textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated Aviation Discussion.

KEY MESSAGES

1. Scattered showers and thunderstorms develop this afternoon, with a marginal risk for severe storms, mainly across the southern half of the area. Temperatures rebound to near-normal today, with a return to cooler conditions Tuesday. 2. Dry conditions are expected from Wednesday through Saturday. A warming trend begins Wednesday, with a return to near-normal temperatures expected by the weekend.

DISCUSSION

Key message 1: Scattered showers and thunderstorms develop this afternoon, with a marginal risk for severe storms, mainly across the southern half of the area. Temperatures rebound to near-normal today, with a return to cooler conditions Tuesday.

The inverted surface ridge has dissipated almost as quickly as it developed, with surface winds having become light/variable or calm across the entire area. Nevertheless, low clouds remain widespread this morning. Surface analysis depicts a weak wave centered just off the SC coast. As this develops a bit more through the morning, the flow above the surface is expected to become NW and increase to 15-20 kts. Downslope effects should make rather quick work of much of the cloud cover later this morning, and this is expected to allow temps to warm to near-normal this afternoon, with surface moisture becoming sufficiently elevated to modestly destabilize the atmosphere (sbCAPE 1000-1500 J/kg). Meanwhile, yet another area of transient high pressure will begin spilling into the northeast quadrant of the Conus this morning, with yet another inverted ridge building south to the east of the Appalachians throughout the day. The leading edge of this effective boundary will likely reach our northern zones this afternoon. The boundary and terrain effects should provide the impetus for scattered convective development this afternoon, with general 30-50 PoPs advertised for much of the CWA. Deep layer shear increasing to 30-40 kts suggests an uptick in the threat for an isolated severe storm with this activity. However, the more likely scenario for a severe weather event or two will involve the potential for an organized complex of storms originating from the central Conus to make a run for southwest NC and the Savannah River Valley this evening...as depicted in some high resolution guidance sources. There's plenty of uncertainty regarding this scenario at the current time, but even if it occurs, the parameter space is expected to be barely supportive of severe weather in our area.

Cooler/more stable air make a return tonight/Tuesday, with Tuesday's max temps forecast at a solid 10 degrees below today's forecast. Nevertheless, a rather strong short wave is forecast to dig down the western periphery of a long wave trough centered along the East Coast tomorrow afternoon. Cold trough aloft could allow for some convection (almost exclusively showers) to initiate over the mountains. Meanwhile, weak surface development is also possible along the baroclinic zone south of our area...which could allow for some upglide and stratiform-y rain to develop across ~the southern third of the area. 20-40 PoPs are carried across much of the CWA Tuesday.

Key message 2: Dry conditions are expected from Wednesday through Saturday. A warming trend begins Wednesday, with a return to near-normal temperatures expected by the weekend.

Temperatures remain comfortably below normal Wed under anomalously low heights aloft, with depleting moisture/stable conditions resulting in the first CWA-wide PoP-free day in more than a week. Heights will rise aloft through the latter half of the week, allowing temps to steadily warm toward early June normals by Friday/Saturday. The upper air pattern will become static, with an anticyclone that is forecast to meander from the mid-Miss Valley during mid-week to the Southeast by the weekend. This will support persistent surface ridging across our region, with major moisture sources being more or less closed for business. As such, it appears that it will be at least next Sunday before diurnal convective chances return.

AVIATION /12Z MONDAY THROUGH FRIDAY/

At KCLT and elsewhere: MVFR cigs have been clearing in the foothills over the past 1-2 hours in response to a developing downslope flow, with KGSP and KGMU recently seeing their cigs scatter out. It may take another hour or two for the lower clouds to scatter out for good, so at least tempos for MVFR cigs are carried at the Upstate terminals and KCLT through 13/14Z. KAVL is a little trickier, as some IFR level clouds have been floating in and out there throughout the morning. The race against sunrise is on...so do not anticipate any IFR conditions lasting there, but will feature prevailing MVFR cigs and SCT IFR layers through 14Z. KHKY should remain VFR through the period.

All sites should see VFR by late morning, with SCT cumulus in the 030-050 range remaining possible into the afternoon. Scattered convection is expected to develop this afternoon...primarily due to terrain effects...all TAFs feature a Prob30 for TSRA at some point this afternoon, except for SHRA at KHKY. Convective chances diminish overnight with prevailing VFR expected. Winds turn the dial from light SW this morning (except NW at KAVL), to NW at all sites by early afternoon, then light NE this evening. NE winds increase toward 10 kts overnight east of the mountains as a surface ridge builds southwest over the region. Some gusts in the 15-20 kts range are possible Tue morning.

Outlook: Showers are again possible Tuesday. A drier pattern sets up by Wednesday and continues through the rest of the week.

GSP WATCHES/WARNINGS/ADVISORIES

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