textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Heat Advisory will be allowed to expire on time. Updated the aviation discussion for the 00Z TAFs.

KEY MESSAGES

1. A very hot Independence Day weekend will steadily give way to more typical early summer heat during the new week. Diurnal convection is expected to remain largely confined to the mountains today, but a transition to a more active diurnal convective cycle is expected beginning Sunday. Those with outdoor plans for the holiday weekend should prepare for elevated heat risk. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

DISCUSSION

Key message 1: A very hot Independence Day weekend will steadily give way to more typical early summer heat during the new week. Diurnal convection is expected to remain largely confined to the mountains today, but a transition to a more active diurnal convective cycle is expected beginning Sunday. Those with outdoor plans for the holiday weekend should prepare for elevated heat risk. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

Heat index values are dropping as temps cool this evening. Will allow the Heat Advisory to expire at 8 PM.

Convection is on the wane with loss of heating. Isolated convection will linger into early evening before completely dissipating. Can't rule out a strong storm before they dissipate, but the chance is diminishing as well.

A transition to more of a cyclonic upper flow pattern is expected across the southern/central Appalachians and vicinity on Sunday, with deep, albeit weak SW flow resulting in an increase in deep layer moisture. Temperatures will remain above normal...and a few spots across the lowest elevations could again reach the century mark...but temps overall should be a little cooler than today. With the increasing moisture, surface dewpoints will have less of a tendency to mix out during the afternoon. Instability should again be quite robust, although moist adiabatic mid-level lapse rates should yield sbCAPE more typical of early summer. Overall, conditions will be much more favorable for deep convection Sunday afternoon/evening, with likely PoPs warranted across the mountains, and generally 30-50% chances elsewhere. Typical isolated strong-to-severe pulse storms along with areas of locally heavy/possibly excessive rainfall can be expected. We still can't rule out portions of the eastern and southern fringe of the CWA at least flirting with Heat Advisory criteria before the convection develops in earnest, but confidence in this is modest at best, and after collaboration with neighboring NWS offices, it was decided to withhold heat products for Sunday.

The westerlies are forecast to remain quite active to our north through the new week, with multiple rounds of height falls forecast. This will steadily lower heights across our region as the week progresses. A weak frontal system may cross the region Tuesday in association with one of these height fall surges...possibly enhancing diurnal convective chances and a slight uptick in the severe storm potential. Either way, thermal profiles and the synoptic pattern should support solid scattered-to-numerous coverage of diurnal showers and storms Mon and Tue. Somewhat drier air may advect into the region by Wed in the wake of aforementioned front, but this is unlikely to be enough to preclude diurnal convection during the latter half of the week. Nevertheless, PoPs for Wed-Fri do decrease a bit from their Mon/Tue peak. Temperatures otherwise steadily decrease through the first half of the week...to around 5 degrees above climo for Monday...to just slightly above normal for Wed/Thu.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: VFR conditions are forecast to prevail at the TAF sites through this forecast period. Convection is on the wane and should end by early evening. Low stratus and/or fog will redevelop in the mountain valleys overnight into early Sunday, but restrictions are again very likely to remain confined to the valleys W through N of KAVL. Moisture ramps up during the daylight hours Sunday, and this will lead to much improved chances for diurnal convection...with Prob30s entering the picture at KAVL by 16Z, KHKY by 18Z, KGSP/KGMU by 19Z, and at KCLT/KAND by 20Z. Winds will be mostly light SSW through the period except for KAVL where light NW wind will be seen.

Outlook: Mainly afternoon/evening shower and thunderstorm chances will continue through the week. Low stratus and/or fog will be possible each morning, especially in the mountain valleys, but also in locations that see appreciable rainfall the previous afternoon/evening.

CLIMATE

RECORDS FOR 07-05

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 96 1948 71 1976 70 2024 46 1967 2018 1933 KCLT 101 2024 66 1892 78 2024 57 1967 KGSP 101 2024 70 1976 78 2016 58 1967 1933 1892

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory until 8 PM EDT this evening for GAZ018-026-028- 029. NC...Heat Advisory until 8 PM EDT this evening for NCZ035>037-056- 057-068>072-082-502-504-506-508-510. SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019- 104>109.