textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Light snow showers along the Tennessee border should end by evening.

Winter Weather Advisory is no longer in effect with precipitation having ended and sleet/ice impacts decreasing over much of the area. An Extreme Cold Warning and Cold Weather Advisory remains in place across the area tonight and Tuesday morning.

Chances for precipitation have increased slightly for the upcoming weekend, but confidence remains low.

KEY MESSAGES

1. For tonight, Extreme Cold Warning in effect for parts of the mountains, and a Cold Weather Advisory in effect for the remainder of the forecast area. Wind chills will be dangerously cold in higher elevations, increasing the risk of frostbite. Power outages following the ice storm could increase incidence of hypothermia throughout the area, for individuals without access to heat. 2. Extended cold wave is expected, as temperatures will remain well below normal through the end of the week. Dangerously cold wind chills may return to some areas of the mountains Tuesday through Friday nights. 3. Chance of snow this weekend with potential development of low pressure near the Southeast coast. If snow were to fall, it could easily reintroduce or worsen travel impacts due to the cold temperatures prior to onset.

DISCUSSION

Key message 1: For tonight, Extreme Cold Warning in effect for parts of the mountains, and a Cold Weather Advisory in effect for the remainder of the forecast area. Wind chills will be dangerously cold in higher elevations, increasing the risk of frostbite. Power outages following the ice storm could increase incidence of hypothermia throughout the area, for individuals without access to heat.

NW flow snow showers should diminish by late afternoon or early evening over the mountains. Only light additional accums are expected for most locations, a little more for the highest elevations.

Temperatures will fall into the lower teens and single digits tonight, with some high elevation locations near zero. With windy conditions remaining across the mountains, wind chills are forecast to fall to -15 or lower across Avery County, above 3500 feet across the remainder of the Tennessee border counties and northern Jackson County. The Extreme Cold Warning remains in place for these areas for tonight and Tuesday morning. The rest of the CWA remains in a Cold Weather Advisory even though winds drop off outside of the mountains and in sheltered mountain valleys. This could keep some locations from reaching criteria, but with power outages continuing, it's prudent to keep an impact-minded Advisory for all areas outside the Warning.

The windy conditions continue across the mountains into Tuesday, but gusts should remain below advisory levels for all but the highest elevations. Gusty winds diminish this evening outside of the mountains but pick back up on Tuesday.

With full sun, highs should reach the upper 30s to lower 40s for most on Tuesday. That said, high elevations could remain below freezing.

Key message 2: Extended cold wave is expected, as temperatures will remain well below normal through the end of the week. Dangerously cold wind chills may return to some areas of the mountains Tuesday through Friday nights.

We will be stuck in a cold weather pattern thru the week, with a portion of the polar vortex extending into eastern Canada and the northeastern CONUS. A series of vort lobes will swing around the vortex and supply reinforcing shots of very cold air southeastward across our region. That said, temperatures have trended up slightly with this forecast cycle, possibly as models incorporate less snow/sleet/ice accumulation than on earlier runs, but forecast min/max values still remain 10 or more degrees below normal through next weekend.

Tuesday night and Wednesday morning, northwest flow continues across the mountains. Moisture is marginal, but a few flurries or light rime icing could occur along the TN border. CAA will remain strong at that time and gusts of 35-45 mph could occur on ridgetops. Though temps won't be as cold as Monday night, a few high elevation spots will see wind chill dip below -5F on account of the wind. A shortwave will cross the area Wednesday, helping to maintain similar NW winds and wind chills at that time. Model/ensemble QPF response has diminished for Wed night and PoP is no longer sufficient to include a slight-chance snow mention in the NW Flow areas, but again flurries would be no surprise. Both Tue and Wed nights, the high elevation wind chills appear marginal for Cold Weather Advisory based on objective criteria, but even so, the extremely cold temps may have an impact on infrastructure and those vulnerable to the cold due to any pre-existing power outages.

Forecast temps are similar Thursday night, but with lighter winds the extent of subzero wind chills is smaller, though impact still could be higher than usual. Another shortwave/strong vort lobe will pivot around the polar vortex and drop south thru the Midwest and Ohio Valley Friday. This will allow another arctic high to slide south across the middle of the CONUS, tightening the pressure gradient across the CWFA. Temps should again trend colder by a few degrees Friday night (back to single digits), and winds tick upward as well. Hence, Cold Weather Advisory criteria may be met even outside the mountains in spots, as low temps dip into the teens there and Advisory threshold is warmer. Based on two-day average temperatures, all three of our climate sites (AVL, GSP, CLT) look to be well within Cold Wave criteria heading into the next weekend, so a Special Weather Statement may be issued to address concerns about longer-duration cold leading to greater impacts such as greater incidence of frozen pipes.

