textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation discussion was updated for the 12z TAF issuance.

KEY MESSAGES

1. Following a protracted period of clear, dry weather, accompanied by a slow but steady warming trend lasting most of this week, the signal is getting stronger for cold-air damming to develop over the weekend. Clouds and rain are expected to return by Saturday, and a strong cooling trend may be in store by Sunday.

DISCUSSION

Key message 1: Following a protracted period of clear, dry weather, accompanied by a slow but steady warming trend lasting most of this week, the signal is getting stronger for cold-air damming to develop over the weekend. Clouds and rain are expected to return by Saturday, and a strong cooling trend may be in store by Sunday.

With a weakening coastal low now centered over the Nantucket/Cape Cod region and continuing its northeastward march, low-level northwesterly CAA has diminished somewhat across the Carolinas, leaving us in an increasingly stagnant pattern. The most recent upper-air analysis features a broad z500 ridge axis extending from the southern Great Plains, across the Ozarks, and into the Great Lakes, with weak northwesterly flow draped across the Carolinas. Water vapor imagery depicts a dry cyclonic circulation centered over the Appalachians...but think that'll pass with little fanfare tonight, other than perhaps lending an extra twinkle to the stars.

The forecast remains much the same as it has for days; upper ridging is still expected to build across the southeast over the next 24 hours or so, while at the surface broad, ill-defined high pressure will migrate off the Atlantic coast through the middle of the week, opening the Carolinas up to weak moisture return by Thursday and Friday. Some uncertainty remains in how quickly low-level upglide will begin to produce rainfall again...but long-range ensembles continue to trend more and more toward a later onset, with some 75% of the most recent LREF ensemble members now holding rain off until, at the earliest, Friday night. All three of the global deterministic models now hold rain off until early Saturday.

Having said all that, it still looks like a good case for a hybrid cold air damming setup, with incipient high pressure draped across the northeast Friday and Saturday contributing a synoptic component and the onset of rainfall providing a strong diabatic component. Still think, therefore, that a CAD wedge is likely to develop over the weekend. It should be short-lived, however, as guidance remains in excellent agreement (for this timescale) on the arrival of a strong cold front by Monday afternoon, ushering in a cool cP air mass by the end of forecast period. Accordingly, the latest forecast features cloudy skies and a strong cooling trend over the weekend...with highs in the 70s by Sunday and Monday...and lows approaching their coolest so far this fall to start out next week.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Expect dry, VFR conditions and mostly clear skies to continue thru the 12z TAF period. Over the past few hrs, mountain valley fog/low stratus has developed again in the usual locations, but it's not expected to impact KAVL. Winds should be light thru the TAF period (generally 5 kts or less). They will continue to favor a N to NE direction, but will be light and VRB to calm at times thru the day/evening.

Outlook: Dry, VFR conditions should persist thru Thursday. Moisture will begin to increase across the area on Friday, with a chance of showers by Friday afternoon over the mountains and more widespread showers across the area on Saturday. Mountain valley fog/low stratus remains possible each morning.

GSP WATCHES/WARNINGS/ADVISORIES

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