textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12z TAF issuance.

KEY MESSAGES

1. A few severe thunderstorms are possible today and Tuesday, mainly in the late afternoon and early evening. The primary concerns from any stronger storms will be damaging wind gusts and excessive rainfall. 2. A cool-down is expected by mid-week that should keep temperatures below normal through the weekend.

DISCUSSION

Key message 1: A few severe thunderstorms are possible today and Tuesday, mainly in the late afternoon and early evening. The primary concerns from any stronger storms will be damaging wind gusts and excessive rainfall.

Conditions will remain unsettled over the next couple of days as flat upper ridging centered over the southern Plains continues to interact with a weak upper low over the FL peninsula and eastern Gulf. This upper pattern coupled with a very broad region of low- level convergence, will help keep ample deep-layer moisture over the Southeast and fuel diurnal showers and thunderstorms this aftn and evening. Most of the near-term guidance continues to suggest that convective activity will initiate over the NC mountains this afternoon and then spread S/SE as the day/evening progresses. The severe risk is still looking marginally higher today as compared to the past few days, as sfc-based CAPE will likely be greater across most of our CWA this afternoon/evening. In addition, greater amounts of dCAPE are also expected across our area which should help produce stronger downdrafts. Some of the latest CAM runs continue to produce some clustering of storms near the Blue Ridge Escarpment this after- noon once the weak cap is broken, with storms then moving south and east largely on cold pools. With the weak steering flow aloft, storms will be moving slowly, thus increasing the threat for localized flash flooding today and tonight. The severe threat for Tuesday still appears lower, but it will largely depend on the amount of cloud cover across our CWA Tuesday morning and how quickly an ELY low-level flow develops. Most of the latest operational models have little in the way of a cold- air damming wedge developing east of the mtns until early Wednesday. The result is more instability across much of our fcst area on Tuesday. Although the severe threat should be lower on Tuesday, we can expect greater coverage of showers and storms Tuesday afternoon and evening with a higher risk for localized flooding. As for temperatures, highs are expected to reach 90+ degrees at most locations outside the mtns today. Values will moderate somewhat on Tuesday, but they have been trending warmer over the past few fcst cycles with most of our CWA remaining roughly 3 to 6 degrees above normal.

Key message 2: A cool-down is expected by mid-week that should keep temperatures below normal through the weekend.

On Tuesday, the northern stream becomes more blocky over the central CONUS as a mid/upper low slides underneath stout upper ridging. This results in a Rex-type blocking pattern centered to our north by mid- week. The upper low is expected to strengthen/amplify towards the end of the week and begin to move offshore over the weekend. At the sfc, cyclogenesis off the Mid-Atlantic coast is expected to bring a back- door cold front southward and thru our fcst area on Tuesday. At the same time, very broad sfc high pressure will park itself to our north over Ontario and Quebec helping to establish a cold-air damming wedge on Wednesday that will likely persist thru the end of the week. The resulting cool NELY flow and shower potential will help keep tempera- tures about 8 to 12 degrees below normal thru Friday. The wedge will likely weaken on Friday as the sfc low lifts further NE and drier air works its way into our area from the west. Nonetheless, temperatures are expected to remain below normal thru the weekend with shower chances diminishing each day from Thursday onward and increasing sunshine.

AVIATION /10Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Winds remain light and VRB through the period across all terminals. BR/FG at KAVL/KHKY dissipates after 13z, so prevailing 1/2-1SM of vsby. VFR returns after sunrise with TSRA possible at all sites this afternoon, prompting another round of PROB30s that linger past 00z. VFR cigs and calm/VRB winds return after 00z. Mountain sites KAVL/KHKY go calm overnight with IFR/LIFR BR/FG returning after 08z. MVFR cigs for KCLT toward 10z and remains in place through late morning.

Outlook: Shower and thunderstorm chances continue each afternoon through Tuesday. Pattern change after Tuesday could bring in vsby/cig restrictions. Mountain valley fog and low stratus possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...None. SC...None.