textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 00z TAF issuance.

KEY MESSAGES

1. The severe threat remains low through Monday before increasing ahead of a cold front Tuesday afternoon and evening, possibly lingering into Wednesday. A warming trend is expected through early next week, with slightly cooler highs returning behind the front mid to late week.

DISCUSSION

Key message 1: The severe threat remains low through Monday before increasing ahead of a cold front Tuesday afternoon and evening, possibly lingering into Wednesday. A warming trend is expected through early next week, with slightly cooler highs returning behind the front mid to late week.

A large upper anticyclone meanders over the western and central United States while upper troughing remains the dominate feature over the eastern United states through next weekend. This will essentially keep the Southeast in a "Ring of Fire" pattern through much of the forecast period as storm complexes round the eastern periphery of the upper anticyclone. With the coverage of showers and thunderstorms expected to be less Sunday into Monday, the severe threat should remain low. A few strong,sub-severe storms are possible each day during peak heating and an isolated severe storm or two cannot entirely ruled out. The severe threat ramps up Tuesday afternoon and evening ahead of a cold front. Deep layer shear Tuesday afternoon and evening will be impressive for this time of year, ranging from 30-35+ kts. This amount of shear combined with surface instability ranging from roughly 1,800-2,500 J/kg Tuesday afternoon/evening (per the 06Z global models) will bring a higher concern for severe thunderstorms. The Day 4 Severe Weather Outlook showing a Slight Risk in place across much of western North Carolina (outside the southern NC mountains) and a sliver of the northern SC Upstate appears warranted. Although our forecast area is not highlighted in a severe risk for Day 5 (Wednesday), depending on the exact track and evolution of the MCS ahead of the front, the severe threat could linger into at least early Wednesday. However, confidence is low at this time. Damaging wind gusts would be the main potential hazard with any severe storms that develop through Wednesday. Brief drying may develop on Thursday behind the front before shower and thunderstorm chances return starting Friday as the front stalls over the Southeast.

A warming trend is expected through Tuesday ahead of the front with slightly cooler highs returning behind the front mid to late week. Tuesday still looks to be the hottest day of the week with highs ranging from the low to mid 90s and heat indices climbing into the upper 90s to lower 100s east of the mountains. However, confidence on highs on Tuesday is low as the MCS could act to limit afternoon temperatures but this will be highly dependent on the exact timing of the MCS.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Although cloud cover has sct some this aftn/ evening, we still have a few sites reporting MVFR cigs (including KAVL). In addition, shower activity has picked up a bit over the past few hrs. With some lingering instability over the Upstate, I included VCTS for KGSP, KGMU, and KAND for the next few hrs and VCSH for KAVL. SHRA chances return overnight and into Sunday morning, with the best coverage expected over the NC mtns. Confidence wrt timing of SHRA remains low as high-res models are not in very good agreement. As such, I have VCSH at all our TAF sites (with a TEMPO for SHRA at KAVL) beginning around 08z. Otherwise, conditions will gradually deteriorate again overnight into daybreak Sunday with mainly MVFR to IFR cigs/visby expected with TEMPOs for LIFR cigs at most sites. Restrictions (especially cigs) will likely be slow to improve Sunday morning, with some sites not seeing VFR conditions until roughly noon. Sct TSRA are possible again Sunday aftn/evening across the area. This was handled with PROB30s for TSRA at most sites beginning around 18z tomorrow. Otherwise, winds will be light and VRB to calm thru the period, although winds at KAVL could favor a NW/N direction beginning late Sunday morning.

Outlook: Drier conditions expected late Sunday into Monday, with only isolated TSRA expected Monday afternoon/evening. Strong to severe thunderstorms, as well as, breezy SW winds are possible Tuesday afternoon/evening ahead of a cold front. The severe storm threat could linger into early Wednesday, but confidence is low at this time. Low stratus and/or fog will be possible each morning, mainly in the mtn valleys.

GSP WATCHES/WARNINGS/ADVISORIES

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