textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 06z TAFs.

KEY MESSAGES

1. Heat risk will steadily increase through the week, with heat indices likely exceeding 100 degrees across much of the Piedmont and foothills through the Independence Day Holiday Weekend. Daily thunderstorms will also be possible across the mountains. 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: Heat risk will steadily increase through the week, with heat indices likely exceeding 100 degrees across much of the Piedmont and foothills through the Independence Day Holiday Weekend. Daily thunderstorms will also be possible across the mountains.

Deep anticyclone and associated upper ridge over the MS and TN Valleys will continue to propagate eastward through the workweek and stretch out over the Mid-Atlantic and Carolinas today and Thursday, while remaining in place through late week. Anomalously warm thicknesses will support prolonged heat from through the Independence Day Holiday Weekend. Expect daily afternoon highs to be in the mid to upper 90s this afternoon and Thursday, with upper 90s to near 100 Friday into the holiday weekend. Mountain Valleys will climb into the low to mid 90s.

The one caveat into the forecast will be how high heat indices can potentially reach and whether or not multiple days of Heat Advisories will be needed. With drier air aloft and very well mixed boundary layers (top :~700mb) on the hottest days during the forecast period, dewpoints likely mix out into the low to mid 60s, with some locations getting into the upper 50s at peak heating each day. Dewpoints play a critical role into how high heat indices can reach and the current forecast suggests that values will struggle to reach Advisory criteria, but conditions will still pose an elevated heat risk, especially considering that many people will likely be outside for the upcoming holiday weekend. 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 still in play for the mountains where terrain enhancement will help to initiate isolated to widely scattered showers and thunderstorms in an otherwise suppressed atmosphere. Only very isolated convection may slip east of the mountains, but the overall expectation is for this activity to stay mostly confined to the mountains. Can't rule out a couple of storms each afternoon becoming strong to severe, which is pretty typical for early July convection.

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. 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 deep 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 /06Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR conditions will prevail at most TAF sites through the forecast period. Mountain Valley fog/low stratus will be possible again tonight, so kept the TEMPO for at least IFR vsbys/cigs at KAVL from 08Z through 12Z. VFR stratocu will come and go throughout the overnight period across the rest of the terminals. Any mountain valley fog/low stratus will dissipate shortly after sunrise. Another round of mountain showers and thunderstorms this afternoon and evening will keep the PROB30 going at KAVL for TSRA and associated restrictions during peak heating, while remaining dry with afternoon cu and some convective debris outside of the mountains. Winds will be light and variable through most of the period, but will favor a E/SE component at 4-8 kts this afternoon. Another round of mountain valley fog/low stratus will be possible tonight as well.

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