textproduct: Greenville-Spartanburg

SYNOPSIS

Below normal high temperatures stick around this week. A cold front brings light precipitation today before drier conditions develop briefly Monday. A low pressure system from the Gulf brings better precipitation chances Monday night into Tuesday. Dry high pressure returns Wednesday into Thursday.

NEAR TERM /THROUGH TONIGHT/

As of 904 AM EST Sunday...

Key Messages:

1) Precipitation continues through the morning ahead of an advancing cold front that sweeps across the area this afternoon.

2) Temps still hovering around 32F across some parts of the nrn mountains.

3) Winter Weather Advisory extended until 10 am.

Sfc obs at 14Z indicate several pockets of air around 30-32F from Burnsville to Spruce Pine and along the Escarpment. Think it best to extend the Advisory for another hour to give those locations time to warm up, which should be on track as warm advection continues across the region. Patches of light precip will continue to move across the area ahead of the cold front, so in theory some light icing remains possible.

By late morning, warming temperatures will halt freezing rain, such that an all-rain forecast is warranted everywhere by 10 AM. By this time, a weak z500 shortwave will be located just west of the NC-TN state line, with the attendant cold front located somewhere in the mid/east Tennessee Valley. Following a lull in precip intensity during late morning/early afternoon, scattered light rainfall will push out into the low terrain as the front crosses the region through late this afternoon, with drying taking place from west to east through the day. By late this evening, the entire forecast area should be dry, apart from some isolated NW flow showers...though between limited moisture to begin with, and fairly weak NW winds, there's barely any signal for that in the latest hi-res guidance. CAA behind the front will be weak and short-lived overnight, with a steady but not-so-strong NW wind and temperatures dropping back into the mid-20s at higher elevations and parts of the I-40 corridor, and low- to mid-30s across the Upstate and Piedmont.

SHORT TERM /MONDAY THROUGH TUESDAY/

As of midnight Sunday morning:

Key message: Confidence increasing for accumulating wintry precip in the northern mountains and eastern Escarpment areas, and in very high elevations of the southwest mountains, Monday night into Tuesday morning.

Still expecting dry high pressure to migrate east of the Appalachians Monday and center over the Northeast/Mid-Atlantic coast by late evening. Stalled front to our south will be reactivated as shortwave crosses the Mississippi Valley late Monday, leading to onset of precip from south to north across the area overnight. The longer range CAMs suggest very light precip could begin as soon as 00z Tue in our far southwest mountains and Savannah Valley, with moistening occurring quickly from the top down over the sfc high; precip is likely to have begun over the western two-thirds of the CWA by midnight Tuesday.

Cloud cover moving in Monday afternoon should inhibit nocturnal cooling, but of course precip will induce diabatic cooling and some snow/sleet could be seen at onset where temps are sufficiently close to freezing, which should be most of the mountains. High ridges of the Smokies/Balsams and nearby ranges SW of the French Broad however do look likely to cool below freezing with the diabatic cooling, and with the development of the warm nose aloft via WAA ahead of the approaching system, those areas will transition to freezing rain for a time. However, the valleys and most populated areas in the SW mountains look to remain above freezing overnight and wintry accumulation there is likely to be zero. Rain totals of 1 to 1.5" with isolated spots of 2" or more are forecast for most of the Piedmont with the higher amounts in the usual areas south of the Escarpment near the southern border of NC.

There remains strong consensus for the northern mountains and foothills (NE of the French Broad) to lock in subfreezing temperatures for most or all of the night as in-situ CAD develops. Temps will hover near or just below freezing below the Escarpment such that accumulating ice/sleet/snow may occur in a few areas as far south as NE Henderson County (Bearwallow, Bat Cave, etc.) Raw models do depict many of these areas warming before daybreak and thus the event may prove short-lived, especially those areas farther south. Higher elevations look particularly likely to see sfc temps warm above freezing although profiles would still support snow and perhaps some sleet in addition to rain. We were especially careful with temp trends to try to hone in amounts, with the net result being ice/snow totals that are solidly supportive of a Winter Wx Advisory, although we need to wait a little closer to onset to incorporate more hi-res guidance. WWA decision probably will be made Sunday night, but won't rule out issuance on day shift today.

