textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated the aviation discussion for the 12Z TAFs.

KEY MESSAGES

1. Above average rain chances and below normal temperatures continue through much of the week.

DISCUSSION

Key message 1: Above average rain chances and below normal temperatures continue through much of the week.

Early morning water vapor satellite imagery depicts a pronounced trough extending down the spine of the Appalachians. This feature is sandwiched between two upper ridges with one over the Desert Southwest and another just offshore over Bermuda. Heading through today, the main trough lifts northeast across New England but leaves behind a piece of energy in the base of the trough that becomes cutoff from northern stream flow. Guidance is in good agreement that an upper low will close off by this afternoon and will be stuck over the Southern Appalachians through at least mid week. By Wednesday into Thursday, an approaching longwave trough over the Great Plains will finally pick up and absorb the piece of energy, but will continue to foster at least some degree of troughing/weakness between the two pesky upper ridges.

The aforementioned synoptic pattern will favor a continued unsettled pattern across the region with the upper low supporting above normal diurnally driven rain chances each day with lower heights and sufficient cloud cover helping to keep temperatures below normal. The deep plume of moisture that extended across the area this past weekend has shifted east with a reservoir of lower PWATs (below 1.5") shifting across the Upstate and Piedmont today. This will keep the highest rain chances confined to the mountains and adjacent foothills. Coverage in diurnal showers and thunderstorms expands on Tuesday as the upper low evolves and fosters the return of east/southeast flow and moisture return. PWATs return to 1.75-2" across much of the area with at least numerous to widespread showers and storms expected. As with any summer storms, multiple days of showers and thunderstorms would support the potential for locally heavy rainfall and isolated flash flooding potential. Any flood threat should remain fairly isolated and mesoscale driven and not widespread. Additionally, an isolated strong to marginally severe storm with locally damaging winds cannot be ruled out any given day, but the overall environment will not be conducive for a more organized severe weather threat with rather lackluster thermodynamic parameters.

AVIATION /12Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: Widespread restrictions are ongoing this morning across much of the area as a deck of low stratus has built in. Ceilings range from IFR to LIFR with areas of dense fog, especially along the I-85 corridor through the Upstate (KGMU/KGSP). With time, fog will mix out and ceilings will gradually lift with a return to VFR by the afternoon. Showers and storms will be mainly focused over the mountains this afternoon (KAVL), but a few isolated showers cannot be ruled out at KHKY and KCLT. Heading into tonight, another bout of low stratus seems probable, but will likely be focused over the NC foothills and Piedmont (KHKY/KCLT) where low- level moisture return is maximized. Fog cannot be discounted across the Upstate, but confidence in where it may develop and how dense remains uncertain. And then last but not least will be mountain valley fog, which could result in restrictions at KAVL.

Outlook: Daily showers and thunderstorms, along with associated flight restrictions, linger through at least mid to late week. Patchy fog and low stratus possible in the mountain valleys each morning, and wherever heavier rainfall fell the previous evening.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Dense Fog Advisory until 10 AM EDT this morning for GAZ017-018- 026-028. NC...None. SC...Dense Fog Advisory until 10 AM EDT this morning for SCZ008-010- 104>109.