textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The forecast continues to trend cooler for late this week and wetter through the early part of next week.

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

KEY MESSAGES

1. A cold front will approach the area today and then stall nearby through the weekend, resulting in cooler and wetter weather through Memorial Day weekend. The threat for severe thunderstorms and excessive rain appears to be low at this time.

DISCUSSION

Key message 1: A cold front will approach the area today and then stall nearby through the weekend, resulting in cooler and wetter weather through Memorial Day weekend. The threat for severe thunderstorms and excessive rain appears to be low at this time.

One more seasonally hot day today, then the forecast gets more uncertain. The situation today looks similar to yesterday as the western Carolinas are under a col region of sorts, resulting from the TUTT low north of the Bahamas superimposed on the old upper ridge deamplifying off the East Coast. Meanwhile, a cold frontal boundary will be making slow progress east of the OH Valley and over the TN valley region. The upshot is that we won't have much in the way of support for deep convection or buoyancy through tonight, at least not east of the mtns. There will probably be enough differential heating over the mtns to support some shower activity, especially in light of the isolated development yesterday, so a chance was kept there. The showers should taper off within a few hours of sunset. Plenty of sun and a lack of convection should allow us to get about ten degrees above normal again, but the air mass remains dry enough to prevent any real heat problems.

Thursday should be the transition day as the guidance moves the old cold front into our region even as mid/upper ridging tries to rebuild overhead. Guidance indicates that southwest flow aloft will become better established which should help provide more fuel while the frontal boundary provides more focus. Temperatures are a concern. Highs are forecast to be 5-10 degrees above normal again because the convection doesn't really get going until mid/late afternoon, but if that were to begin by midday, temps might not get as warm as expected. The overall risk for severe thunderstorms and heavy rain appears to be relatively low, but Thursday probably has the best shot of any day upcoming because of better sfc-based CAPE which tops out around 2500 J/kg and some weak southwesterly shear. Because of the convective nature of the expected precip, some will win and many will lose.

The expectation is that the boundary will be pushed south across the fcst area Thursday night by high pressure moving across the Great Lakes. This transitory sfc high to our north will support a cold air damming wedge for at least Friday, dropping our temps ten degrees or more. The CAD signal appears stronger with this cycle. Some of the guidance has temps struggling to get out of the 60s in the typical wedge areas and that could happen if sufficient low level isentropic lift develops. Note that several of the models do just that and the raw model temps support undercutting the NBM substantially, so the expectation is that our high temp for Friday will drift cooler. Precip probs climb into the likely/categorical ranges and seem to stay there through the holiday weekend and don't improve until the middle of next week. The latest guidance supports this idea with a prolonged moisture flow from the Gulf because of a favorable mean trof/ridge pattern. Expectations should be managed at this point, but if the models stick with this idea, we could actually see enough rain to be beneficial across some parts of the region over the five day period. The QPF has been increased. At any rate, the drought shouldn't get any worse.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

At KCLT and elsewhere: VFR should prevail at all terminals through the period, but there are few details worth mentioning. First, we will be on the lookout for low stratus moving up from the Coastal Plain around daybreak, though it is not nearly as extensive as it was this time last night. Second, scattered showers/storms may develop over the mountains this afternoon, though the latest model guidance keeps storms more isolated than we have in our forecast. Will maintain a PROB30 at KAVL anyway until there is more confidence in it not happening. Otherwise, light/variable wind through sunrise will become light SW to S once again, and a few stratocu are expected. Wednesday night should be quiet again, but clouds will start to increase late.

Outlook: An approaching front and increasing moisture will bring a more active pattern for mainly afternoon and evening showers and thunderstorms beginning Thursday afternoon and then continuing through the end of the week. Cold-air damming may produce widespread MVFR to IFR cigs thru the day Friday. The potential for overnight fog/low clouds will increase through the period as well.

GSP WATCHES/WARNINGS/ADVISORIES

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