textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

No changes to the Extreme Cold Warning and Cold Weather Advisory, which remain in place across the area through noon today.

Snow chances have again increased slightly for this weekend, but confidence remains low.

KEY MESSAGES

1. Extreme Cold Warning remains in effect for parts of the mountains, and a Cold Weather Advisory in effect for the remainder of the forecast area through noon today. 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. Very low wind chills will occur across a part of the mountains Tue and Wed nights. 3. Snow chances continue to gradually increase for this weekend in association with likely development of low pressure off the Carolina coast. If snow were to fall, impacts to travel can be expected due to the cold temperatures prior to onset.

DISCUSSION

Key message 1: Extreme Cold Warning remains in effect for parts of the mountains, and a Cold Weather Advisory in effect for the remainder of the forecast area through noon today. 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.

The center of an arctic sfc high continues to settle over the Southeast, with just enough pressure gradient on the northeast side of the high to produce lingering wind atop the forecast area this morning. This is combining with near-record cold temperatures to produce dangerous wind chills across the region. Ambient temperatures are still expected to fall into the single digits across the mountains (with sub-zero readings in the highest elevations), and lower to mid teens elsewhere by daybreak. Temps will then start to rebound with clear skies this morning, but winds will also pick up a tad. So wind chills in the -5 to -20 deg F range in the mountains and 0 to 10 across the Piedmont could linger thru late morning. Thus, the current Extreme Cold Warning and Cold Weather Advisory products noon expiration looks good.

Otherwise, highs should reach the upper 30s to lower 40s for most areas under sunny skies. That said, high elevations could remain below freezing all day. It will remain breezy across most of the area this aftn, and winds actually pick up in the mountains tonight, as a passing reinforcing dry cold front crosses the area. Despite the wind, temps will not be nearly as cold as today; thus, we are not expecting wind chills to quite reach advisory criteria, except for the highest peaks. The day shift can assess whether an impact-based advisory is warranted in the Northern Mountains when the current cold headlines expire, as wind chills may dip into the -5 to +5 degree range late tonight thru Wednesday morning. Lows will be in the teens in the mountains and upper teens to mid 20s in the Piedmont.

Key message 2: Extended cold wave is expected, as temperatures will remain well below normal through the end of the week. Very low wind chills will occur across a part of the mountains Tue and Wed nights.

A long wave trough will remain centered over the East for the foreseeable future, reinforced by periodic short wave troughs. This will result in a continuation of well-below normal temperatures, with max and min temps forecast to be 10-15 degrees below climo Wed through Fri. A short wave passing north of the area is expected to bring another bout of gusty mountain winds and NW/upslope flow light snow showers and flurries Wed night/early Thu. Both wind and snowfall (if any) will most likely be sub-Advisory. The windy conditions combined with temps around 10 degrees below climo could result in Cold Weather Advisory conditions across the northern NC mountains and high elevations. Even in locations that fall short of criteria, the extremely cold temps may have an impact on infrastructure and those vulnerable to the cold due to any pre-existing power outages.

Another arctic high will slide south across the middle of the CONUS late in the week, tightening the pressure gradient across our CWA. Temps should again trend colder by a few degrees Friday night (back to single digits), while winds will increase as well. Hence, Cold Weather Advisory criteria may be met even outside the mountains, as low temps dip into the teens. 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 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: Snow chances continue to gradually increase for this weekend in association with likely development of low pressure off the Carolina coast. If snow were to fall, impacts to travel can be expected due to the cold temperatures prior to onset.

The global models continue to converge toward a consensus regarding the pattern over the East late in the week, as a strong and intensifying speed max is forecast to dig from the Great Plains on Friday to the Gulf Coast on Saturday, sharpening the long wave trough over the East and carving out a deep upper low over the Southeast. The air mass will already be anomalously cold before this evolution, and this pattern will bring even colder conditions...with daily record low max and min temps being in jeopardy for at least Saturday. Just as notably, the strong height falls will almost certainly initiate cyclogenesis near the Southeast Coast over the weekend, with the only question being the usual timing/intensity/location questions that one should expect 5 days out. The 00Z GFS and Canadian models have trended toward a cyclone a little closer to the coast, increasing the potential for frontogenetically-induced precipitation across our forecast area Fri night/Saturday. With cold air already in place...and considering how far south it appears the upper system is going to dig...this would almost certainly be a rare all-snow event for our area, and the potential exists for significant snowfall for at least a part of the CWA. Having said that, confidence remains low...certainly the latest ensemble guidance offers little clarity...and we expect a couple of more days of the model "game on/game off" back and forth that is typical of extended period coastal lows.

Otherwise, temps are forecast to steadily moderate as heights rise early next week. Nevertheless, forecast temperatures are 10-15 degrees below normal during the latter half of the period.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

At KCLT and elsewhere: Very dry conditions with SKC thru the day, then increasing high clouds this evening. So basically a wind forecast, with NW winds still gusty at KAVL, but should become light at all sites by daybreak. Winds toggle to SW at all sites except KAVL, and should see frequent low-end gusts this aftn into early evening. Winds become light again this evening. Then a dry front will cause winds to shift to NW again at KCLT and gusts to resume at KAVL tonight.

Outlook: VFR conditions are expected to continue thru most of the week under a cold and dry air mass. Guidance is beginning to trend toward a possible coastal low bringing a chance of snow to the region Friday night thru Saturday. Confidence remains low, but trends bear watching.

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 01-31

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

RECORDS FOR 02-02

MAX TEMPERATURE MIN TEMPERATURE STATION HIGH LOW HIGH LOW ------- ---------- ---------- ---------- ---------- KAVL 76 1989 16 1908 52 1988 -2 1917 KCLT 80 1989 29 1908 61 1923 10 1917 KGSP 77 1989 28 1951 60 1923 9 1900

GSP WATCHES/WARNINGS/ADVISORIES

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