textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

QPF has been decreased slightly through today, mainly due to the slow start to the precip event/difficulty in overcoming dry air near the surface. However, daytime warming/transition to rain has also been delayed across northeast GA and the Upstate, due to the air mass being quite a bit colder than initially expected. Overall, only minor (mostly downward) adjustments have been made to storm total ice.

A Cold Weather Advisory has been issued for tonight for the North Carolina mountains and Rabun County in Georgia.

Temps have trended slightly warmer Monday and Monday night, but still expect dangerous wind chills across the area in the wake of today's ice storm.

KEY MESSAGES

1. A major ice storm is unfolding, with an Ice Storm Warning remaining in effect for the entire CWA. Impacts will be crippling across at least a part of the forecast area, especially where ice accretion approaches or exceeds 0.75". Widespread power outages and extremely difficult to impossible travel conditions are expected to linger through at least the early part of the work week. 2. Gusty northwest winds will combine with falling temperatures to produce dangerous wind chills across the North Carolina mountains and portions of Georgia mountains late tonight through Monday morning. A Cold Weather Advisory has been issued. 3. Gusty northwesterly winds will produce dangerously cold wind chills Monday night into Tuesday morning, which could result in hypothermia or frostbite if precautions are not taken. 4. A reinforcing cold front is expected later in the week with another chance for dangerously cold wind chills Wednesday night and again Thursday night, which could result in hypothermia or frostbite if precautions are not taken.

DISCUSSION

Key message 1: A major ice storm is unfolding, with an Ice Storm Warning remaining in effect for the entire CWA. Impacts will be crippling across at least a part of the forecast area, especially where ice accretion approaches or exceeds 0.75". Widespread power outages and extremely difficult to impossible travel conditions are expected to linger through at least the early part of the work week.

A very cold air mass associated with classical cold air damming has overspread the CWA early this morning, with surface temps ranging from the teens across much of western North Carolina (excluding the valleys west of the Balsams). This air mass is supported by 1040+ mb arctic high pressure currently settling over northern New England. Meanwhile, moisture and insentropic lift associated with activation of the broad baroclinic zone covering much of the southeast quadrant of the Conus is resulting in widespread light precip across the forecast area early this morning. Supplemental soundings provided by the UNCA Atmospheric Sciences Dept as well as ACARS soundings from the Charlotte area reveal a strong warm nose developing as a consequence of intense warm advection above the maturing cold pool. As such, the bulk of precip is falling as freezing rain or freezing drizzle. Although some sleet may mix in at times, especially across far northern areas, freezing rain will remain the predominant...and eventually the only p-type as the warm nose is only forecast to strengthen while the cold layer at the surface will gradually become more shallow. Precip rates will also increase toward daybreak, as isentropic lift intensifies atop the damming region. We may be seeing the beginnings of this with a northeast-moving precip shield that is blossoming over eastern AL/west central GA.

Having said that, there may be somewhat of a lull later this morning...or at least a transition to more of a -FZDZ scenario...esp over eastern areas, as cyclogenesis just off the Carolina coast disrupts the wind and thermal advection fields. Overall, in light of the slow start to the precip event/initial difficulty with overcoming the very dry air near the surface, QPF has trended down a bit with the latest forecast cycle...with total liq equiv forecast amounts mostly in the 0.25-0.5" range now expected through 18Z. Nevertheless, the very cold air mass and relatively modest precip rates should make for very efficient ice accretion...and most areas within the Ice Storm Warning are likely to be in the ballpark of 0.25" of ice by 18Z.

The strong elevated warm advection is still expected to allow most of the valleys west of the Balsams to warm above freezing by late morning, with ice accums generally in the 0.1-0.33" range expected there. Meanwhile, the synoptic pattern supporting cold air damming is forecast to essentially fall apart rather quickly later today, as the parent high shifts into Quebec/becomes detached from the damming ridge, strong wind shear develops near the top of the cold pool east of developing meso-low over the TN Valley, and the cyclone deepens off the coast. Thus, the CAD will certainly begin to erode from the southwest by afternoon. Having said that...the air mass will initially be so cold that it will take some time for even the upper Savannah Valley/SC Lakeland to warm above freezing, and this may not even occur until the cold front/frontal band sweeps through during the afternoon. The relatively high precip rates within the band are therefore expected to fall mostly as FZRA withing the CAD region, and while some of this will be converted to runoff as opposed to pure ice accretion, much of the area will likely a quick additional 0.15-0.3 inch of ice, with storm totals of a solid half inch of ice still likely across much of the area. Locally higher amounts are expected in the upslope region of the southern escarpment, where around an inch is possible. While convection within the frontal band will be elevated, there could still be some gusts as high as 30 kts impinging upon the increasingly shallow cold pool, which could exacerbate the problem of falling trees and limbs. In other words, damage, power outages, and road conditions could deteriorate rather rapidly this afternoon.

Precip will end abruptly by early evening. Any warming above freezing will be brief, as strong cold advection will overspread the area in the wake of the frontal band. Winds will become very gusty from the NW across the mountains overnight, with some scattered snow shower development expected and minor accums possible across the NC counties bordering TN.

