textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Confidence is increasing regarding widespread rain for Thursday.

KEY MESSAGES

1. Gusty winds return tonight into Wednesday ahead of an approaching cold front. Rain chances will also increase ahead of the front on Wednesday, mainly across the mountains. 2. Rain returns to the area Wednesday night through Friday morning followed by warm and dry weather this weekend.

DISCUSSION

Key message 1: Gusty winds return tonight into Wednesday ahead of an approaching cold front. Rain chances will also increase ahead of the front on Wednesday, mainly across the mountains.

A cold front will approach out of the northwest tonight into Wednesday, allowing gusty southwest winds to return. With a 40-45 kt 850 mb jet tracking overhead tonight into early Wednesday morning, and decent mixing expected Wednesday afternoon, blended in some of the NBM 90th percentile for wind gusts on Wednesday. Gusts are still expected to remain below Wind Advisory criteria, ranging from 20 to 35 mph below 3,500 ft and 25 to 35 mph above 3,500 ft. Higher elevations could see gusts from 40-45 mph, but a wind advisory will not be issued as any gusts near advisory criteria (>45 mph) will be confined to the highest ridgetops.

Dry conditions should linger through tonight as high pressure remains in place ahead of the front. Rain chances return across the mountains on Wednesday as the cold front sinks southward and as the surface ridge pushes south and east. The best chances expected along the NC/TN border per the 12Z CAMs. The 12Z HRRR shows the potential for some rain to break containment of the mountains late afternoon or early evening but confidence is low.

Cloud cover gradually increases tonight, allowing lows to end up a few degrees above normal. Despite broken to overcast cirrus lingering through Wednesday, highs will be noticeably warmer thanks to SW flow. Highs on Wednesday should end up near to just above normal for locations east of the mountains and across the French Broad Valley. Elsewhere, highs should remain below normal.

Key message 2: Rain returns to the area Wednesday night through Friday morning followed by warm and dry weather this weekend.

By tomorrow night, broad troughing will encompass most of the CONUS with several embedded perturbations embedded within the mean background flow regime. A loosely defined trough axis is forecast to be situated from the Ohio Valley to the Lower Mississippi Valley with west/southwest flow extending across the Southern Appalachians. In addition, moist southwest 850mb flow will advect a plume of deep moisture into the area with PWATs surging to near 1.25". Precipitation is progged to blossom Wednesday night along the leading edge of the moisture plume across the mountains and much of the foothills. Precipitation will expand in coverage through the day Thursday and will become focused along the leading edge of a frontal boundary sagging into the area from the northwest. The front will become oriented nearly parallel with the upper flow and will be slow to move through the area until the primary trough axis finally swings through Thursday night into Friday morning. This will keep plenty of rain around through much of the late week period. A few hundred J/kg of MUCAPE may prove sufficient for a few rumbles of thunder and perhaps convective elements embedded within the larger precipitation swath. Overall, this will be a beneficial rainfall event given ongoing drought conditions with generally 0.75-1" of rain expected with locally higher amounts over portions of the mountains and western Upstate. A lack of stronger moisture transport and convective rainfall rates should generally preclude any flooding concerns. Conditions gradually dry through the day Friday as the upper trough axis swings east of the area with warm and dry weather returning for the weekend with afternoon highs in the upper 60s to low 70s.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR through at least midday Wednesday. Abundant cirrus will be seen overnight and Wednesday within strong W to NW flow associated with upper jet. These will occur atop SW'ly flow in low levels, and LLWS criteria look to be met at KCLT/KAVL/KHKY generally from 04-06z through 11-14z. As slight veering and strengthening of sfc flow occurs overnight, that should reduce the shear just below mentionable criteria. Hence sporadic occurrences of LLWS may occur outside that window and/or over other sites near daybreak. Gusts look to begin overnight but strengthen above 20 kt during the early daytime hours, peaking at 25+ kt in the early afternoon. Approach of cold front Wed afternoon will introduce small precip chances over the NC mountains, though too low to mention at this issuance. Low VFR to MVFR level clouds will be seen and an MVFR cig prior to 00z cannot be ruled out. At KCLT low VFR clouds should be enough to impact slant range vsby even though MVFR cigs look unlikely until after 06z Thu.

Outlook: Lighter wind speeds return by Wednesday evening. A cold front tracks across the terminals on Thursday, bringing showers and associated restrictions through at least Thursday night. Activity may linger through early Friday before dry conditions return late Friday into the weekend.

GSP WATCHES/WARNINGS/ADVISORIES

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