textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

PoPs and QPF are trending up across the area for Saturday night thru Sunday, but confidence remains low.

The aviation discussion has been updated for the 18z TAFs.

KEY MESSAGES

1. Dry and quiet through at least Friday. Above normal temperatures return for the rest of the workweek. 2. Rain chances return to the region over the weekend, potentially lingering into early next week. Confidence on timing and details remains low at this time.

DISCUSSION

Key message 1: Dry and quiet through at least Friday. Above normal temperatures return for the rest of the workweek.

Dry sfc high pressure will persist across much of the eastern CONUS thru Friday under broad upper-level troughing. The air mass in place will warm thru the end of the workweek, with temps about 5-10 deg above normal. The warmest day of the week is expected to be Thursday, with highs about 10 deg above normal. A dry cold front slips in from the north early Friday, which may keep Friday's max temps a few deg cooler.

Key message 2: Rain chances return to the region over the weekend, potentially lingering into early next week. Confidence on timing and details remains low at this time.

The main feature to potentially impact the weather across the forecast area this weekend will be a tropical system, which will likely be a tropical depression later this aftn. The vast majority of model guidance, including ensembles, has the system become at least a Tropical Storm as it gets organized in the western Gulf, and have narrowed on the forecast track somewhere along the central Gulf Coast later this week. However, there is still a lot of spread on the speed of the storm, and hence, the timing of heaviest rainfall across the CWFA. There is still a lot of disagreement on the QPF among the deterministic models. The 12z Canadian is further west with the storm track and shows only about 0.5-1.5" of QPF, while the 12z ECMWF is coming in with widespread 2-3" with locally 4-6" along the Blue Ridge escarpment. Most of this rainfall is forecast to occur Saturday night thru Sunday, but again, timing is still low-confidence, until the tropical system gets more organized and initialized by the later model runs.

The NBM has bumped up PoPs into the categorical range for Sunday, with QPF in the middle of the model spread (mainly 1-3", locally 3-4" along the Escarpment and less than 1" along the TN border). This makes sense given the tropical moisture will be strongly forced over a hybrid cold-air damming wedge and 30-40+ kt of SELY upslope flow. If this forecast holds, this should be mainly a beneficial rain event, but locally excessive rainfall will be possible. Temps will trend cooler within the wedge, with highs mainly in the 60s to lower 70s.

The tropical system should become extra-tropical as it tracks thru the Mid-South to the Ohio Valley late Sunday thru Monday. This should result in drier air working in from the SW and tapering off rain chances. The latest NBM has trended lower for Monday's PoPs, but this remains low-confidence, given the dependence on the storm track. Dry weather with temps returning to above normal is expected by Tuesday.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

At KCLT and elsewhere: MVFR stratocu should continue to slowly lift to VFR and gradually thin out, as dry air works in from the west this aftn into early evening. Generally clear overnight, with mountain valley fog forming again like last night. Have added a tempo for LIFR conditions at KAVL, as fog may form before sunrise Wednesday. Otherwise, VFR with winds becoming light by late aftn, and likely calm or VRB overnight thru Wednesday morning. Wind is expected to toggle to light out of the S/SW at KCLT Wednesday aftn.

Outlook: VFR conditions prevail through Friday, with mountain valley fog and low stratus are possible each night. More widespread lower clouds and rain chances may return to the area as early as Saturday, but more likely later in the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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