textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for the 18z aviation discussion.

KEY MESSAGES

1. Cold air damming will gradually weaken over the area, allowing temperatures to warm back above normal over the next few days. 2. Rain chances return Wednesday into Thursday as a frontal system moves through our area.

DISCUSSION

Key message 1: Cold air damming will gradually weaken over the area, allowing temperatures to warm back above normal over the next few days.

Early morning water vapor satellite imagery depicts a pronounced trough over the Four Corners region with a broad area of ascent overspreading the Great Plains. Downstream of this feature, across the Mississippi Valley, shortwave ridging continues to slide east towards the Appalachians. At the surface, high pressure that was formally situated over New York has been shunted east and offshore as the synoptic pattern remains rather progressive. This will in turn lead to eventual demise of the CAD wedge with the surface high no longer in a favorable position for CAD maintenance. Surface winds shift to out of the east today with cloud cover gradually scattering allowing for a return of sunshine. Rising heights with the approach of the shortwave ridge will also foster warming low-level temperatures with afternoon highs climbing back into the mid 60s to low 70s today. This trend persists Tuesday into Wednesday as 500mb heights rise to nearly 587dam as the pattern amplifies with the upstream trough digging across the Mississippi Valley. Temperatures will continue to be well above average for early November with afternoon highs in the upper 60s to upper 70s, some 7-10 degrees above normal.

Key message 2: Rain chances return Wednesday into Thursday as a frontal system moves through our area.

By Wednesday, a complex upper pattern will be evolving as a large scale trough ejects across the Mississippi Valley and lifts over the Appalachians. Guidance offers varying solutions as to how this feature evolves, especially in regards to the tilt of the trough and the influence of additional pieces of shortwave energy rounding the base of the trough. The GFS solution depicts a neutral to slightly negative tilt trough while the ECMWF solution maintains a positive tilt. Regardless, height falls begin to overspread the region by Wednesday afternoon with moisture return advecting low to near mid 60s dewpoints back into the area. Upslope flow will commence over the southern Blue Ridge escarpment and help to blossom at least isolated to scattered showers by early Wednesday morning. Warm advection showers will likely increase in coverage across the mountains through the day ahead of the main bout of upper forcing. The strongest height falls arrive overnight into early Thursday morning with rain chances ramping up as a pre-frontal band of precipitation pushes across the area. As of this writing, severe weather parameters are rather lackluster with meager CAPE and thermodynamic profiles. Shear profiles aren't too shabby, however, so if even a few hundred J/kg of MLCAPE can be realized a strong or marginally severe storm cannot be completely discounted, but confidence is low. Any flooding potential is also rather low as the front remains progressive along with rainfall rates being tied to convection. PWATs of 1.5-1.75" will be in the 90th percentile for early November, so isolated heavy rainfall will be possible, but dry antecedent conditions and progressive storm motion should limit any excessive rainfall threat. The front will eventually push through the area Thursday into early Friday with a return of dry weather in its wake.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: All TAF sites have returned to VFR over the past few hours, as sct to bkn lower-end VFR clouds linger over the Upstate and NC mtns. Expect the rest of the 18z TAF period to be dry and mostly VFR. The main caveat is the potential for MVFR-level stratus to spread back over the area from the south tomorrow morning. Still expect the lower clouds to remain sct at most of our sites, however I included a TEMPO for MVFR cigs at KAND and KAVL in the 10 to 14z timeframe as most of the current guidance depicts better cloud cover over those areas. Otherwise, outside the mtns, winds will remain ENE to NE thru the TAF period with speeds diminishing later tonight/ overnight. At KAVL, winds will favor a S/SSE direction thru the period, going light and VRB to calm tonight.

Outlook: Mostly dry, VFR conditions should continue through Tues. Rain and associated restrictions are expected to return Wed into Thurs as a front crosses the region. With ample cloud cover expec- ted over the next few days, mountain valley fog should be limited.

GSP WATCHES/WARNINGS/ADVISORIES

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