textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12z TAFs.

KEY MESSAGES

1. Dangerous heat continues to build through the week and into the Independence Day Holiday Weekend, with heat indices likely reaching or exceeding 105 degrees across much of the Piedmont and foothills. Isolated strong to severe storms possible today. Daily thunderstorms will also be possible across the mountains through the weekend. 2. The heat threat begins to wane late weekend and into early next week with a return to a more traditional mid summer pattern featuring seasonable temperatures and daily storm chances.

DISCUSSION

Key message 1: Dangerous heat continues to build through the week and into the Independence Day Holiday Weekend, with heat indices likely reaching or exceeding 105 degrees across much of the Piedmont and foothills. Isolated strong to severe storms possible today. Daily thunderstorms will also be possible across the mountains through the weekend.

An anticyclone and associated upper ridge has set up shop over the eastern CONUS with anomalously warm thicknesses. The ridge will gradually propagate eastward through the holiday weekend. As a result, expect very hot temperatures with afternoon highs in the upper 90s to low 100s each day through at least Saturday across the foothills and Piedmont. A few locations may approach 102-104 degrees for afternoon highs. Mountains valleys will be hot as well with afternoon highs in the low to mid 90s, with low to mid 80s at the highest elevations.

The continued forecast uncertainty is how much dewpoints mix out each day during peak heating and how that impacts heat indices. Vertical profiles continue to support very well mixed boundary layers that extend to at least 750-700mb, possibly higher Friday and Saturday. In this case, dewpoints will mix out into the upper 50s to low 60s Friday and Saturday, which could keep heat indices below advisory criteria despite very hot air temperatures. Forecast soundings for this afternoon indicate lingering moisture in the boundary layer and don't mix out as much as it is anticipated for Friday and Saturday. This will be enough to promote a Heat Advisory for all of the foothills and Piedmont of the western Carolinas and northeast Georgia with dewpoints forecast to remain mostly in the upper 60s and low 70s during peak heating. The Heat Advisory will run from noon to 8 PM EDT this evening. 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.

Daily afternoon convection is expected for the mountains today through at least Saturday where terrain enhancement will help to initiate isolated to widely scattered showers and thunderstorms. CAMs have been more aggressive with today's convection and produces more coverage outside of the mountains, mainly over the North Carolina foothills, Upstate South Carolina, and northeast Georgia as convection potentially becomes outflow driven. Despite the compressed atmosphere with very warm air aloft, deep instability (3000-4000+ J/kg of SBCAPE), steep lapse rates, and large DCAPE will support isolated instances of strong to severe storms capable of producing locally damaging winds and large hail in the aforementioned areas. Convection is expected to remain mostly confined to the mountains Friday and Saturday and with the typical mid summer environment, can't rule out a couple storms becoming strong to severe.

Key message 2: The heat threat begins to wane late weekend and into early next week with a return to a more traditional mid summer pattern featuring seasonable temperatures and daily storm chances.

The upper ridge that will be responsible for the prolonged heat this week will gradually break down and shift over the western Atlantic by late weekend into early next week. In response, afternoon highs will drop into the low to mid 90s, which is at or slightly above normal for early July. As a result, triple digit heat indices should be held in check outside of the southern and eastern zones. Temperatures remain hot for Sunday and could support another day of dangerous heat, but will be dependent on how much moisture returns to the boundary layer and the extent of afternoon/evening convection and debris. Deepening upper ridge over the Rockies and High Plains will send weak northwest flow aloft downstream into the area with multiple rounds of weak embedded shortwaves, while increasing moisture advection from the Gulf and Atlantic sets the stage for more scattered to numerous diurnal showers and thunderstorms each day. A few strong to severe storms can't be ruled out each day with locally damaging winds and small hail as the primary threats.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions will prevail through the period. The mountain valley fog/low stratus fell short of reaching KAVL, so took out the TEMPO for the 12Z update. Any mountain valley fog/low stratus will quickly dissipate after sunrise. Afternoon cu is expected to develop again at all terminals. Scattered showers and thunderstorms are possible in the afternoon with more of the activity possibly pushing outside of the mountains. As a result, placed a PROB30 for TSRA and associated restrictions for the Upstate terminals and KAVL during peak heating. Any convective debris should scatter out later this evening. Another round of mountain valley fog/low stratus is possible tonight.

Outlook: Diurnal showers and thunderstorms are expected to continue through the holiday weekend, mainly across the mountains. 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 GAZ018-026-028-029. NC...Heat Advisory from noon today to 8 PM EDT this evening for NCZ035>037-056-057-068>072-082-502-504-506-508-510. SC...Heat Advisory from noon today to 8 PM EDT this evening for SCZ008>014-019-104>109.