textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Precip chances have been lowered across southern areas for the rest of the morning.

Updated for 12Z Aviation discussion. Otherwise, no changes since 105 AM.

KEY MESSAGES

1. Temperatures will be below normal through the near term...due mostly to cloud cover today, followed by developing cold air damming tonight. 2. After collaboration with the FFC office, upgraded the Winter Storm Watch to an Ice Storm Warning for our NE GA counties. No upgrade for the rest of the area yet, but we still expect this to be a major winter storm across the entire forecast area, leading to hazardous travel and power outages that may last for days. 3. Dangerously cold wind chills may develop Monday night into Tuesday morning and again Wednesday night into Thursday morning, which could result in hypothermia or frostbite if precautions are not taken.

DISCUSSION

Key message 1: Temperatures will be below normal through the near term...due mostly to cloud cover today, followed by developing cold air damming tonight.

A weak frontal boundary...representing the leading edge of a broad, but steadily intensifying baroclinic zone is located near the I-20 corridor this morning. A band of frontogenesis interacting with an increasingly moist air mass along and south of the boundary is resulting in lingering light showers across ~the southeast quarter of the CWA this morning. These showers will largely move east of the CWA by late morning, and only token small PoPs are warranted in this area.

Meanwhile, a low level ridge associated with sprawling/strong 1050+ mb arctic high pressure over the Great Plains/Canadian Prairie will continue spilling east of the central Appalachians through the period, allowing for gradual establishment/strengthening of cold air damming across our area, especially tonight. High temperatures today will generally be below normal...although northern areas may end up right around climo...as dry air advection associated with deepening NE flow will likely result in some afternoon clearing. Min temps will be below normal in all areas tonight as low level cold advection steadily ramps up in association with developing CAD.

Key message 2: After collaboration with the FFC office, upgraded the Winter Storm Watch to an Ice Storm Warning for our NE GA counties. No upgrade for the rest of the area yet, but we still expect this to be a major winter storm across the entire forecast area, leading to hazardous travel and power outages that may last for days.

The latest guidance still shows a major winter storm will impact our area starting Saturday and continuing thru Sunday night. The ingredients will be in place, with a strong, arctic high moving across the Midwest and Great Lakes, spilling east of the Appalachians and starting a strong cold-air damming set up by early Saturday. Meanwhile, a southern stream trough will advect tropical Pacific moisture across Mexico into the Southeast US and atop the cold air mass. Precip will break out to our west during the day Saturday, and spread in by Saturday evening. By this time, a 1036-1041 mb sfc high will be over Quebec and New England, and a Miller type-B low will develop across the central Gulf states. Profiles will be cold enough for precip to be mostly a mix of snow and sleet at the onset, with models suggesting sleet being the dominant p-type for most of the night Saturday night, but mixing with freezing rain possibly by daybreak Sunday. From there, very strong WAA atop the wedge will strengthen the warm nose, and the sub-freezing boundary layer should shrink, leading to sleet changing over to mostly freezing rain during the day Sunday. For areas outside the wedge, like the Little TN Valley, precip will change over to rain. The latest NBM still wants to bring temps above freezing in NE GA and the western Upstate by late aftn or early evening Sunday, but the higher resolution guidance, like the NAM, is suggesting the CAD will likely not erode that fast. One last band of heavier precip will pass by Sunday evening, as the primary low changes from the TN Valley to a coastal low. There is some uncertainty on how much of the forecast area will still be below freezing when this last bit or precip moves thru. Either way, the latest NBM QPF and p-types produces an uptick in storm total ice for most of the CWFA. We still may see 1-3" of sleet within the heart of the wedge before the ice ramps up. Ice accums of 0.5-.75" seems likely across the I-85 corridor, with 0.75-1.0"+ along the escarpment of the GA/SC mountains and southern NC mountains.

Confidence has increased enough for >0.25" of ice and freezing rain being the predominant type such that the Winter Storm Watch has been upgraded to an Ice Storm warning for our NE GA counties starting at 18z Saturday. For the rest of the area, the bulk of the event is still about 48 hours away at time of this issuance, and there is still some uncertainty on how much sleet will eat into ice totals. So will allow one more forecast cycle before upgrading any more of the watch.

