textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated Aviation Discussion

KEY MESSAGES

1. A potential for locally heavy rainfall and isolated flash flooding continues today. Briefly cooler and drier on Sunday before rain returns Monday. 2. Dry and cooler than normal weather is expected Tuesday through at least Thursday. Slightly warmer with a small chance of diurnal convection Friday.

DISCUSSION

Key message 1: A potential for locally heavy rainfall and isolated flash flooding continues today. Briefly cooler and drier on Sunday before rain returns Monday.

The latest water vapor imagery depicts a short wave trough moving across the Deep South, with a plume of deep moisture extending from the central Gulf northeast through the Savannah River Valley into the southern Appalachians. Weakening areas of showers with a few isolated storms persist within this plume across the western part of our forecast area. Individual cell movement has been relatively progressive, and there hasn't been much cell training observed, but small convective clusters have shown some tendency to back build, while there has also been some anchoring of convection observed along terrain features along the TN/NC border. This has resulted in very isolated areas of very heavy rainfall of 2+ inches. This potential will continue across the high terrain through the morning, and can't rule out a stray flash flood event.

If anything, forecast profiles suggest a slight downtick in the potential for locally heavy rain and flash flooding during the daylight hours, as mean cloud-bearing winds accelerate slightly, and the potential for back building of convective clusters diminishes somewhat. Nevertheless, at least scattered showers and some thunderstorms should persist into the afternoon in the vicinity of weak frontal boundary, and increased instability should keep the low-end flash flood threat going into the afternoon.

By this afternoon, stable air circulating around sprawling surface high pressure building into the northeast quadrant of the country in the wake of a cyclone departing the New England coast will spill southwest down the eastern slopes of the Appalachians, with inverted ridge building into our forecast area by this evening. This will send the surface boundary southwest through the CWA and bring an end to convection for much of the area by the end of the evening. Cool/stable conditions persist into Sunday, with temperatures around 10 degrees below normal forecast for much of the area outside the mountains. Sunday PoPs are limited to the western and southern periphery of the CWA, where some afternoon instability is possible...especially across the mountains closer to the TN border.

Moisture begins to increase yet again Sun night into Monday...between surface high off the Southeast Coast, and ahead of approaching cold front associated with an area of height falls diving from the Great Lakes into the central Appalachians. PoPs will once again ramp up Sunday night and especially Monday. Drying with a little more staying power finally arrives (for the most part) Monday evening. Other than the below-normal temps Sunday, temperatures are forecast to be near-normal through Monday night.

Key message 2: Dry and cooler than normal weather is expected Tuesday through at least Thursday. Slightly warmer with a small chance of diurnal convection Friday.

Anomalously low height are forecast to persist near the East Coast through much of the new work week, maintaining general low level/dry ridging and cooler-than-normal temps through at least Thursday. A short wave trough is forecast to dig down the western periphery of the trough and into the forecast area Tuesday. The latest GFS is especially strong with this feature and responds with a round of convection Tue afternoon. This is generally at odds with the other global models, but it nevertheless seems prudent to advertise a small PoP. Dry weather with temps around 5 degrees below climo are otherwise forecast through Thursday. Temperatures and moisture are forecast to increase to near-normal by Friday, and small chances for diurnal convection are warranted for the end of the week.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: Showers persist across the NC portion of the Terminal Forecast Area this morning. In the immediate near term, shower potential is expected to be confined to the NC TAF sites, and tempos for SHRA (with TSRA at KCLT) are carried there this morning. With some heating anticipated from late morning into the afternoon, scattered TS are expected to develop across the southern half of the area in the vicinity of a east/west oriented cold front and along terrain features. Prob30s for TSRA are carried at the upstate SC terminals as well as KAVL during the afternoon. Outside of tempos, VFR conditions are forecast, albeit with plenty of cigs on the lower side of VFR. However, a brief restriction is possible in low cigs at KAND this morning, where some rain did fall last evening.

Coverage of convection is forecast to wane quickly this evening, as more stable air begins pushing in from on NE winds increasing to 5-10 kts. In the interim, winds are mainly expected to be light SW or light/variable. NE winds may become gusty at the Piedmont terminals by daybreak Sunday. While VFR is forecast at all TAF sites tomorrow morning, there is some potential for fog/low stratus at the upstate SC terminals and KAVL, where the dry air will not be as deep.

Outlook: Drier conditions continue into Sunday before another cold front brings convective chances back Monday. A drier pattern should return for the rest of the workweek.

GSP WATCHES/WARNINGS/ADVISORIES

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