textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

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

KEY MESSAGES

1. Mild temperatures and near-critical relative humidity continue on Friday and Saturday, mainly east of the mountains. 2. Widespread rain is expected Saturday night through Sunday night. This will mainly be a beneficial rainfall with little to no hydro impacts expected. 3. Temperatures warm early to middle next week with a return of dry weather.

DISCUSSION

Key message 1: Mild temperatures and near-critical relative humidity continue on Friday and Saturday, mainly east of the mountains.

A 1025mb surface high presently located over the upper Ohio Valley will migrate southeastward into the Carolinas through Friday evening, bringing with it increasingly lax winds alongside very dry profiles. Model soundings depict the driest air aloft over the NC Piedmont and eastern SC Upstate, supportive of RH as low as 20-24% during peak heating. For now, most guidance depicts winds remaining light - which jives with the high's position directly over us on Friday - and so no Fire Danger Statement is needed at this time, though low-end fire weather issues remain a concern.

Low relative humidity should develop again on Saturday across most of the low terrain, though for a shorter duration and with less-pronounced drying overall...only into the 25-30% range in most spots...as the first hints of moist WAA begin to develop ahead of the next system.

Key message 2: Widespread rain is expected Saturday night through Sunday night. This will mainly be a beneficial rainfall with little to no hydro impacts expected.

By Saturday night, a compact shortwave trough will be located over the Southern Plains with shortwave ridging quickly translating from the Deep South to the Carolinas. Deep-layer southwest flow will overspread the area late overnight into early Sunday morning in the wake of the passing shortwave ridge. A plume of deep moisture with anomalous PWATs of 1.25-1.5" will advect from the Gulf into the Southern Appalachians with modest moisture transport. Meanwhile, progressive surface high pressure is forecast to slide across the Great Lakes region into New England. Initial rainfall falling into a dry sub-cloud layer will help to establish a Cold Air Damming (CAD) wedge with the wedge boundary located generally south of I-85. Widespread moderate to locally heavy rainfall will continue through the day Sunday as isentropic ascent is maximized atop the CAD as the surface low passes by to our south. While the moisture plume will be anomalous, a lack of elevated instability will generally preclude more focused convective rainfall rates. Thus, expected widespread 1.25-1.5" of rain will prove to be more beneficial with very minor to no hydro impacts. The duration of rainfall spread out across the day on top of ongoing D3-D4 drought conditions and low river/stream flows further support a lack of hydro concerns. The 5-10% plume on ensemble hydrographs also struggle to reach action stage. Rainfall will gradually taper off from west to east Sunday night with only a stray lingering shower left by Monday morning. Temperatures will be cool within the CAD wedge with highs Sunday struggling to reach 50 in the hear of the wedge.

Key message 3: Temperatures warm early to middle next week with a return of dry weather.

The synoptic pattern remains progressive with the passing shortwave trough quickly shifting offshore by Monday night. Flat upper riding quickly becomes established with a subtropical ridge centered over the Gulf. An extensive swath of westerlies is progged to extend from the Desert Southwest, across the Plains and into the Appalachians on the poleward side of the ridge. Rising heights and warming low-level temperatures will foster a notable warming trend with temperatures climbing back into the low to mid 70s by Wednesday and Thursday.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: VFR continues for the 12z TAF period. Light NE wind in most places will pick up,climbing to 3-5kts after daybreak, then gradually turn SE through thi sevening. For KAVL winds should remain out of the NNW for most of the period, and could climb to 7-9kts during the afternoon. Light winds expected again tonight, becoming steadier at 5-10kts out of the SW by Saturday afternoon. Expect generally SKC through the period.

Outlook: Dry and VFR through Saturday evening, before precipitation chances and associated restrictions return Saturday night into Sunday. Drier conditions and VFR should return for the beginning of the week.

GSP WATCHES/WARNINGS/ADVISORIES

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