textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Precip chances have been increased for Tue afternoon.

KEY MESSAGES

1. Cooler and dry for much of the area today, with rain chances increasing from the south again tonight into Monday. The potential for locally heavy rainfall will continue, while a slight increase in the threat of severe storms is expected Monday. 2. Cooler than normal weather is expected during mid-week, with a warming trend expected beginning Thursday. Otherwise, mostly dry conditions from Tuesday onward.

DISCUSSION

Key message 1: Cooler and dry for much of the area today, with rain chances increasing from the south again tonight into Monday. The potential for locally heavy rainfall will continue, while a slight increase in the threat of severe storms is expected Monday.

The leading edge of a frontal boundary has pushed southwest of the forecast area early this morning, while E/NE flow is strengthening in response to an inverted surface ridge. Still...enough moisture and instability linger across the southwest part of the CWA to allow for isolated convection across the Savannah Valley, with some locally heavy rainfall occurring due to slow cell movement and back-building of small cell clusters. This activity will continue to steadily diminish in coverage and intensity through daybreak. The ENE flow will steadily push deeper dry air into the area this morning, and much of the CWA will see conditions free of precip trough the daylight hours. The exception will be around the southwest and western periphery of the area, where the dry air will not be as deep, and some instability could be realized (mainly in the area around thew Smokies.) Even in these areas, PoPs are only in the 20-40% range this afternoon. Weak instability and mean cloud-layer winds increasing to 15-20 kts will limit any excessive rainfall potential, but isolated heavy rain is still possible. High temps are expected to be 5-10 degrees below climo from the foothills/Blue Ridge into the Savannah Valley, where cloud cover is expected to be more persistent. Deeper dry air across the eastern zones should result in highs closer to normal, while highs across the mountains and surrounding valleys bordering TN (displaced from the NE flow) may see above-normal max temps.

The first in a series of height/low level pressure falls is forecast to approach the region from the TN/OH Valley tonight, weakening the surface ridge and allowing flow to turn to the SSW across the area this evening. A weak surface wave is forecast to develop across the coastal plain tonight. This will occur close enough to the CWA to allow PoPs to ramp up to the solid chance-to-likely range tonight across the southern half of the area overnight. The threat for locally excessive rainfall along with a low end flash flood threat will continue.

The next round of (more substantial) height falls for the region is slated for Monday, when a strong short wave trough is forecast to dig south from the Great Lakes toward the central Appalachians. This will enhance the potential for diurnal convection across our area Mon afternoon, with PoPs mostly in the 50-60% range advertised. With the long wave trough expected to retrograde from the western Atlantic in response to height falls, mid-level wind fields/shear parameters are expected to improve sufficiently to support a risk for severe weather Monday afternoon, although expected modest instability is expected to keep the threat to the marginal end of the spectrum. Temperatures are forecast to be right around normal Sunday night through Monday night.

Key message 2: Cooler than normal weather is expected during mid-week, with a warming trend expected beginning Thursday. Otherwise, mostly dry conditions from Tuesday onward.

Sprawling high pressure centered over the Great Lakes will build into the forecast area Mon night into Tue under anomalously low heights. Despite this, guidance is arriving at more of a consensus that scattered showers will develop Tue afternoon as cold trough aloft passes over the region. PoPs mostly in the 30-40% range are advertised during this time. Dry conditions are otherwise forecast for much of the remainder of the week as general surface ridging persists with modest-at-most moisture recovery anticipated. Temps are forecast to be 5-10 degrees below normal Tue night through Wed night before recovering to near-normal by Thursday. The steady warming trend will continue into the weekend, with above-normal temps forecast by next Saturday.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Isolated showers linger across the southwest portion of the Terminal Forecast Area early this morning, but are unlikely to impact any of the TAF sites...VCSH at KGMU and KAND should cover it. Otherwise, increasing ENE surface winds associated with an inverted ridge will gradually filter in drier air from the east through the morning...and this is expected to result in continued VFR conditions at KCLT and KHKY through the daylight hours. Closer to the leading edge of the ridge (i.e., upstate SC), MVFR cigs are likely to develop toward daybreak, and this is handled with a tempo prior to daybreak...becoming categorical around sunrise and continuing through the morning. At KAVL, a wet ground is resulting in some concern that fog/low stratus could develop there by daybreak, as the drier air may take some time to filter into the mountains. Have opted for MVFR conditions for the time being. Having said that, can't rule out IFR (or lower) conditions at KAVL, or the Upstate terminals for that matter. This potential is handled with SCT IFR cloud layers within tempos. While some improvement in cigs is expected at the western sites this afternoon...cigs are expected to remain at the lower end of VFR through the afternoon.

NE wind will become gusty at KCLT and the Upstate terminals by around daybreak, then steadily weaken through the daylight hours...possibly becoming light ESE during the afternoon, then light/variable during the evening. Moisture will make yet another return into the area late in the forecast period, with Prob30s for SHRA and lowering cigs entering the forecasts (except at KHKY) during Sunday evening.

Outlook: Shower and possible thunderstorm chances remain elevated into Monday. Another round is possible Tuesday, but this is more uncertain. A drier pattern should set up by Wednesday and continue through the rest of the workweek.

GSP WATCHES/WARNINGS/ADVISORIES

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