textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Another round of showers and thunderstorms west of I-26 possible this afternoon and evening, with one or two storms potentially becoming strong to severe. 2. Heat risk will steadily increase through this week, with heat indices likely exceeding 100 degrees across much of the Piedmont and foothills, especially by mid to late week.

DISCUSSION

Key message 1: Another round of showers and thunderstorms west of I-26 possible this afternoon and evening, with one or two storms potentially becoming strong to severe.

Most of the shower and thunderstorm activity overnight over the southwest mountains has dissipated. Any lingering mountain valley fog and low stratus will scatter out by mid morning.

Continued northwest flow aloft thanks to a deepening upper-level ridge to the west and the presence of a weak frontal boundary draped along the I-26 corridor, isolated convective initiation is possible during peak heating west of I-26. CAMs vary as far as coverage and intensity, but deep moisture (PWAT >1.50"), sufficient SBCAPE (2000-3000 J/kg), and 20-30 kts of 0-6 km bulk shear on the west side of the boundary suggests that the environment could be enough to support loosely organized convection capable of a strong to severe thunderstorm or two, producing damaging winds. Guidance continues to pinpoint the western Upstate as having the highest probability of a severe storm, but can't be ruled out elsewhere west of I-26. Afternoon highs are forecast to run a category or so above normal, with the southern tier of the CWFA potentially exceeding 100 degree heat indices before any afternoon convection arrives.

Key message 2: Heat risk will steadily increase through this week, with heat indices likely exceeding 100 degrees across much of the Piedmont and foothills, especially by mid to late week.

An upper-level ridge will strengthen across the eastern CONUS this week, bringing a steady warming trend and suppressing convective coverage. High temperatures are expected to climb into the lower to mid 90s east of the mountains today and Tuesday, with values running 5-10 degrees above normal by mid to late week and the Independence Day Holiday Weekend.

Heat index values may approach or exceed 100 degrees starting today through Wednesday, with possible Heat Advisory criteria by Thursday into the holiday weekend. Confidence in exact heat values remain somewhat limited due to uncertainty in afternoon dewpoints potentially mixing out with notable subsidence in the vertical column as heat index values are highly sensitive to dewpoint values. With the ridge in place, convective coverage will be reduced as most activity becomes isolated to scattered and stays mostly confined to mountains during each afternoon and evening, with very isolated instances of convection east of the mountains. Current guidance suggests the synoptic pattern causing the potential prolonged heat could persist through the holiday weekend with little indication of significant relief. While Heat Index for the next couple of days is forecast to be at least several degrees below Advisory criteria, values of around or slightly below 105 are expected to creep into Elbert County, Georgia this afternoon. In collaboration with NWS FFC, Elbert Co will be included in a Heat Advisory. Heat Advisories are likely to continue through the week, while gradually expanding in coverage.

Those with outdoor plans, including holiday and recreation, should prepare for several days of elevated heat risk. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

AVIATION /12Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Mostly VFR conditions expected through the forecast period outside of potential mountain valley fog/low stratus through daybreak. Updated KAVL to include an MVFR cig TEMPO mention through 13Z, while removing any mention of fog/low stratus elsewhere as confidence is too low for a TAF mention. Winds are generally light and variable through daybreak and pick up out of the northeast during the daytime period, while KAVL maintains a north to northwesterly component through the period. Guidance continues to develop showers and thunderstorms over the western half of the area, with the best chance of any shower or thunderstorm mention with associated restrictions remaining over KAND and KAVL. Placed a PROB30 for TSRA at KAND and a VCSH mention at KAVL as a result. Lingering convective debris and afternoon cu will keep low VFR cigs in place during the afternoon, but should scatter by this evening into the overnight hours tonight. Another round of mountain valley fog/low stratus is possible overnight tonight.

Outlook: Diurnal showers and thunderstorms are expected mainly across the mountains through the workweek. Mountain valley fog/low stratus will be possible each morning.

CLIMATE

RECORDS FOR 07-02

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 93 1970 65 1943 70 2018 44 1988 1954 1931 KCLT 101 1931 64 1943 76 1991 56 2008 1970 1931 KGSP 101 1954 66 1943 77 1931 53 1899

RECORDS FOR 07-03

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 93 1970 65 1988 70 2018 50 2008 1897 1931 1937 1932 KCLT 99 1931 70 1988 76 1925 56 2010 KGSP 99 2016 70 1988 77 1925 56 1984 1970 1953

RECORDS FOR 07-04

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 97 1948 68 1976 70 2016 51 1986 KCLT 99 1993 70 1968 76 1993 55 1933 1955 KGSP 100 1993 70 1988 75 2018 58 2021 1996 1933

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from noon today to 8 PM EDT this evening for GAZ029. NC...None. SC...None.