoon and evening with widespread showers and thunderstorms tracking across the CWA. Although the potential for flooding or flash flooding looks to be the main concern with this frontal boundary, there is some potential for isolated severe wx as instability will be present. GFS model soundings show SBCAPE values ranging from 1000 to 1500 J/kg across the mountains and NC Piedmont and 1500 to 2000 J/kg across the SC Upstate. The Canadian and ECMWF seem to be in agreement with these SBCAPE values. However, NAM model soundings are on the higher end with SBCAPE values ranging from 1500 to 2000 J/kg across the mountains and NC Piedmont and 2500+ J/kg across the SC Upstate. All global models are in good agreement that the 0-6 km bulk shear should range from 15 to 25 kts. Therefore, cannot rule out isolated strong to severe storms Tuesday with the main potential impact being isolated damaging wind gusts. SPC keeps the entire area in a general thunderstorm risk for Tuesday. The cold front should weaken and eventually dissipate late Tuesday allowing PWATs to gradually decrease across the CWA late Tuesday night into early Wednesday. As a result, shower and thunderstorms should gradually taper off from west to east Tuesday evening into Wednesday morning. Tuesday's highs should be slightly cooler compared to Monday thanks to northerly flow behind the FROPA.
Wednesday should be dry as the ridge of high pressure nudges westward into the Southeastern CONUS. Kept a slight chance for isolated showers and thunderstorms for the extreme southeastern zones as the GFS and ECMWF were hinting at activity in that vicinity. Confidence on this occurring is very low as the extension of the ridge of high pressure should lead to subsidence across the region. Otherwise, Wednesday will be noticeably hotter compared to Tuesday thanks to the SW periphery of the ridge over the area. Heat indices could reach the triple digits across the extreme southern tier of the SC Upstate and NE GA.
LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 AM EDT Monday: The overall synoptic pattern remains the same into late this week with troughing across the Northeastern United States and a ridge across the central and western US. Late this weekend into early next week this high pressure ridge should gradually breakdown across the western US, building across the southern US while troughing remains over much of the Northeast.
The ridge of high pressure across much of the CONUS will continue to extend across the CWA Thursday before retreating west Friday. This will lead to continued dry and hot conditions Thursday. Heat indices could reach the triple digits again on Thursday and Friday. This looks most likely across the far southern and southeastern zones.
A cold front drops out of the OH Valley Thursday tracking into the CWA Friday into Saturday leading to increased shower and thunderstorm chances. This front has the potential to stall across the area Sunday. Forecast confidence remains low at this time due to model disagreement on the timing and placement of the QPF. Therefore, have kept only a slight chance to chance for PoPs this weekend. Early next week another cold front looks to drop out of the OH valley tracking into NE GA and the western Carolinas brining yet another chance for showers and thunderstorm. Capped PoPs at chance for now due to model disagreement as well as this FROPA occurring towards the end of the extended forecast period. High temps should be noticeably cooler this weekend into early next week compared to Thursday and Friday.