textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The aviation forecast was updated to reflect the impending 12z TAF issuance.

KEY MESSAGES

1. A round of much-needed rainfall will provided some relief from ongoing drought conditions Saturday, as a cold front crosses the area from the west. 2. A series of frontal systems have the potential to bring rain chances next week. However, confidence is low regarding the daily forecast as timing differences continue in the model guidance.

DISCUSSION

Key message 1: A round of much-needed rainfall will provided some relief from ongoing drought conditions Saturday, as a cold front crosses the area from the west.

Widespread cirrus now in place across most of the forecast area, and continuing to thicken upstream. Aloft, a broad, low-amplitude shortwave is now centered over western Tennessee. Patchy showers continue across eastern Tennessee, with a few approaching the NC-TN state line. Today's weather will be driven by the advancement of this system across the Carolinas.

Generally think cloud cover will steadily increasing through the overnight and into Saturday morning, as the front marches eastward. SW winds should steadily strengthen ahead of it, with gusts up to 20mph expected by early afternoon. Convection, mostly showers at first, will creep out of Tennessee into the NC mountains by noon, then pivot across the CWA through the afternoon. The setup doesn't look great for either severe or heavy rainfall: a lack of robust synoptic forcing will prevent lapse rates from steepening ahead of the front, and dewpoints within the prefrontal trough will only climb into the upper 50s. So, forecast profiles from the hi-res guidance only support 400-800 J/kg sbCAPE across most of the area...and a lack of stronger flow aloft results in negligible shear in all but the most aggressive REFS solutions (and the usually-overdone NAMnest). So, there's neither support for the organization required for a better severe threat nor the strong, deep, and warm updrafts needed for heavy rain. All told, some non-severe embedded thunder is expected, with the 00z HREF's PMM fields supporting 0.25"-0.5" of rain, with isolated areas receiving >0.5". Drops in the bucket that is our current drought status...but every one of those drops will help!

Rainfall and lingering thunder should push east by late evening and into early Saturday night. Widespread cloud cover is expected to remain in place through early Sunday morning, when moisture will finally be scoured out by weak postfrontal CAA...on the leading edge of another dry air mass.

Key message 2: A series of frontal systems have the potential to bring rain chances next week. However, confidence is low regarding the daily forecast as timing differences continue in the model guidance.

Ridging surface and aloft on Monday will bring a dry conditions with near normal temperatures. A series of shortwaves then cross the area through the end of the of period. The guidance is in general agreement that a cold front moves near the area Tuesday then stalls. A low pressure system will move along the front pushing it south of the area by Wednesday night. Precip chances increase Tuesday, favoring the mountains, with likely to categorical PoP spreading over the area Wednesday. There will be enough instability and forcing for scattered thunderstorms, but little chance of severe storms. Rainfall amounts are forecast to remain in the beneficial range with little chance of flooding. Temperatures will be a little below normal Tuesday then near normal Wednesday.

The differences really develop Thursday and Friday. The front may stall close enough to the region to keep a moist, easterly flow over the area, or it may move far enough south for a dry air mass to move in. A wave develops along the front to the west and may move fast enough to bring precip chances by the end of the day, or it could move more slowly keeping most rain chances Friday night or Saturday. The model blend has low end precip chances on Thursday and moderate chances Friday. Again, this is highly uncertain at this time. The blend also has temps near normal Thursday and below normal for Friday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Finally a little action in the upcoming TAF period as a cold front crosses the area today. Already seeing extensive prefrontal cirrus expanding across the terminal forecast area from the west, and expect that cirrus to continue thickening through mid-morning. Then, as the front draws nearer...expect a FEW/SCT cu field to develop by late morning...albeit with unseasonably high bases at FL060-080. By late morning scattered SHRA should arrive in the NC mountains, and pivot eastward through the afternoon as the front crosses the western Carolinas. Expect some embedded TSRA...but couldn't justify more than PROB30s for mid/late afternoon, when instability will be maximized. Expect precipitation to end by late evening, but in its wake several guidance sources depict lingering MVFR cloud bases (and perhaps patchy fog) across parts of the Upstate and Piedmont.

Outlook: Generally dry and VFR conditions are expected to return Sunday and Monday. Another cold front will cross the area on Tuesday, bringing rain chances and possible flight restrictions.

GSP WATCHES/WARNINGS/ADVISORIES

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