textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Another Air Quality Alert for ground level ozone was issued for Davie County and is in effect until midnight tonight.

KEY MESSAGES

1. Hotter-than-normal conditions return today and continue into the weekend. Heat index values in the 100 to 106 degree range are expected across much of the Piedmont through Sunday. 2. Diurnal convection is expected to be mostly confined to the mountains this afternoon and evening. Shower and thunderstorm coverage will likely increase each day into the weekend as a weak cold front moves through our area.

DISCUSSION

Key message 1: Hotter-than-normal conditions return today and continue into the weekend. Heat index values in the 100 to 106 degree range are expected across much of the Piedmont through Sunday.

Broad upper ridging will be the dominant synoptic feature impac- ting the weather across the Southeast and Mid-Atlantic thru the end of the week. Above normal temperatures return to our fcst area today, with highs expected to be roughly 4 to 8 degrees above normal across the eastern third of our CWA, and roughly 3 to 5 degrees across the west. Heat indices should peak in the 100 to 104 degree range across most of our non-mtn zones, with some localized areas of 105 possible. The potential to reach Heat Advisory criteria appears a bit higher on Friday and Saturday when thickness values support slightly warmer temps, and fcst soundings suggest less dry air aloft. However, there is some potential for a broad plume of smoke from wildfires (well to our north) to spread over our area by tomorrow, which would help suppress temperatures. Having said that, confidence was not quite high enough to issue any Advisories for Fri or Sat, but one could still be issued with the next fcst package. Regardless, individuals should prepare for elevated heat risk over the next few days. Stay hydrated, take frequent breaks in air-conditioned or shaded areas, and never leave children or pets unattended in vehicles.

Falling heights/weakening of the upper ridge should result in slightly cooler temperatures by Sunday, but with lower potential for sfc dewpts to mix out during the afternoon. Nonetheless, the current fcst still has heat index values in the 100 to 103 range across the Piedmont and Upstate. This is followed by a return of more typical heat index values for the first half of next week.

Key message 2: Diurnal convection is expected to be mostly confined to the mountains this afternoon and evening. Shower and thunderstorm coverage will likely increase each day into the weekend as a weak cold front moves through our area.

With the upper ridge being the primary influence over our weather for the next few days, deep convection will be somewhat suppressed, with fcst soundings depicting generally weak capping and somewhat limited low-level moisture under deep mixing. With weaker capping expected over the mtns, isolated-to-widely scattered convection is expected over the southwest NC mtns this afternoon/evening. Slightly less capped/more unstable/more moist conditions on Friday should increase the coverage of diurnal convection across the mtns, while also increasing the potential across the remainder of our fcst area. Where convection does develop, sfc-based CAPE of roughly 2500 J/kg and robust downdraft CAPE of 1000+ J/kg will create the potential for a few strong-to-severe downbursts each day.

With heights falling across the Eastern CONUS, an increase in con- vective coverage is expected Saturday and Sunday as a weak cold front moves into our area. Slightly drier and cooler conditions early next week should result in less shower and thunderstorm coverage each day, although another cold front could enhance coverage by Wednesday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: Expect mostly dry, VFR conditions thru the 18z TAF period. A few thunderstorms have developed over the western Upstate during the past couple of hrs, with a cell just now developing near KAND. As such, I have VCTS at KAND until 00z. I expect most of this activity to remain west of the other sites, so I have no mention of convection at the other TAF sites today. We will probably see another round of mtn valley fog/low stratus overnight, but like this morning I don't think it will reach KAVL. Otherwise, winds outside the mtns will remain generally light and VRB into tomorrow morning. They will pick up marginally from the NE later tomorrow morning with speeds between 5 and 10 mph. At KAVL, winds should remain NW/N thru tomorrow morning, becoming light and VRB later in the morning.

Outlook: Coverage of afternoon/evening SHRA/TSRA will increase Friday, but chances still appear highest across the mtns. Better coverage of afternoon/evening SHRA/TSRA is expected this weekend. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

CLIMATE

RECORDS FOR 07-16

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 94 1988 69 1930 72 2020 49 1926 1980 1897 1932 KCLT 100 1899 67 1930 76 2020 58 2004 1887 1988 2001 KGSP 101 1887 65 1930 79 1937 57 1888

RECORDS FOR 07-17

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 95 1980 72 1917 77 1887 54 1939 1891 KCLT 100 1986 74 1989 80 1881 62 2004 1887 1896 1903 1886 KGSP 103 1887 76 1930 76 1934 60 1886

GSP WATCHES/WARNINGS/ADVISORIES

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