textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The forecast continues to trend wet and cool, especially through the Memorial Day holiday weekend.

The aviation discussion was updated to reflect the 06Z TAF issuance.

KEY MESSAGES

1. A cold front will drop down from the northwest late today and tonight, ushering in a change in our weather for the Memorial Day weekend. The new pattern will support a period of cooler and more unsettled weather that could ultimately put a dent in our drought as it persists into the middle of next week. At this time, the risk of severe thunderstorms and flooding rain appears low.

DISCUSSION

Key message 1: A cold front will drop down from the northwest late today and tonight, ushering in a change in our weather for the Memorial Day weekend. The new pattern will support a period of cooler and more unsettled weather that could ultimately put a dent in our drought as it persists into the middle of next week. At this time, the risk of severe thunderstorms and flooding rain appears low.

A day of change is in store for the western Carolinas and northeast Georgia as a TUTT low off the Southeast Coast fades away to the southeast and we come more under the influence of better south to southwest flow aloft. Already, we are seeing showers and isolated thunderstorms persisting near the Blue Ridge Escarpment as they take advantage of a light southerly upslope low level flow of slowly increasing moisture. After a quiet week, that should be a clue that changes are underway. The expectation is for the convection to eventually weaken and dissipate by daybreak, after which the balance of the morning would be quiet, allowing for a warmup with temps roughly ten degrees above normal once again by early afternoon, though not as hot as the last few days. By this afternoon, a cold front will be dropping in from the northwest, though without much support aloft. The RAP develops roughly 1500 J/kg of sfc-based CAPE to fuel the development of scattered thunderstorms beginning in the mid/late afternoon but shear will be weak, which should limit how strong the storms get. An isolated severe storm would never be completely ruled out in a situation like this, however. Overall, the precip chances for the day are relatively high, though at any given time the coverage of showers and storms will be scattered, in other words the day is not expected to be a washout.

Once the front slips southward this evening, a sfc high over eastern Canada will nose down east of the mtns and establish a cold air damming wedge across the region by daybreak Friday. Developing low level isentropic upglide early in the day should develop enough low cloudiness to lock in the cooler air mass that will be noticeable compared to our week thus far. For now, our forecast has high temps in the 70s east of the mtns, undercutting what is in the NBM by several degrees, but that could easily be ten degrees too warm if we end up with extensive light rain. The new guidance suggests the wedge is likely to persist through Saturday even as the transitory parent high moves off the Canadian Maritimes. Temps were once again lowered from the model blend. Support for CAD fades Sunday as the southwesterly flow aloft increases.

From that point onward, unsettled weather will continue as the Gulf remains open with a mean upper trof axis over the srn Plains/MS Valley region and a mean ridge off the East Coast. So, from Memorial Day onward, we are looking at a favorable period of above climo precip probs and rainfall coverage. If this persists as indicated by some guidance, we could eventually get to the point where flash flood risk creeps upward, but for now we will manage expectations.

AVIATION /06Z THURSDAY THROUGH MONDAY/

At KCLT and elsewhere: Dealing with some lingering light rain at KAVL for the first hour that may inflict an MVFR vis restriction. The rain increases the chances of restrictions persisting or redeveloping in the pre-dawn hours. For now we revert to VFR at 07Z, but expect this to be amended based on trends. Otherwise, VFR at the other terminals until this afternoon when new convection develops. The CAMs have scattered coverage for the most part through the early evening, so we continue to opt for PROB30 groups to contain the TSRA chances and associated restrictions. Wind will be mainly SW and light through the afternoon. At some point this evening, a frontal boundary will drop south across the fcst area, so wind may go variable until the boundary passes, at which point it goes NE and the cold air damming wedge develops. Flight restrictions will develop quickly behind the wedge boundary, down to MVFR in late evening and IFR in the early morning hours.

Outlook: Cold-air damming across the area by daybreak Friday, and may persist thru Saturday. The CAD will likely produce widespread MVFR to IFR ceilings through the day Friday and into Saturday. Periods of mainly diurnal convection will also continue atop the CAD wedge and into next week, even as the CAD erodes. The potential for overnight fog/low clouds will increase through the period as well.

GSP WATCHES/WARNINGS/ADVISORIES

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