textproduct: Greenville-Spartanburg

SYNOPSIS

Drier conditions return behind a departing cold front tonight, and persist into early next week as high pressure builds into the region. Another cold front may bring precipitation chances back Wednesday into Thursday, but forecast confidence remains low at this time.

NEAR TERM /THROUGH TONIGHT/

As of 1253 AM Sunday:

Key Message 1: Gusty winds through today may lead to isolated power outages and difficult travel, especially at higher elevations.

A cold front analyzed just east of the Blue Ridge as of 05Z will make steady eastward progress through the overnight hours and will likely be to the east of the fcst area by daybreak. Cold advection developing behind the boundary will keep the boundary layer stirred up and should allow for relatively deep mixing through the afternoon hours. Fcst soundings show the potential to tap into some winds around 35 kt at the top of the mixed layer east of the mtns, but stronger gust potential closer to 40-45 kt across the high ridges and mountain tops. The new guidance is aligned with the Wind Advisory that we have at elevations above 3500 feet starting at 11Z and running through the end of the daytime period. Note that our gust potential this afternoon will be on the order of 30 kt east of the mtns, not quite high enough to consider a Wind Advisory, but contributing some concern for...

Key Message 2: A conditional fire weather concern exists this afternoon across the area along and south/east of a line from Elberton to Laurens, Union, Rock Hill, and Concord.

Unfortunately, the rain never really reached the southeast fringe of the forecast area on Saturday, so the area southeast of the aforementioned line remains very dry. With the deep mixing this afternoon, the RH is expected to drop down to at least the 30-35 percent range. It wouldn't take much of a forecast error in dewpoint to get some locations that have an RH that falls down into the middle 20s. Thus, a conditional fire weather risk could develop across the area from the lower Piedmont to the southeastern edge of metro Charlotte this afternoon. Ensemble guidance used in the NBM often struggles with post frontal mixing regimes, leading to a high dewpoint and RH bias. Experimental HREF joint probabilities of RH at or below 25 percent combined with wind gusts of at least 30 mph remain low, generally 10 percent or less, suggesting that Red Flag headline criteria are unlikely to be met. But, we will continue to monitor.

SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/

As of 1159 PM EST Saturday...

Key Message #1: Dry and quiet weather expected through the first half of the new workweek.

Still expect mostly quiet weather on Monday and Tuesday as broad, ill-defined high pressure expands across the Southeast. By Monday afternoon, surface flow should begin to pick up out of the southwest, with weak westerly low-level flow supportive of WAA. Given fairly weak flow, however, highs on Monday will rise scarcely a category warmer than on Sunday, only climbing to around 50 for most of the forecast area. Bitterly cold conditions are expected again Monday night as another night of excellent radiative cooling sets up, before somewhat stronger WAA picks up on Tuesday, boosting highs into the mid- to upper-50s across the low terrain. Lows should be considerably warmer Tuesday night owing to the combined effects of strengthening WAA and increasing moisture/cloud cover.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

As of 1212 AM EST Sunday...

Key Message #1: Confidence remains low on the potential for

The pattern should begin to amplify mid-week as successive z500 speed maxxes dip out of central Canada into the Midwest...resulting in the development of a deep, elongated trough easing into the Ohio Valley late Wednesday. The associated surface pattern will be quite complex, with a baroclinic zone developing just east of the forecast area on Wednesday afternoon, and a distinct coastal front setting up along the NC-SC coastline. The trough will first interact with the baroclinic zone to our west, producing an open wave (or perhaps, as in some GEFS solutions, a closed low) along the frontal boundary as it pushes into the western Carolinas. Activation of the coastal front won't take place until later - Wednesday night or early Thursday, at which point rapid cyclogenesis is still expected to take place.

The result, unfortunately, is a highly-uncertain forecast scenario. On the one hand, the first low looks an awful lot like a typical clipper low; indeed, the operational GFS and ECMWF both depict precipitation associated with the advancing trough escaping the northern Blue Ridge and expanding into the NC Foothills and upper Piedmont. However, the presence of the coastal front presents a unique complicating factor: under normal circumstances, the moisture needed to produce precip outside the mountains would need to come from the Atlantic, but the coastal front should function essentially as a moisture sink...keeping much of that moisture from making it far enough west to impact us. Such a drier solution is depicted in the operational GDPS, as well as many of the CMC-GEPS ensemble members. The good news is that whatever precipitation does develop should be temperature-dependent rain or snow - with little if any potential for ice based on current model data.

Key Message #2: Moisture increases early next weekend ahead of an approaching cold front.

Following the departure of the frontal system on Thursday and the ensuing CAA on Thursday night, a progressive surface high should migrate across the region on Friday. The upper pattern should remain unsettled, and by Saturday, we'll already be back in a SW flow regime as the next disturbance - a negatively-tilted, southern- stream vort axis - pushes into the Southeast.

And guidance has a poor handle on this new system so far. There's decent agreement that a cold front will approach the area by the end of the D7 forecast early Saturday...but timing remains in question. Some of the more aggressive ensembles bring precipitation into the NC mountains as early as daybreak Saturday...but the majority of guidance keeps us dry until after the end of the seven-day forecast.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: The cold front was located just east of the Blue Ridge at issuance time, so the first order of business will be the wind shift to the WNW and NW in the overnight hours. All terminals should be some sort of NW by the start of operations this morning, with occasional gusts continuing as the cold advection behind the front takes hold. The front should effectively sweep the remaining MVFR-level stratocu from the western Piedmont and northern Upstate long before operations ramp up in the pre-dawn hours. Once that cloudiness is moved to the east, VFR conditions will prevail for the remainder of the period. Frequent wind gusts from the NW will continue through the daylight hours and should finally abate an hour or so after sunset as the boundary layer decouples.

Outlook: Expect dry VFR conditions for the first half of the week with sfc high pressure over the region. Another frontal system will approach on Wednesday and may bring showers and associated restrictions. Some wintry precip could affect KAVL early Thursday morning.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Wind Advisory from 6 AM this morning to 6 PM EST this evening for NCZ033-048>053-058-059-062-063. SC...None.