textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for the 00Z Aviation Discussion.

KEY MESSAGES

1. Dry air will move in behind a cold front for Tuesday, with some locations seeing RH down to 30 percent in the afternoon. 2. Another weak cold front may bring a few more showers and thunderstorms to the western Carolinas Wednesday. Dry and briefly cooler Thursday and Thursday night, followed by a warming trend Friday through the weekend.

DISCUSSION

Key message 1: Dry air will move in behind a cold front for Tuesday, with some locations seeing RH down to 30 percent in the afternoon.

A cold front will continue to sag southward tonight. There remains a small chance of a shower through mid-evening, mainly in northeast GA and the western Upstate, but otherwise, abundant mid to high altitude cloud cover will linger through the evening. Clearing should occur from N to S late in the night. Drying will occur only slowly at the surface, and as winds turn light in the northern CWA, some fog or low stratus may develop there. Sunnier skies Tuesday should result in max temps trending a few degrees warmer compared to Monday in our northern zones, but a little cooler in the south. Drier dewpoints will mix down to the surface across the area Tuesday and some locations will see RH dip to near 30% by mid-afternoon.

Key message 2: Another weak cold front may bring a few more showers and thunderstorms to the western Carolinas Wednesday. Dry and briefly cooler Thursday and Thursday night, followed by a warming trend Friday through the weekend.

Deep shortwave will begin to cut off over the Great Lakes Wednesday; while the best DPVA looks to occur to our north, height falls occur over our area as a result, and a cold front will approach the southern Appalachians during the day. Moisture return ahead of the front appears limited, partly owing to the good mixing/drying expected Tuesday, and veered low-level winds Tue night and early Wed. Nevertheless, models generally still do depict a narrow band of above-normal PWATs advecting into the area just prior to the fropa, with similar peak values in our Piedmont, though varying in the timing of that peak. The 12km NAM and its typically similar Canadian model are more aggressive in bringing Gulf air above the boundary layer early Wed morning, and accordingly are appreciably higher with afternoon dewpoints and SBCAPE than the GFS/EC operational models. LREF probs of 500 J/kg SBCAPE have actually decreased in our CWA on the latest available cycle, but that appears to be related to a slightly earlier depiction of the fropa. Not much change in NBM PoPs versus the overnight cycle, which seems reasonable in light of model spread mainly being in timing and little change in CAPE potential. LREF still shows mean values of 50-60 kt sfc-500mb bulk shear, with even the 10th percentile being near 40 kt. If the front ends up being timed to induce convection east of the mountains near peak heating, and we manage the higher-end CAPE, we could be looking at a low-end severe threat Wednesday afternoon, mainly for damaging wind, with potential for some linear organization. The moisture/CAPE still appears the limiting factor.

Between the cutoff low over the NE CONUS, and upper ridge in the lower MS Valley, along with CAA, gusty NW winds develop in the wake of the front Wednesday night over the mountains and skies clear. Temps trend noticeably cooler for the mountains Thursday, but downsloping appears to offset that trend for the Piedmont. Dewpoints look to tank across the CWA, with continuing gusts likely. Winds decline Thu night into Fri morning as sfc high shifts over the area from the NW. The enhanced radiational cooling conditions potentially will bring morning mins around 10 degrees below normal; some portions of the mountains could dip into the upper 30s, but probably still too warm for frost. Temps rebound a bit Friday as upper low departs and heights rise under mostly sunny skies.

Another low will pass north of the Great Lakes Saturday, which could bring another weak front into the lower OH and TN valleys, reflected in the return of small PoPs to the mountains then and Sunday. However, assuming cloud cover or precip does not impact temps, temps remain on an upward trend, particularly Sunday. Max temps Sunday may hit 90 in a number of spots.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Satellite imagery shows persistent stratocu decks at multiple levels, but mostly VFR, with mid and high clouds streaming over the top of that. Expect VFR to prevail at all terminals through the early morning hours, but at some point before dawn we will be on the lookout for the development of an IFR/LIFR stratus ceiling over western NC. At the moment, only KHKY has a good shot, so they get an LIFR ceiling in a TEMPO group around daybreak, and we will go from there. Wind will be mainly NE overnight. After daybreak, if the low clouds develop they should scatter, lift, and mix out by mid-morning. From that point onward, only scattered cirrus is expected. Wind should come around to SE as sfc high pressure moves off the Mid-Atlantic coast.

Outlook: Dry conditions persist through Wednesday morning. A clipper-type low may cross to our north late Wednesday, but guidance suggests rainfall will be paltry with this system, and it's questionable whether any flight restrictions will develop.

GSP WATCHES/WARNINGS/ADVISORIES

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