textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Aviation discussion updated for the 00Z TAF cycle.

KEY MESSAGES

1. Quiet weather with above-normal temperatures will continue through Friday. 2. Widespread rain is expected to return to the region over the weekend, with locally heavy rainfall possible.

DISCUSSION

Key message 1: Quiet weather with above-normal temperatures will continue through Friday.

Dry weather is expected to continue thru Friday, thanks to sfc high pressure persisting across the Southeast. Temps will warm to about 10 degrees above normal Thursday, then get knocked down a few degrees on Friday due to a weak front slipping in from the north. An upper ridge will build over the western Atlantic, while a large longwave trough digs across the western US. This flow is expected to steer T.C. Isaias northward toward the central Gulf Coast. Thickening high clouds may stream over the area ahead of the storm and combine with cooler air advecting in from the NE to knock temps down several degrees on Friday, but still slightly above normal. Deeper moisture and rain chances from Isaias are not expected to affect the CWFA thru Friday evening.

Key message 2: Widespread rain is expected to return to the region over the weekend, with locally heavy rainfall possible.

Tropical Storm Isaias continues to become gradually more organized over the southwestern Gulf, and is expected to eventually turn toward the north, strengthen into a hurricane and make landfall somewhere along the central Gulf Coast late Friday (refer to the NHC for latest position and forecast). Guidance is coming into better agreement on the track and trending a little faster on the storm's movement. This trend is resulting in an earlier onset of rainfall from south to north Friday night, with the heaviest rain/highest PoPs now more squarely on Saturday. With that said, some model guidance still is slower and the NBM has categorical Pops linger into Sunday. As Isaias tracks north into the Mid-South, a hybrid cold-air damming wedge will set up, with a 30-40-kt SELY LLJ on the eastern side of Isaias's circulation over the wedge. As for storm total rainfall amounts, not a lot of change from previous forecast, with 1-3" across most of the forecast area, except less than 1" along the TN border and locally 3-4" along the Blue Ridge Escarpment. There is some hint that heavier rain will set up along the coastal front, where better instability and frontogenesis will be. This could interrupt moisture transport, and help keep rainfall totals over the CAD wedge and the SELY upslope areas in check.

With CAD in place, instability will be mainly elevated thru most of the event. Cannot rule out a cold-front-like line of convection forming, as Isaias quickly transitions to an extratropical cyclone and a dry slot punches in from the west on Sunday. The 00z ECMWF shows the most overlap of bulk shear, sbCAPE, and moisture to support convection and a non-zero severe threat. But overall tropical tornado threat should stay to our south and west.

With the faster storm track, PoPs continue to decrease for Sunday night thru Monday, with dry weather likely returning by Monday morning (except for a few showers possible along the TN border). Dry weather is expected to continue thru the middle of next week, with temps returning to slightly above normal.

AVIATION /00Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: VFR conditions prevail across all terminals through the TAF period. SKC overnight with SCT250 possible Thursday afternoon. Winds remain VRB through the period, with winds becoming NE at KCLT toward Thursday night. Yet another round of BR and LIFR cigs at KAVL, so a TEMPO from 09z-13z. No other vsby/cig issues.

Outlook: VFR conditions prevail through the end of the week. Mountain valley fog and low stratus are possible each night. Restrictions return for the weekend and improve by Monday.

GSP WATCHES/WARNINGS/ADVISORIES

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