... Hot and humid high pressure will linger atop the region through the end of the week with typical daily mainly afternoon and evening thunderstorm chances. High pressure breaks down and retreats west as a cold front approaches from the north this weekend, making for a showery but cooler weekend and start to next week.
NEAR TERM /THROUGH WEDNESDAY/... As of 2pm EDT Tuesday: Moderate ridge over the southeast half of the CONUS with northwesterly flow aloft over GSP, changes little in the near term, as does the warm, moist airmass parked over the GSP area; continuing chances for afternoon thunder this afternoon and tomorrow. Upper shortwave well north of the area that extends into Canada, swings across the northeast CONUS on Wednesday, with a related surface trough that will weakly extend down into the southeast CONUS and across the GSP CWA. This feature enhances dynamical forcing for thunderstorms Wednesday afternoon, and a step- up in intensity and number of storms is anticipated, leading to the SPC SLIGHT risk category for much of the area on Wed. Deep shear will be weak both today and tomorrow, and the main threat from the strongest storms will be from wind in storm outflows. Surface winds will be fairly steady southeasterly today and tomorrow, except in the mountains on the west side of the surface trough on Wednesday where winds may be come weak northwesterly for awhile. This will support continued high levels of moisture with minimum dewpoints in the low 70s, and continued heat, with highs into the 90s. Afternoon heat index levels approach 105F Wednesday afternoon, which is close to that needed for a Heat Advisory, but there is some uncertainty as to how much clouds and rain will affect the highs. PWAT levels are also elevated, topping 2". Showers that do form could produce enough rain to cause localized flooding, especially considering the weak steering winds.
SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... As of 1205 PM EDT Tuesday: Close to a persistence fcst with only nominal changes from the going thinking with respect to the sensible wx fcst Thursday and Friday. The cwfa will linger within the northern periphery of a strong e-w oriented southern CONUS anti- cyclone. The mean WNW llvl flow will aid in boosting piedmont maximum temperatures about 5 deg F above climo each afternoon, and as long as the sfc dwpts don't downward mix a great deal, piedmont heat index values should reach into the lower 100s. Ripples of energy remain progged to rotate through the region within the weak WNW flow aloft to provide additional potential triggering mechanisms. In conjunction with possible lee troughing and terrain impacts, daily deep convective coverage should become numerous each day, especially within the less suppressed regime and slightly better flow acrs w NC. Given this enhanced mean flow and potentially strong SBCape values expected, a smattering of severe thunderstorms are probable each day.
LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... As of 1230 PM EDT Tuesday: Heading into the weekend, the southern CONUS upper ridge axis will continue to get suppressed south and west, with a deeper upper trough developing in the east. The cwfa will be coming under the cyclonic flow aloft within the southern periphery of said trough Saturday and Sunday. At the sfc, a southward progressing baroclinic zone will act as a trigger for numerous showers and thunderstorms on Saturday before ushering in noticely less warm temperatures for Sunday, hopefully seeing max temperatures 5 or more degrees below climo. It is possible that a mostly suppressed continental airmass will linger atop the region through Monday before a return to more typical July heat and storminess on Tuesday.