textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated 12Z Aviation Discussion.

KEY MESSAGES

1. Heat Advisory for parts of the Upstate/northeast GA/Metro CLT this afternoon. Hot and humid weather is expected to continue well into next week with triple digit heat index values expected outside the mountains. 2. Isolated/scattered thunderstorms are possible each afternoon/evening for the next seven days. A few could become severe with damaging wind gusts and localized flash flooding any given day.

DISCUSSION

Key message 1: Heat Advisory for parts of the Upstate/northeast GA/Metro CLT this afternoon. Hot and humid weather is expected to continue well into next week with triple digit heat index values expected outside the mountains.

The model guidance shows today to be the transition between the west-northwest flow aloft that has kept our region in the MCS track, and more of an influence from a building upper anticyclone centered over the northern Gulf Coast. As this happens, storm coverage will again be more sparse, which will allow more of a warmup today, and less mixing out of the dewpoint. The model blend dewpoints were nudged downward by incorporating some of the CAM guidance, but not enough to avoid afternoon Heat Index values creeping up above 105 across the Lakelands and parts of the CLT metro area. Confidence is higher over the Lakelands because that area got almost to 105 yesterday and today should be slightly hotter. Confidence is lower over metro CLT, but it stands to reason that urban heat island effects will be enough to raise the Heat Index above 103 across most of the metro area. ThKey message 2: Isolated/scattered thunderstorms are possible each afternoon/evening for the next seven days. A few could become severe with damaging wind gusts and localized flash flooding any given day.is also agrees well with the Advisories issued by neighboring offices.

As we go into the weekend...guidance shows the upper anticyclone covering more of the MS Valley/TN Valley and Southeast regions, and exerting more influence over the western Carolinas. Confidence is increasing that we will need a Heat Advisory over a larger area east of the mtns on Friday, unless some unexpected convective outflow manages to drop in. It is easy to imagine daily Heat Advisories all the way out thru next Thursday even as the upper anticyclone and ridge might retrograde, but especially through the weekend as the pattern supports the hot temperatures running 5-10 degrees above normal. Dog days indeed.

Key message 2: Isolated/scattered thunderstorms are possible each afternoon/evening for the next seven days. A few could become severe with damaging wind gusts and localized flash flooding any given day.

For starters, we note an area of remnant showers and a few thunderstorms moving southeastward into the southwest part of VA. On its current track, it could brush by the northwest Piedmont zones if it makes it over the mtns. The CAMs are struggling with this precip and quickly kill it off, but probably have the right idea as far as the NW Piedmont is concerned. We continue to monitor.

For today, some of the CAMs once again suggest some possible convective development along a remnant outflow from convection to the west. The environment should become reasonably unstable with the RAP showing pockets of sfc-based CAPE in the 3000-4000 J/kg range, so plenty of fuel if we can get a trigger like an outflow boundary. The precip probs will be raised slightly above the model blend because of this potential. Otherwise, the building upper anticyclone over the Southeast/TN Valley regions should shunt the MCS track more northward starting today, which will cut down on our chances for the more organized convection on Friday and through the weekend. Diurnal thunderstorms will continue with probability highest over the mtns. Any given afternoon/eve will have the potential for a few severe wind producing storms and localized flash flooding. Typical summertime stuff. As the upper anticyclone starts to weaken early next week, the MCS track could drop to the south again, but that is less certain than this past week was.

AVIATION /12Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Watching a remnant blob of showers making their way over the nrn mountains at issuance time, waiting to see if any storms will regenerate on the east side. There remains some lingering instability, so it is possible, but for now the main impact will be to KHKY. The downward trend suggests keeping them VFR in light rain, but then perhaps including an MVFR vis restriction toward daybreak with the rain-cooled air. KAVL is a tossup with the low cloud formation because of the high level convective debris moving overhead. For now I have included an MVFR restriction prevailing after 08Z, but this could easily go either way. The restrictions should end shortly after 12Z. Thereafter, prevailing VFR at all terminals. Once again, the CAMs show little in the way of convection, but with the environment we have, we prefer to include PROB30s at most terminals as a placeholder for thunderstorm activity. Later TAFs will re-evaluate. Wind light WSW away from storm outflows.

Outlook: A few showers or thunderstorms possible each afternoon with flight restrictions possible for low stratus and fog each morning.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Heat Advisory from noon today to 8 PM EDT this evening for GAZ026-028-029. NC...Heat Advisory from noon today to 8 PM EDT this evening for NCZ071-072-082. SC...Heat Advisory from noon today to 8 PM EDT this evening for SCZ009-011-014-019.