textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Heat Advisory has been issued for much of the Piedmont for Friday afternoon. Otherwise, little substantive changes.

KEY MESSAGES

1. Dangerous heat continues through the Independence Day weekend, with heat indices ranging from 100 to 110 across the Piedmont and foothills each afternoon. Mostly isolated thunderstorms are expected each afternoon/evening, mainly over the mountains. Any storm that develops will be capable of becoming briefly strong-to- severe. 2. The heat threat begins to wane early next week with a return to a more traditional mid summer pattern featuring near-normal temperatures and at least scattered diurnal convection.

DISCUSSION

Key message 1: Dangerous heat continues through the Independence Day weekend, with heat indices ranging from 100 to 110 across the Piedmont and foothills each afternoon. Mostly isolated thunderstorms are expected each afternoon/evening, mainly over the mountains. Any storm that develops will be capable of becoming briefly strong-to- severe.

An upper anticyclone will to continue to dominate the weather across the Southeast through the holiday weekend, although it will be in a weakening phase as a series of height falls impact the northeast quadrant of the country. The big story will remain the heat. If anything, Fri and Sat will be the hottest days of the week, as ambient temps are forecast to reach the century mark across much of the Piedmont...esp the I-77 corridor both days. On the other hand, forecast vertical profiles depict a little drier air mass promoting deeper mixing, which should result in surface dewpoints decreasing a bit more in the afternoon in comparison with recent days. As such, forecast maximum Heat Index values of 105 or higher are primarily confined to the extreme southern part of the forecast area, as well as the I-77 corridor. A Heat Advisory will be issued for these areas for Friday. Similar conditions are expected for Independence Day, but when the time comes...we will certainly want to entertain the idea of an "impact-based" Advisory for the holiday, even for areas where forecast H.I. is forecast to fall a couple of degrees shy of criteria. The very hot conditions continue into Sunday. 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.

Otherwise, the air mass has become strongly unstable across the southern half of the area this afternoon, with sbCAPE currently analyzed at greater than 4000 J/kg across the upper Savannah River Valley. Similar to the past couple of days...the anticyclonic flow aloft is expected to limit convective coverage to mostly isolated activity across the western third or so of the CWA...but strong buoyancy and robust downdraft CAPE (> 1100 J/kg) indicates that anything that does develop is likely to become at least strong...with a couple-ish severe storms producing damaging microbursts being a good bet. Not much change in the convective picture is expected Fri/Sat, with diurnal, mountain-centric activity expected to be isolated in coverage...while anything that does develop stands a good chance to become strong-to-briefly severe. With the ridge expected to be in a breaking-down phase by the end of the weekend, an uptick in diurnal convective activity is expected Sunday...although coverage is expected to be at most typical for early July.

Key message 2: The heat threat begins to wane early next week with a return to a more traditional mid summer pattern featuring near-normal temperatures and at least scattered diurnal convection.

The anticyclonic pattern responsible for the ongoing heat event will evolve into more of a typical southern Conus/subtropical ridge early next week, with a strengthening Bermuda high expected to support plenty of humidity across our forecast area through the week. By Monday, diurnal convective coverage is forecast to become more typical of early summer...with scattered showers and storms expected over the lower elevations, and scattered-to-numerous activity over the mountains. A couple of pulse severe storms will be possible each afternoon, with perhaps an uptick in the threat of localized flash flooding associated with slow-moving and isolated anchored cells. Forecast temps "cool" to more like 5 degrees above climo Monday, with near-normal conditions expected by mid-week.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: VFR conditions are forecast to continue at the TAF sites through this period, as a very hot air mass lingers over the region. Isolated-to-widely scattered convection is forecast to develop across the western third or so of the Terminal Forecast Area during late afternoon/early evening. In terms of the TAF sites, KAND appears to be most likely to experience a TS, and a Prob30 has been introduced there from 21-00Z. Convection could also impact the other Upstate SC terminals and KAVL, but coverage is expected to be more isolated that far N and W, so a convective mention is omitted for now. Any convection should be gone by late evening.

Low stratus and/or fog are likely to redevelop across the mountain valleys late tonight/early Fri, but is once again forecast to be confined to the valleys N and W of KAVL. Other than a period of light ENE winds this afternoon...and ESE winds late morning/early afternoon Fri, light/vrbl winds are mostly expected.

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

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. Heat Advisory from noon to 8 PM EDT Friday for GAZ029. NC...Heat Advisory until 8 PM EDT this evening for NCZ035>037-056- 057-068>072-082-502-504-506-508-510. Heat Advisory from noon to 8 PM EDT Friday for NCZ035>037-056- 057-069>072-082. SC...Heat Advisory until 8 PM EDT this evening for SCZ008>014-019- 104>109. Heat Advisory from noon to 8 PM EDT Friday for SCZ009-011>014- 019.