textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated for 00z aviation discussion.

Precipitation amounts have dropped slightly for Saturday. Slight rise in low temps for Saturday night slightly increases uncertainty about frost across the mountains early Sunday.

KEY MESSAGES

1. Rain chances increase tonight and peak Saturday morning. They taper off Saturday afternoon with showers moving east of our area by the early evening. Temperatures will remain well-below normal today and Saturday. 2. Cool temperatures across the mountains Saturday night will raise the potential for frost early Sunday morning. Precautions may need to be taken to protect sensitive plants. 3. Another cold front may bring rain to the area during the middle part of the week, but the chances for significant rain or severe storms remain low.

DISCUSSION

Key message 1: Rain chances increase tonight and peak Saturday morning. They taper off Saturday afternoon with showers moving east of our area by the early evening. Temperatures will remain well-below normal today and Saturday.

A large, upper low will remain nearly stationary just north of the Great Lakes today and Saturday. The backside of the low will amplify over the central CONUS on Saturday, moving an upper trof over our area late Saturday into Sunday. At the sfc, a quasi- stationary front will remain over the Gulf Coast as weak high pressure moves offshore today and tonight. Low-level flow will veer to SLY this afternoon in advance of the digging trof to our west. A shallow layer of moist upglide will persist over the dry sfc airmass, maintaining some stratus over at least the southern portion of our fcst area. Some of the CAMs continue to develop light showers near/south of I-85 this afternoon/evening, but any precip amounts would be minimal at best. High temperatures will struggle to reach 70 degrees today across most of our area.

A weak southern-stream h5 shortwave will help to activate a warm front this evening bringing moist upglide northward toward our area tonight. The deeply saturated layer and dynamic lift from the shortwave spread showers northward and into our CWA overnight and into Saturday morning. The precip will move east of our area by the early afternoon, with a few trailing showers possible over the Upstate thru the evening. It still appears that the best QPF response will be to our SE, with most of our CWA seeing less than 1 inch of total rain, and the mtns/northern foothills and Piedmont less than 0.25 inches. Profiles still appear unfavorable for con- vection to develop, but I wouldn't rule out a few lightning strikes south of I-85.

Although Saturday's sfc pattern does not feature a typical CAD-type sfc high, the dry sfc layer at the onset of precip should allow for a fair amount of diabatic cooling. Thus, we could see a notable drop in temperatures early Saturday morning (resulting in lows slightly below normal), which may not change much while the precip is ongoing. The lack of a true CAD should allow for some warming Sat afternoon as the precip ends. Nonetheless, highs will likely remain around 15 degrees below normal.

Key message 2: Cool temperatures across the mountains Saturday night will raise the potential for frost early Sunday morning. Precautions may need to be taken to protect sensitive plants.

Once a deepening sfc low departs to the northeast late Saturday, we are on track to build in a cool and dry air mass once the mid-level trof axis swings thru Saturday evening. Across the mountains, the issue will be the low temp forecast early Sunday morning, which continues to show elevations above 6k feet getting down below 32F, and elevations above 5k feet having a greater than 30 percent chance of dropping below 32F. That being said, the new forecast actually bumped up the low temp fcst by a degree or two across the mtns, and there is still the issue with some NW flow upslope cloudiness potential. A Freeze Warning would not be issued in this situation because of the lack of agriculture and people living above 5k feet, with the possible exception of Avery County. Too much uncertainty is present to entertain a Freeze Watch. However, a Frost Advisory is a distinct possibility because even the populated valleys should get cold enough for frost with some confidence. There are factors working against it, including the aforementioned upslope cloudiness, and the pressure gradient keeping enough wind across the region to prevent much in the way of frost forming. Fortunately, we have another cycle to consider before making a decision, but tune in Saturday to check on the forecast and see if any preparations need to be made to protect your plants if you live in the mountains.

Otherwise, temperatures will remain around ten degrees below normal for the rest of the weekend as the surface high settles over the Southeast.

Key message 3: Another cold front may bring rain to the area during the middle part of the week, but the chances for significant rain or severe storms remain low.

The first half of next week looks benign as high pressure moves across the Southeast, supported by the confluence of split flow upper pattern. Temps should return close to normal by Tuesday as the sfc high slips eastward off the East Coast. By mid-week, confidence is low as to how the srn and nrn streams come back into phase, which would affect the timing and strength of a cold front that for the moment is pegged for Wed/Wed night. The new run of guidance keeps buoyancy ahead of the front to a minimum, so severe storms don't look like a problem at this point. Although the position of the sfc high offshore and the mid/upper trof axis to our west ahead of the front is favorable for Gulf moisture return, right now this looks to be only beneficial as the chances for more than an inch of rain are at best only around 30 percent. We will monitor the guidance trends.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR conditions will continue through the evening and into the overnight before ceilings lower and rain moves back into the region. High clouds will persist as a storm system slides along the Gulf Coast. With time, moisture will increase across the area with ceilings lowering and a band of light rain reaching into the I-85 corridor. How far north rain makes it is uncertain, but Asheville appears to miss out on the action with Hickory on the edge. The I-85 terminals from AND through GMU/GSP to CLT appear to be more of a lock. A several hour period of MVFR ceilings may also accompany this activity and an instance or two of IFR cannot be discounted either. Rain will shift out of the area by the early afternoon hours with a return of VFR conditions.

Outlook: Dry/VFR conditions return by Sunday and linger through at least Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

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