textproduct: Greenville-Spartanburg

SYNOPSIS

Precipitation returns tonight, resulting in a wintry mix across the North Carolina mountains and Foothills. Precipitation chances and below-normal temperatures linger through the first part of next week. Temperatures trend back toward normal by mid-week. Another cold front may bring precipitation back to the area Thursday.

NEAR TERM /THROUGH FRIDAY/

As of 100 PM EST Thursday...

Key Messages:

1) Wintry precip expected across the NC mountains and even parts of the NC Foothills tonight into Friday morning...with a mix of snow and freezing rain expected in the mountains, and mainly snow expected in the Foothills.

2) Winter Weather Advisory remains in effect from 7PM this evening through Friday morning for portions of the NC mountains (no changes from previous forecast).

3) Precip will change over to rain and will taper off by early Friday afternoon, but cold and cloudy conditions will continue

A southern stream upper-level shortwave trough will become sheared out as its energy merges with a northern stream trough currently crossing the Great Lakes. This energy will strengthen an upper jet streak over the Mid- Atlantic, which will support some upper divergence atop the forecast area tonight into Friday. The southern stream jet will continue to spread a lot of mid and upper moisture across the region, maintaining a thick cirrus shield thru the rest of the day. Even spotty light rain or sprinkles may reach the ground in the far southern part of the forecast area, but no measurable amounts expected thru sunset. Temps may struggle to get into the 50s across most of the area this aftn as a result of the clouds.

Tonight, the center of a 1030 mb sfc high pres will track into Upstate NY and weaken as it reaches the New England coast by late Friday. The high will be in a good position to produce a hybrid cold air damming wedge into the Carolinas. Meanwhile, cyclogenesis will occur along the central Gulf Coast and spread frontogenesis and isentropic lift along a stalled frontal boundary across the Southeast. The low will quickly track east along a baroclinic zone to the Carolina Coast overnight. Forcing doesn't look appreciably strong, so QPF is expected to be light, but categorical PoPs look on track for the overnight thru early Friday morning. Low- level thicknesses are a little colder than the previous winter wx event, allowing for more snow and sleet to start out this evening into the overnight across the higher elevations. A warm nose will punch in from the SW and change precip over to mostly rain and freezing rain by daybreak Friday. No big changes were seen in the latest guidance on temps or QPF, so the current Winter Weather Advisory looks good. In addition to the mountains, up to half an inch of snow may accumulate out across the foothills and NW Piedmont north of I-40, but should change over to rain by mid-morning Friday. Impacts from this don't seem to warrant expanding the advisory at this time. Temps will lock in the upper 20s to lower 30s in the high elevations and along the eastern NC Escarpment, and mid to upper 30s elsewhere.

By midday Friday, the upper shortwave will exit to our east and take the better isentropic lift with it. Sfc low pressure will begin to deepen near the Outer Banks, but a residual CAD wedge will linger thru the rest of the day. Precip chances taper off from NW to SE, but low clouds and fog will persist, keeping temps in the upper 30s to mid 40s for most of the area. All but the highest ridges of the northern mountains are expected to get above freezing by the end of the day.

SHORT TERM /FRIDAY NIGHT THROUGH MONDAY/

As of 1210 PM Thu:

Model guidance has trended drier in the wake of the departing low pressure system Friday night into Saturday. That said, another low pressure center moves east along the stalled frontal boundary to our south. This will bring a return of some moisture and weak forcing, however; this will mainly be limited to NE GA and the Upstate with some slight chances for NC. Even with the lingering cold air, this will help limit the chance of any wintry precip to the highest elevations of the NC mountains, with no significant additional accums expected.

The stalled frontal boundary does move south Saturday night, but yet another wave of low pressure spins up and moves east along the front. A northern stream short wave also moves into the area bringing an increase in moisture and forcing. The Canadian model has trended significantly drier with this system, while the GFS and ECMWF remain on the dry side. This is due to the surface low being farther south and less interaction with the northern stream short wave limiting moisture return into the area. Still, there is enough moisture and forcing for chance PoP to return Sunday and Sunday night. Temps look to be warm enough for just rain for all but the higher elevations of the NC mountains where any wintry precip would be snow. There could be a decent period of snowfall for the higher elevations, but it's too early for good confidence on any accums. Precip chances taper off quickly Monday as the low and short wave move east of the area.

Lows near normal Friday night rise a few degrees by Sunday night. Highs 5 to 10 degrees below normal Saturday rise a few degrees on Sunday, then fall back to around 10 degrees below normal Monday.

LONG TERM /MONDAY NIGHT THROUGH THURSDAY/

As of 1230 PM Thu:

Quasi-zonal flow develops on Tuesday with southwest flow developing late Wednesday ahead of a northern stream short wave diving toward the area. The short wave crosses the area late Wednesday night or Thursday. At the surface, high pressure settles over the area Tuesday then moves east Wednesday. A cold front crosses the area late Wednesday night or Thursday. Moisture and forcing do increase with the front, but there is no significant Gulf or Atlantic inflow ahead of the front. Also, the air mass moderates significantly Wed into Thu as the high moves east well out of cold air damming range. This will help keep precip as rain for all but the higher elevations of the NC mountains where precip may begin as or mix with snow with some additional northwest flow snowfall after frontal passage on Thursday. Accumulations are possible but too early for any specifics.

Lows around 10 degrees below normal Monday night rise to slightly above normal by Wednesday night. Highs Tuesday around 10 degrees below normal rise to around 5 degrees below normal for Wednesday and Thursday.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

At KCLT and elsewhere: VFR this aftn into early evening, with thick mid and high clouds and light wind. Conditions will begin to deteriorate from west to east after sunset, as rain steadily pushes in across the area and leads to a quick reduction in flight category from VFR to at least IFR everywhere by daybreak Friday. A mix of rain and snow is expected at KHKY for part of the early morning hours Friday before changing to all rain by mid-morning. Cannot rule out a wintry mix at KAVL when precip first starts tonight, but should become all rain fairly quickly. Light rain will begin to taper off from NW to SE toward the end of the 18z TAF period. But a lingering wedge will keep IFR to LIFR cigs and MVFR to possibly IFR vsby into Friday aftn across the area. Winds will pick up out of the NE as the wedge forms this evening, but expected to remain under 10 kt.

Outlook: Widespread low stratus and fog is expected Friday night thru early Saturday. A brief break in restrictions is expected Saturday, but another storm system may bring some precip chances and low clouds Sunday into Monday. Dry weather is expected to return Tuesday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Winter Weather Advisory from 7 PM this evening to 1 PM EST Friday for NCZ033-049-050-501-503-505. Winter Weather Advisory from 7 PM this evening to 10 AM EST Friday for NCZ048-052-053-059-063-064. SC...None.