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. The ENE flow will continue to steadily push stable 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 /12Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: MVFR cigs are expanding across mainly the western half of the Terminal Forecast Area this morning. Expect MVFR cigs at the upstate SC terminals and KAVL through at least the morning. Locations farther west (i.e., KAND and perhaps KGMU) may stay MVFR through the day, while only modest improvement to the lower end of VFR is expected at KAVL and KGSP this afternoon. KCLT and KHKY should see low VFR cigs this morning...lifting to 050 or higher during early afternoon. Some scattering is possible at those sites out at times this afternoon.

ENE winds around 10 kts...slightly higher with some gusts at the Upstate terminals at the start of the period will steadily weaken through the daylight hours...becoming light ESE during the afternoon, then light/variable during the evening. Moisture will make yet another return into the area tonight, with Prob30s for SHRA and lowering cigs entering the forecasts (except at KHKY) during Sunday evening. All sites are expected to see MVFR cigs develop by daybreak Monday. IFR is possible at the Upstate terminals.

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.