textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No significant changes at this time.

Updated for the 12z aviation discussion.

KEY MESSAGES

1. Unseasonably warm and humid conditions are expected for the remainder of the week, with shower and thunderstorm chances increasing Wednesday and remaining through Friday.

DISCUSSION

Key message 1: Unseasonably warm and humid conditions are expected for the remainder of the week, with shower and thunderstorm chances increasing Wednesday and remaining through Friday.

The upper air pattern atop the Conus will remain amplified/not especially progressive through much of the week, with even a semblance of an early week, short-lived omega block out West. The center of an upper low is forecast to lift from the Southern Plains Tuesday morning to the upper Miss Valley by Wed morning, inducing gradual height falls over the East. Associated occluding/weakening frontal zone is forecast to approach our CWA from the west on Wednesday. Persistent southerly flow ahead of this feature will result in increasing warmth and humidity over the next couple of days, with temps forecast to be (at least) 5-10 degrees above normal Tue through Wed, while surface dewpoints are forecast to increase to the 60s by Wed afternoon. Frontal zone will therefore find more than adequate moisture along with some modest instability in place as it moves into our area Wed afternoon/evening. Short term and convection- allowing guidance features fairly robust forcing, especially in the low levels as the boundary crosses the TN Valley and the Deep South Wed afternoon, but quickly weakens said forcing as the occlusion process matures over the Appalachians and points east Wed night. As a result, a strong gradient in PoPs and especially QPF is anticipated from west to east, with general 0.5-1.0" amounts currently forecast across our western third (locally higher amounts on south-facing slopes), and barely any precip forecast east of I-77.

The combination of unimpressive shear and modest instability along with the occluding nature of the front are not favorable for an organized severe storm threat, but we suppose a couple of strong- to-severe storms cannot be ruled out. Locally heavy rain is possible across western areas, especially on aforementioned south-facing slopes, with a non-zero chance of localized flash flooding Wed/Wed night.

Very little thermodynamic contrast is anticipated in the wake of the frontal zone Thursday, so conditions are forecast to remain warm and humid. While there won't be much of a source of organized lift to speak of, general cyclonic flow aloft combined with terrain effects is likely to result in some scattered convection Thu afternoon/evening. By Thu night, a weakening upper low over the Southern Plains is forecast to kick out quickly across the southeast quadrant of the country, with associated height falls introducing a cold front, and possibly another round of convection to the region late Friday. However, global models differ widely regarding the extent of any convective coverage. We advertise PoPs mostly in the 40-50% range for the time being.

Saturday is forecast to be a transition day, with temperatures remaining above normal, albeit with some degree of cool/dry air advection likely being in progress...setting the stage for a return to dry weather along with typical mid-autumn temperatures and humidity levels for early next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: A mix of VFR and MVFR this morning as bouts of low stratus push into the area from the southeast within a plume of moisture return from the Atlantic. Periodic MVFR ceilings cannot be ruled out at any given terminal through the morning hours with a return to VFR area wide by afternoon. A deeper surge of moisture surges into the region tonight ahead of an advancing cold frontal boundary. This will foster the development of a more widespread deck of low stratus with widespread MVFR anticipated along with the potential for IFR. Otherwise, winds will be generally light out of the east with variations just north and just south of east.

Outlook: Rain and associated flight restrictions should return as early as Wednesday morning, continuing through Thursday as a cold front crosses the region. VFR conditions return for the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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