Key message 3: Chance of snow this weekend with potential development of low pressure near the Southeast coast. If snow were to fall, it could easily reintroduce or worsen travel impacts due to the cold temperatures prior to onset.

26/12z GFS and GDPS are reasonably similar to the 26/00z ECMWF in showing the Midwest shortwave cutting off into an upper low near the southern Appalachians, inducing strong height falls Saturday as far south as the Florida Panhandle. There remain some differences in timing and depth of the low, but there is consensus for the upper low to induce cyclogenesis near the GA/SC coast Saturday or early Sunday. The number of global ensemble members depicting this evolution have increased since this time yesterday. Some GEFS members still develop light snow downstream of the mountains in NC/VA as a result of the shortwave itself, so that can't be written off either, just yet, and if nothing else light NW Flow snow could result in the usual area. Nevertheless, sfc temps are forecast to be below freezing over almost all the area Saturday owing to the freshly arrived Arctic airmass. LREF member sounding wet-bulb profiles are virtually all below freezing thru the column, and fwiw, pattern recognition and partial thickness nomogram technique suggest p-type would be all snow as well. It appears to be mainly whether the developing precip shield extends far enough NW to include our CWA. This probability has increased and so PoPs are now in the 30% range for a portion of the Piedmont. The situation continues to bear watching, given that the prolonged cold temps ahead of this system would make even light snow stick to roads more than usual, and lead to slippery conditions. Precip chances currently peak over the Piedmont Saturday but NW Flow snow could continue into Sunday.

AVIATION /18Z MONDAY THROUGH SATURDAY/

At KCLT and elsewhere: ***AMD NOT SKED will be carried at KHKY until further notice due to ASOS outage.*** MVFR stratocu, and isolated light snow showers, continue across the mountains, occasionally affecting KAVL. Have a TEMPO for KAVL for this afternoon. MVFR or low VFR stratocu is also being seen in convergence zones downstream of the mountains. These are generally staying away from the TAF sites but would create cigs if they shift and move overhead. Don't have any restrictions as this time since they have not been directly overhead. Gusty N to NW wind, W at KAND, will continue through the afternoon and diminish into the evening, but lingering at KAVL. Winds turn SW for all but KAVL Tuesday morning. Low end gusts are expected but may hold off until after this TAF period. KAVL will keep a NNW wind and may see low end gusts on Tuesday as well. SKC expected once the stratocu dissipates later this evening.

Outlook: VFR conditions are expected to continue thru much of the week under a cold and dry air mass.

CLIMATE

RECORDS FOR 01-27

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 80 1999 17 1940 54 1916 2 1986 KCLT 75 1890 24 1940 58 1890 6 1940 KGSP 73 1954 29 1940 57 1949 8 1940

RECORDS FOR 01-28

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 75 1914 7 1897 52 1916 -2 1986 1897 KCLT 79 1944 20 1897 59 1916 5 1986 KGSP 77 1944 29 1986 55 1957 5 1986

RECORDS FOR 01-29

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 76 2002 25 1977 52 1917 -1 1897 1897 KCLT 79 2002 29 2014 59 1957 8 1897 KGSP 78 2002 27 1897 57 1957 6 1897 1916

RECORDS FOR 01-30

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 76 2002 11 1966 55 1950 -7 1966 1914 KCLT 78 2002 19 1966 59 1914 4 1966 KGSP 76 1975 20 1966 53 2002 -6 1966

RECORDS FOR 01-31

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 78 1975 13 1909 57 1950 1 1966 KCLT 77 1975 27 1909 59 1950 4 1966 KGSP 79 1975 31 1934 60 1950 3 1966 1909

RECORDS FOR 02-01

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 74 1950 22 1898 55 1950 4 1909 KCLT 76 1950 27 1900 55 1896 10 1900 KGSP 73 1957 30 1980 56 1969 9 1900 1936 1950 1916

GSP WATCHES/WARNINGS/ADVISORIES

GA...Cold Weather Advisory from 6 PM this evening to noon EST Tuesday for GAZ010-017-018-026-028-029. NC...Cold Weather Advisory from 6 PM this evening to noon EST Tuesday for NCZ035>037-048>053-056>059-062>065-068>072- 082-501>510. Extreme Cold Warning from 6 PM this evening to noon EST Tuesday for NCZ033-048>052-059. SC...Cold Weather Advisory from 6 PM this evening to noon EST Tuesday for SCZ008>014-019-101>109.