Temps look likely to have warmed above freezing by 12z Tue, by which time PoPs are forecast to be in decline east of the mountains. Development of CAA Tuesday afternoon should turn precip over to snow on the higher peaks near the TN border, where light accumulation is not out of the question late afternoon into evening. Chances fall below slight-chance by midnight. Several degrees colder Tue night versus the previous night.

LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/

As of 105 AM Sun:

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

Quasi-zonal upper pattern returns briefly Tue night and early Wed with high pressure migrating across the Southeast. The high is comparatively weak to the previous two highs. Winds will be light Wednesday but skies trend clear, and temps rebound slightly. Mid to upper level flow turns slightly cyclonic Wed afternoon; a weak, dry cold front looks to arrive by Thu morning. That should introduce some high altitude cloud cover across the area and upslope clouds and perhaps a few flurries along the TN border at that time. East of the mountains, downslope flow will help bring temps almost back to normal for Thursday afternoon.

Key message 2: Another wintry precip event may unfold for part of the area at some point between Thursday night and Friday night. Confidence remains low.

A 1030mb+ continental high will migrate out of the Midwest and set up over the Eastern Seaboard Thursday night, as the weak front settles near or south of the I-20 corridor. A shortwave will move thru the central CONUS Thursday night into early Friday and induce cyclogenesis along the front--sound familiar? Models remain in disagreement as to when and where the cyclogenesis and frontal activation occurs. The operational GFS develops precip across the TN Valley and Carolinas before daybreak Friday, whereas the 30/00z Euro depicts a deeper and accordingly slower shortwave, delaying onset of precip until Friday afternoon. The GDPS is in the middle but has stayed closer to the Euro. Ensemble members also bear some spread.

Regardless of the timing, it would appear likely in-situ CAD would develop again and portions of the mountains/foothills stand a chance for more wintry weather accumulation. The GFS solution does show mostly snow Friday morning, even outside the mountains; the other solutions depict freezing rain mainly in the mountains--again mainly Friday night. A mixed precip mention did fall out of the forecast process over parts of the area Friday morning, but in light of the forecast range and nearer-term weather impacts, PoPs were kept to slight-chance for most of that activity. A smaller area of higher FZRA chances are forecast Friday night, mainly in the mountains and north of I-40, which appears reasonable. The forecast for Thursday looks more likely to change, although overall it certainly can be said the forecast is low-confidence from Thu night through early Saturday. Friday could prove very cold if precip does develop, with temps not making it past the lower 40s over most of the area, and perhaps remaining below freezing in portions of the mountains.

The GFS actually forecasts yet another system developing in the lower MS Valley on Saturday, and with the Euro also showing continuing precip from the Miller-A, moderate PoPs remain thru the end of the period, albeit with warmer temps Saturday with the CAD potentially eroding.

AVIATION /14Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: MVFR virtually everywhere this morning, with isolated IFR in the Little Tennessee Valley more or less as expected. Scattered rainfall still draped across the NC mountains and parts of the Foothills. Some FZRA is likely occurring in parts of the Blue Ridge...but NO FREEZING RAIN IS EXPECTED TO IMPACT ANY OF THE TAF SITES. Rather, rain will remain all-liquid and hit somewhat of a lull by mid-morning, before shifting eastward and picking up some steam again going into the afternoon. For the Upstate terminals, a few hours of prevailing -RA are carried in the early afternoon, with gradually decreasing confidence on additional rain throughout the day. At KCLT, went with VCSH/PROB30 for the majority of the day. MVFR ceilings are expected to persist for most/all of this period. Gradual drying and improvement is expected by mid- to late-afternoon, with a return to VFR at all terminals Sunday evening. Winds will remain light overnight, picking up out of the WSW during the day, then briefly becoming WNW by late afternoon/evening, more or less concurrent with the end of precip and restrictions. VFR conditions and light NE winds will continue into the first part of the day Monday.

Outlook: VFR conditions should persist through Monday. Another round of rain and associated restrictions is expected Tuesday, before dry and mainly VFR conditions return Wednesday and beyond.

GSP WATCHES/WARNINGS/ADVISORIES

GA...None. NC...Winter Weather Advisory until 10 AM EST this morning for NCZ033-049-050-501-503-505. SC...None.