Key message 2: Gusty northwest winds will combine with falling temperatures to produce dangerous wind chills across the North Carolina mountains and portions of Georgia mountains late tonight through Monday morning. A Cold Weather Advisory has been issued.

Northwest winds will pick up early Monday morning, with gusts of 40- 60 mph in the high terrain, and breezy conditions elsewhere, as the low pressure system deepens off the East Coast. Wind gusts will generally not quite reach advisory criteria, but with ice-damaged trees and power lines, an impact-based advisory may be needed for at least portions of the mountains Monday. High elevations will see temps cool late tonight thru late Monday morning, and combined with the wind, wind chills dip below -5 F in some spots. Based on expected ongoing impacts from today's ice storm, a Cold Weather Advisory has been issued for the North Carolina mountains and Rabun county in northeast GA from 4 am to 10 am Monday morning. Otherwise, little change in the temperatures with latest forecast, with highs mainly in the teens to upper 20s in the mountains and upper 30s to lower 40s in the Piedmont.

Key message 3: Gusty northwesterly winds will produce dangerously cold wind chills Monday night into Tuesday morning, which could result in hypothermia or frostbite if precautions are not taken.

Temps will be much colder Monday night as continental high centers just west of the region. Temps have trended slightly warmer then previous forecast, but still in the single digits over the mountains and part of the NC Piedmont, and lower teens along/south of I-85. With some wind continuing over the mountains and resultant wind chill, still looks like higher elevations could reach Extreme Cold Warning criteria, with most other mountain areas in Cold Weather Advisory range. With wind chill falling into the single digits over most non-mountain areas, whether we objectively meet criteria will depend on the climatology-based thresholds, but can't rule out impact-based adjustments to criteria given that a very large proportion of the area could be without power. An Extreme Cold Watch may be issued if confidence is high enough for the high elevations of the Northern Mountains.

Not much change in temperature trends for Tuesday and Wednesday. Still expecting temps to plummet well below freezing both nights, and only get into the upper 30s to lower 40s in the aftn across the Piedmont and lower mountain valleys. These cold temps will exacerbate threats of hypothermia for anyone traveling or still without power. Make sure to check up on vulnerable loved ones and neighbors, pets, and have plenty of blankets and warm clothing. Remember to avoid burning fuels like propane or kerosene indoors as this increases fire risk and carbon monoxide poisoning.

Key message 4: A reinforcing cold front is expected later in the week with another chance for dangerously cold wind chills Wednesday night and again Thursday night, which could result in hypothermia or frostbite if precautions are not taken.

Still expecting another shortwave to round an upper low north of the Great Lakes Wednesday and swing thru the Appalachians early Thursday, bringing another cold front. Moisture along the front is minimal, but a brief round of light NW flow snow showers appears possible and is reflected in small PoPs along the TN border Wed night. While temps may remain a bit above freezing in most areas Wednesday, the passage of the front will bring min temps back into the single digits Thu morning near the TN border along with subzero wind chills which could prompt another Cold Wx Advisory or even high elevation Extreme Cold Warning. Mainly teens elsewhere with wind chill above criteria unless an exception is made for power outages as noted previously. Thursday night looks likely to trend a few degrees colder yet again, with wind chills falling into the same categories. High temp Friday could be below freezing in much of the area.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: ***AMD NOT SKED will be carried at KHKY until the further notice due to ASOS outage.*** Light precip...mostly in the form of -FZRA has become widespread across the terminal forecast area early this morning. Predominant flight category at this time is MVFR, but some IFR is beginning to develop across western areas, particularly KGSP/KAVL/KGMU. IFR will eventually settle in at all terminals...probably no later than 09Z or so. Can't rule out some LIFR cigs developing towards sunrise, but this is uncertain, and the potential will be handled with a SCT004. FZRA and IFR/eventual LIFR conditions should persist through much of the daylight hours, although a bit of a lull...or possible development of -FZDZ is possible after sunrise. The lull will be disrupted by a precip band...possibly containing brief +FZRA that will sweep quickly across the area during the late afternoon, with precip ending in most areas by early evening. However, IFR/LIFR restrictions are expected to continue through at least the evening. NE winds of around 10 kts will otherwise continue before weakening later this afternoon/evening. However, brief gusts of 20-30 kts with some westerly component could occur in conjunction with the frontal band this afternoon.

Outlook: Gusty winds will develop early Monday, especially over the mountains and continue through the day. VFR conditions are expected to develop by Monday afternoon and continue through 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

GSP WATCHES/WARNINGS/ADVISORIES

GA...Ice Storm Warning until 1 PM EST Monday for GAZ010-017-018-026- 028-029. Cold Weather Advisory from 4 AM to 10 AM EST Monday for GAZ010. NC...Ice Storm Warning until 1 PM EST Monday for NCZ033-035>037- 048>053-056>059-062>065-068>072-082-501>510. Cold Weather Advisory from 4 AM to 10 AM EST Monday for NCZ033- 048>053-058-059-062>065. SC...Ice Storm Warning until 1 PM EST Monday for SCZ008>014-019- 101>109.