textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

A Heat Advisory has been issued for all areas outside the mountains for Saturday afternoon. Otherwise, little substantive changes.

KEY MESSAGES

1. Dangerous heat continues east of the mountains through the Independence Day weekend before the heat gradually wanes next week. 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. 2. Isolated to widely scattered diurnal showers and storms are expected mainly over the mountains through the Independence Day weekend, with chances increasing for all areas next week. Per usual, a few storms could become strong to severe during peak heating hours, with the main hazard being damaging wind gusts. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

DISCUSSION

Key message 1: Dangerous heat continues east of the mountains through the Independence Day weekend before the heat gradually wanes next week. 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.

The center of the upper anticyclone bringing about the very hot conditions will migrate from the Carolina/Virginia Piedmont this afternoon, to Cape Hatteras by the end of Saturday...weakening as it does so, as the westerlies become increasingly active with areas of height falls across the northern Conus. The heat will remain oppressive through the weekend, before steadily waning early in the work week, with near-normal temperatures expected by the mid-week. While Saturday's ambient temperatures are expected to be just as...if not slightly warmer than today, vertical profiles are also forecast to be a little drier and promote deeper mixing, with surface dewpoints forecast to lower to the mid...if not lower 60s during the afternoon. Having said that, max forecast Heat Indices are still in the 101-106 range across much of the Piedmont and foothills. In light of the plethora of festivals and other outdoor activities...and tomorrow being the 5th consecutive day of very hot weather, an "impact-based" Heat Advisory will be issued for all non-mountain forecast zones.

Slightly "cooler" temperatures are forecast Sunday, but the atmosphere will also begin moistening up. As such Sunday Heat Indices will only be marginally...if at all...different than Saturday...and another Heat Advisory is likely to be needed for a good portion of the CWA. Although temperatures will continue to slowly decline early in the work week, afternoon dewpoints will also be increasing as an intensifying Bermuda High will support moisture transport into the Southeast. Therefore, the triple digit Heat Indices may abate for much of the forecast area, but upper 90s are forecast to be common outside the mountains through much of the week.

Key message 2: Isolated to widely scattered diurnal showers and storms are expected mainly over the mountains through the Independence Day weekend, with chances increasing for all areas next week. Per usual, a few storms could become strong to severe during peak heating hours, with the main hazard being damaging wind gusts. Make sure you have multiple ways to receive warnings, especially if you have outdoor plans.

Deep easterly flow circulating around the south side of an anticyclone has shunted slightly drier air into the CWA today compared with yesterday. As such, conditions are not quite as unstable this afternoon, and the bulk of regional convective activity is concentrated across central and north Georgia. Having said that, conditions are still quite unstable across our CWA (sbCAPE mostly 3000-4000 J/kg) and the cu field is becoming steadily-but-surely more agitated. Isolated-to-widely scattered deep convection should begin developing over the mountains and foothills by mid-afternoon, continuing through the afternoon before dissipating this evening. Weak low level shear and downdraft CAPE > 1000 J/kg indicate microbursts from single cell pulse storms will be a possibility with deeper updrafts. For now, Saturday's convective picture looks very similar to today, with isolated/widely scattered, mostly mountain activity and a handful of pulse severe storms expected.

With the anticyclone expected to weaken early next week...and the upper pattern evolving into one characterized by more of a typical/broad subtropical ridge over the Southeast. Bermuda High will assert itself across the western Atlantic, supporting elevated moisture across the region throughout the week. By Monday...PoPs for diurnal convection increase to values more typical (if not a little higher) for the time of year (mostly likely across the mtns; solid chances elsewhere.) More or less typical early summer convective weather is expected for the remainder of the week.

AVIATION /20Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR is forecast to continue at the TAF sites through this forecast cycle. Mostly isolated convection is expected to develop across the mountains and foothills by mid-afternoon. Based upon the latest data, KHKY stands the best chance of seeing a TS, and we opted to introduce a Prob30 for TSRA there from 20-23Z. Again...convection could impact the other sites...especially KGMU/KGSP and KAVL, but chances are < 30%. Mountain valley fog/low stratus will again develop overnight into early Sat, but should again primarily impact areas W through N of KAVL. General light SE winds this afternoon will become light/vrbl or calm this evening.

Outlook: Diurnal showers and thunderstorms are expected to continue, mainly across the mountains, through the holiday weekend. Better chances for diurnal convection are forecast through the new work week. Low stratus and/or fog will be possible each morning, mainly in the mountain valleys.

CLIMATE

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 Saturday 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. Heat Advisory from noon to 8 PM EDT Saturday 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. Heat Advisory from noon to 8 PM EDT Saturday for SCZ008>014- 019-104>109.