In any case, it still looks like big impacts from sleet and/or ice accums across the entire area Saturday night thru at least Sunday night. Temps may briefly get above freezing Sunday evening as precip tapers off and CAD erodes, but will fall below freezing areawide by daybreak Monday, leading to continued impacts to roads. Winds will become gusty in the mountains and combine with falling temps to produce wind chills below zero in elevations above 3500 ft Monday morning.

In the mean time, continue preparing for a major winter storm. Regardless of the individual p-types, the important thing to note is there will be plenty of wintry precip with this storm. Wintry precip, whether it's ice, sleet, or snow are going to have widespread impacts making for hazardous travel and power outages that could last for days. Prepare an emergency kit for your car/home and replenish fuel for your car and other heating sources such as generators. Remember to keep generator outdoors and at least 20 ft away from entry points to avoid carbon monoxide poisoning. Don't forget about your pets. Keep enough non-perishable food, water, and medications for at least 3 days. Ensure you have warm clothing and blankets as well. Charge your phone and devices in advance so that you are able to receive alerts.

Key message 3: Dangerously cold wind chills may develop Monday night into Tuesday morning and again Wednesday night into Thursday morning, which could result in hypothermia or frostbite if precautions are not taken.

A deep upper trough will swing thru the area in the wake of the winter storm Monday, ushering in a bitterly cold air mass to the region. Temps will remain in the teens to mid 20s across most of the mountains, while briefly getting into the mid to upper 30s in the Piedmont. Then clear skies and light winds will allow temps to plummet Monday night, with just enough NW wind to add a wind chill to already near-record lows for Tuesday, Jan 27. There is some uncertainty on how the NBM members are handling potential snow pack from the winter storm. But nevertheless, lows may dip into the single digits across most of the area Tuesday morning, with wind chills in the Extreme Cold Warning range for the high elevations of the Northern Mountains and Cold Weather Advisory for most of the rest of the forecast area.

The air mass modifies somewhat Tuesday thru Wednesday, but temps remain well below normal. Then a reinforcing cold front will swing thru the area, with a brief shot of NW flow snow Wednesday night. Breezy conditions may produce Cold Weather Advisory criteria wind chills again for portions of the mountains. Temps may stay below freezing across most if not all the mountains Thursday and Friday, while barely getting above freezing in the Piedmont. These temps will make for slow melting of wintry precip accums thru the week and exacerbate threats of hypothermia for anyone traveling or still without power. Make sure to check up on vulnerable loved ones and neighbors, have plenty of blankets and warm clothing to keep warm. Remember to avoid burning fuels like propane or kerosene indoors as this increases fire risk and carbon monoxide poisoning.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

At KCLT and elsewhere: Scattered light showers are forecast to move east of the Terminal Forecast Area by 13Z or so. Prob30s and tempos for -SHRA and associated restrictions have been removed from all TAFs. MVFR cigs have developed at KAND, and these will most likely persist through at least the morning before lifting to VFR by early evening. Otherwise, prevailing VFR conditions are expected through the period, although lowering of cigs to the 035-045 range is likely at the upstate SC terminals and KCLT by late morning. Some clearing/scattering is expected at the NC sites this afternoon as drier air gradually filters through the area, before VFR cigs fill back in overnight. Light/variable or calm winds early in the period will gradually become light NE late this morning, continuing through the day before increasing to 10-12 kts with higher gusts late tonight/early Saturday.

Outlook: A major winter storm is forecast to impact the entire area beginning Saturday afternoon and continuing through Sunday. Significant accumulations of freezing rain/ice and sleet are likely at all TAF sites. Long term prevailing flight restrictions should be expected into Monday when the system finally moves east. VFR is expected to return by Tuesday.

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

GSP WATCHES/WARNINGS/ADVISORIES

GA...Ice Storm Warning from 1 PM Saturday to 1 PM EST Monday for GAZ010-017-018-026-028-029. NC...Winter Storm Watch from Saturday morning through Monday afternoon for NCZ033-035>037-048>053-056>059-062>065- 068>072-082-501>510. SC...Winter Storm Watch from Saturday morning through Monday afternoon for SCZ008>014-019-101>109.