textproduct: Greenville-Spartanburg

SYNOPSIS

Below normal high temperatures stick around through next week. Dry and cold high pressure departs tonight with a cold front bringing precipitation chances Sunday. Drier conditions develop briefly Monday before a low pressure system from the Gulf brings better precipitation chances Monday night and Tuesday. Dry high pressure returns Wednesday into Thursday.

NEAR TERM /THROUGH SUNDAY/

As of 645 PM EST Saturday...

Key Messages:

1) Quiet and cool through late this evening.

2) Wintry mix develops in spots over the mountains late tonight, with isolated light ice accumulations possible.

3) Winter Weather Advisory expanded to include the nrn mountain zones and the area along the Blue Ridge Escarpment north of I-40 in McDowell, Burke, and Caldwell counties beginning 1 AM Sunday.

The storm system responsible for all the wintry weather over the Midwest/Great Lakes this evening will be pushing a cold front toward our region from the west. Precip will stay west of the mtns through at least midnight. Almost always a tricky forecast when precip onset is expected to occur in the pre-dawn hours. There remains a time discrepancy between most of the synoptic scale models and the CAMs, with the CAMs developing precip a few hours earlier along the TN border then expanding/moving eastward through early Sunday morning. In this situation, I'm inclined to follow along more with the timing of the CAMs, so the NBM was blended with the CAMs during the critical hours around dawn. That also goes for the Temps around daybreak. The earlier onset of precip should allow for some evaporative cooling initially, which should allow for pockets of 32F- or-less temps to persist in some locations over the mtns. The effect of these changes to the NBM is to wipe out a model trend that would suggest such a low threat of icing that our Advisory would be overdone. In these situations, we often see a bit more coverage of a light wintry mix than what would otherwise be indicated, so I prefer to err more on the side of caution with a bit greater coverage of light freezing rain potential along the Escarpment north of I-40 where cold air would be trapped the longest into the middle part of Sunday morning. Thus, the Advisory was expanded to include all the nrn mountain zones and adjacent foothill/mtn zones. Timing still looks ok. Warm advection should be able to overwhelm and change all precip to light rain by mid-morning. If we have to extend we can do that early Sunday morning.

The remainder of Sunday looks cloudy with light precip expanding eastward across the remainder of the fcst area. The cold front should start the day far enough to the west that we should get plenty of time on the warm advection side of the boundary, with the front not crossing the region until mid/late afternoon. That should allow temps to actually be a few degrees warmer than today in spite of the clouds and light precip through the morning, though still more than 5 degrees on the cool side of normal. Precip should end from the west with the frontal passage. Not really much of a wind shift behind the front initially, so the upslope precip chances on the TN border behind the front are poor.

SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/

As of 1115 AM EST Saturday:

Key message: Widespread precipitation is expected Monday night into Tuesday. A light wintry mix and ice accumulations remain likely in portions of the mountains and northern NC foothills Monday night into early Tuesday morning.

Atop developing CAD regime, categorical pcpn cvrg will overspread the cwfa Monday night ahead of approaching Miller type A low pressure. Based on the recent speedier model trends it is probable that SW sections of the region will see light pcpn onset before sunset. Otherwise, the sensible wx for Monday will feature thickening clouds as a chilly NE wind caps maximum temperatures around 10 deg F below the December 1st climo. The 29/12z model blend/ensemble pcpn type probabilities continue to favor frza as being the main p-type concern, mainly limited to the northern Blue Ridge. At this point, feel like there is a decent probability that advisory level ice accumulations will occur in NW NC during the pre- dawn hours Tuesday Still expecting rapid dry slot encroachment Tuesday afternoon quickly diminishing pcpn chances, expect for the NC mountains where a period of wrap-around along with caa maintains shower chances into the evening along with Tennessee border snow shower probabilities.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

As of 1215 PM EST Saturday:

Key message 1: Dry weather and moderating temperatures Wednesday and Thursday.

Beneath a quasi-zonal upper pattern, weak sfc ridge axis translates across the cwfa. Sunshine on Wednesday will give way to a little more clouds on Thursday as channeled energy ejects our direction from the southern plains. Moderating temperatures through the period will promote values getting back close to climo on Thursday.

Key message 2: Cool and unsettled weather returns for Friday and Saturday.

Within the broad CONUS l/wv trough, energy is progged to dive SE through the plains on Friday with the associated jet energy aiding to blossom pcpn northward from the gulf coast before ejecting eastward on Saturday. Within this fast moving pattern, considerable uncertainty exists with respect to timing and extent of said pcpn with a large portion of the extended guidance advertising a chilly and mainly light rainy period.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: Seeing mostly BKN to OVC VFR cirrus tracking over the terminals as of 00Z. VFR should linger through the early overnight hours. Conditions will gradually deteriorate during the late overnight hours into Sunday morning ahead of an approaching cold front. Cigs will gradually lower overnight becoming MVFR roughly around daybreak. MVFR cigs should stick around through the early evening hours but cigs may occasionally lift to VFR levels at times. VFR cigs should return for all terminals by 22-23Z. -RA chances will also increase ahead of the front so have PROB30s across the terminals to account for this. -RA may linger past the PROB30 end times but confidence is low. If any vsbys are reduced during the period it will be from -RA. KHKY should see calm to light and VRB winds linger through Sunday morning before toggling more S/SW Sunday afternoon/evening. KAVL will see SE winds linger through the mid- morning hours, toggling more S/SW late Sunday morning into early Sunday afternoon before turning NW by late Sunday afternoon. Winds at KCLT will also start out SE going VRB overnight before picking up out of the SW Sunday afternoon, then NW Sunday evening. Winds across the SC terminals will start out E'ly, toggling more NE overnight into daybreak Sunday before turning SW Sunday afternoon. No gusts are expected across the terminals through the period.

Outlook: Dry and VFR conditions briefly return Sunday night into Monday. Another round of rain and restrictions are expected Tuesday before dry and mainly VFR conditions return Wednesday into Thursday.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Winter Weather Advisory from 1 AM to 9 AM EST Sunday for NCZ033-049-050-501-503-505. SC...None.