textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

SPC expanded the marginal risk for severe weather across nearly the entire GSP forecast area for this afternoon and early evening.

KEY MESSAGES

1. Hot and humid conditions will return each day east of the mountains this week. Those with outdoor plans should stay hydrated and take frequent breaks in air-conditioned or shaded areas. Do not leave children or pets in unattended vehicles. Car interiors will reach lethal temperatures in a matter of minutes. 2. Coverage of diurnal showers and thunderstorms increases for all areas early this week before coverage becomes more confined to the mountains mid to late 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: Hot and humid conditions will return each day east of the mountains this week. Those with outdoor plans should stay hydrated and take frequent breaks in air-conditioned or shaded areas. Do not leave children or pets in unattended vehicles. Car interiors will reach lethal temperatures in a matter of minutes.

Although portions of the Charlotte Metro and the Upper Savannah River Valley could flirt with Heat Advisory criteria this afternoon with the return of higher dewpoints, coverage of convection should help limit heat indices. So, even if these areas manage to reach advisory criteria (which starts at 105) it should remain brief. Thus, opted not to issue a Heat Advisory for today in collaboration with neighboring WFOs. The same thinking also applies to Monday regarding heat indices.

With the worst of the oppressive airmass finally behind us, we will go into more of a typical summertime pattern as the Bermuda High sets up over the western Atlantic. This will help keep low-level flow mostly SW'ly through the week, which will allow dewpoints to range from the upper 60s to lower 70s east of the mountains. With highs east of the mountains expected to range from the lower to mid 90s each afternoon (starting Monday) and lows each night only falling into the lower to mid 70s, expect warm and muggy nights and hot and humid days to continue this week.

Key message 2: Coverage of diurnal showers and thunderstorms increases for all areas early this week before coverage becomes more confined to the mountains mid to late 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.

The aforementioned Bermuda High will work with fairly persistent upper troughing over the Eastern CONUS to bring better coverage of mostly diurnal convection through at least early this week. Slightly drier conditions may return behind a cold front Wednesday into Friday per the global models and per the latest NBM, which mostly show convection being confined to the mountains during this timeframe. The NBM and global models then show the potential for all areas to see better chances for convection next weekend but confidence is low at this time with this being towards the end of the forecast period.

Regarding the severe weather potential, SPC expanded the Marginal Risk for this afternoon and early evening across nearly the entire GSP forecast area. This seems reasonable as both global models and 00Z CAMs depict around 1,500-2,500 J/kg of SBCAPE developing during peaking heating hours. With only 10-15 kts of deep layer shear expected (as we often see this time of year) damaging winds from microbursts will be the main hazard with any severe storms that develop. We should have a fairly similar environment in place for Monday. However, confidence is fairly low regarding the coverage of storms today as the majority of the 00Z CAMs show isolated to scattered activity at best while the 00Z HRRR shows numerous showers and thunderstorms developing during peak heating. Confidence on coverage on Monday is higher as 00Z CAMs appear to be in better agreement. Chances for severe storms will continue into Tuesday as 1,500-2,500 J/kg of SBCAPE will be in place during peak heating again, per the global models. The one change is that deep layer shear will increase slightly ahead of the front on Tuesday, ranging from 20-30 kts. Thus, a more organized severe threat could materialize Tuesday afternoon/evening ahead of the front. Although lower wind shear should return behind the front the rest of the week, we should see decent destabilization each afternoon/evening so the isolated severe weather potential will stick around.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Dry and VFR through the 06Z TAF period outside of patchy morning fog/low stratus and TSRA this afternoon and evening. Maintained PROB30s for TSRA and associated restrictions across all terminals rather than upgrading to TEMPOs as 00Z high-res model guidance sources are not in agreement regarding the overall coverage of convection. Hopefully the 06Z high-res guidance will paint a more consistent picture. Have some patchy fog impacting the Little TN valley as well as KHKY this morning. Have a TEMPO at KHKY for IFR vsbys the next 4 hours. Confidence is low on whether fog will stick around through daybreak at KHKY. However, confidence is high that mountain valley fog/stratus will expand and thicken through daybreak, especially across the Little TN Valley. Fog and stratus are not expected to make it to KAVL. Wind direction should stay mostly calm to light and VRB at KAVL through the period. Winds east of the mountains will remain calm to light and VRB through the morning hours before picking up out of the S/SW by early afternoon. Winds east of the mountains appear to go VRB late afternoon/early evening before going calm again overnight. However, KCLT should see S/SW winds return by early evening.

Outlook: Mainly afternoon/evening shower and thunderstorm chances will continue through early this week. Afternoon/evening shower and thunderstorm chances will become more confined to the mountains mid to late week. Low stratus and/or fog will be possible each morning in the mountain valleys and 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...None. NC...None. SC...None.