textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

The Wind Advisory was expanded to include the remainder of the NC mountains, the remainder of the western Piedmont of NC except Union County, the northeast GA mountains, and the Upstate along/N of I-85. All other hazards remain the same.

Updated aviation discussion for 18z TAF set.

KEY MESSAGES

1. Winter Weather Advisory for Madison/Yancey/Mitchell/Avery counties through 12Z Saturday for snow accumulation that will result in some travel impacts. 2. A High Wind Warning remains in effect from 7 PM this evening to 7 PM Saturday evening for portions of the NC mountains near the Blue Ridge Escarpment. The Wind Advisory has been expanded to include all of the remainder of the NC mountains and western Piedmont, as well as extreme northeast Georgia and portions of the northern Upstate, from 7 PM this evening to 7 PM Saturday evening. In general, wind gusts of 45 to 55 mph will be possible in the Advisory area and 55 to 65 mph in the Warning area. These conditions may knock down tree limbs and cause power outages. Stronger winds will increase the likelihood of those impacts but also could be associated with minor structural damage. 3. A Cold Weather Advisory remains in effect for portions of the North Carolina mountains Friday night into early Sunday morning as dangerously cold wind chills could result in hypothermia or frostbite if precautions are not taken. 4. Very low afternoon relative humidity is expected on Saturday along with strong and frequent wind gusts. However, fuel moisture remains high enough due to lingering wet ground from our recent Winter Storms that a Red Flag/Fire Danger statements are not warranted. 5. Significantly warmer conditions continue through the first half of the week. The next round of rain arrives Wednesday into Thursday.

DISCUSSION

Key message 1: Winter Weather Advisory for Madison/Yancey/Mitchell/Avery counties through 12Z Saturday for snow accumulation that will result in some travel impacts.

As expected, radar imagery shows the leading edge of light precip reaching the mtns at 17Z, with cloud top temps well down into the dendritic snow growth zone, so shower activity should be ongoing by the time you read this. Not much change to earlier thinking, other than to be able to see the radar trends which show several bands of precip extending back/NW to central KY. The trend suggests that several hours of elevation-dependent rain/snow showers can be expected for the better part of the afternoon. Mesoanalysis shows sub-33F wet bulb temps across the area from Madison to Avery counties, so a good bit of the precip should fall as snow showers in those zones. Thus, our expected first round of snow shower activity appears to be imminent, or ongoing this afternoon. Once the short wave responsible for organizing this initial band moves past, and the cold front crosses the region early this evening, there may be a brief period of a few hours when the moisture becomes shallow enough to be concerned with ice nucleation. This could result in a brief changeover to freezing drizzle or rime ice over the nrn mountains. Fortunately, the Advisory has already been changed to incorporate all of Madison/Yancey/Mitchell/Avery, so this possible wrinkle is covered. We appear to be on track with the second round of snow showers late tonight/early Saturday, as guidance once again deepens the moisture enough to reach the dendritic growth zone. Snow amounts should be highly variable across those zones, but on average will be below Warning criteria and haven't changed appreciably.

Now that the event is on the horizon, we will also issue a Special Weather Statement for Graham/Swain/Haywood to account for the snow accum over the higher terrain of the Smokies along the TN border. The more populated areas along the US-74 corridor will see very little snow, thus we will not be issuing an Advisory for those zones at this time.

Late tonight and through Saturday morning, the strong wind gusts that develop behind the front may cause some blowing snow that would reduce the visibility at times, so that was added to the forecast.

Key message 2: A High Wind Warning remains in effect from 7 PM this evening to 7 PM Saturday evening for portions of the NC mountains near the Blue Ridge Escarpment. The Wind Advisory has been expanded to include all of the remainder of the NC mountains and western Piedmont, as well as extreme northeast Georgia and portions of the northern Upstate, from 7 PM this evening to 7 PM Saturday evening. In general, wind gusts of 45 to 55 mph will be possible in the Advisory area and 55 to 65 mph in the Warning area. These conditions may knock down tree limbs and cause power outages. Stronger winds will increase the likelihood of those impacts but also could be associated with minor structural damage.

Not much change to earlier thinking with regard to the high wind potential developing tonight and early Saturday across the region. We are still looking at winds increasing across the region as the cold advection sets in behind a cold front this evening. The 850 mb winds still maximize around daybreak Saturday with some pockets greater than 60 kt, particularly along the Blue Ridge Escarpment, and the pressure difference across the mtns still reaches roughly 10 mb Saturday morning, both of which are supportive of very strong wind gusts reaching the ground as the top of the mixed layer pokes up into the higher momentum flow. Overnight and morning guidance from the HREF suggested that Wind Advisory-criteria gusts look to be a really good bet (which is to say...likely) fanning out across the remainder of the western Piedmont of NC (with the exception of Union County NC), the mountains of northeast GA, and the Upstate along/N of I-85 where gap winds can be expected. The Advisory was expanded to include all those areas. In cold advection flows, we often get wind gusts in those areas east of the mtns that end up stronger than what guidance indicates, perhaps not as much as 50-55 mph, but enough to knock down some tree limbs and power lines. The area west of the original High Wind Warning was included in a new Wind Advisory segment to fill in a hole between the Warning and an Advisory issued for east TN, though wind gusts might only reach criteria over the ridgetops. Winds are still expected to diminish during the late part of the afternoon on Saturday.

Key message 3: A Cold Weather Advisory remains in effect for portions of the North Carolina mountains Friday night into early Sunday morning as dangerously cold wind chills could result in hypothermia or frostbite if precautions are not taken.

No changes to earlier thinking with regard to the wind chill situation across the high elevations of the NC mountains tonight through Saturday night. Gusty winds combined with cold temperatures will lead to dangerously cold wind chills of 5 to 15 below zero Friday night into early Sunday morning in Avery County and for elevations above 3,500 feet in Mitchell, Yancey, Madison, Haywood, Swain, and northern Jackson counties. A Cold Weather Advisory remains in effect for these locations from 1 AM Saturday through 7 AM Sunday. Although, wind chills will likely rise above Cold Weather Advisory criteria (greater than 5 below zero) briefly Saturday afternoon, opted to maintain the advisory through daybreak Sunday as wind chills will drop back to criteria around or shortly after sunset Saturday. These dangerously cold wind chills could result in hypothermia or frostbite if precautions are not taken. Use caution while traveling outside. Wear appropriate clothing, a hat, and gloves.

Key message 4: Very low afternoon relative humidity is expected on Saturday along with strong and frequent wind gusts. However, fuel moisture remains high enough due to lingering wet ground from our recent Winter Storms that a Red Flag/Fire Danger statements are not warranted.

Upon extensive coordination with land management agencies, Red Flag/Increased Fire Danger products will not be issued at this time because fuel moisture remains relatively high thanks to our recent winter storms. However, there will be some overlap between very low RH outside the NC mountains, down into the teens Saturday afternoon, and strong wind gusts above 30 mph, such that weather criteria would be met. If fuels dry out more than expected Friday afternoon, the Fire Weather situation will be revisited by the mid shift and statements/warnings might still be issued.

Key message 5: Significantly warmer conditions continue through the first half of the week. The next round of rain arrives Wednesday into Thursday.

By Sunday morning, the Carolinas will be sandwiched between a departing upper speed max over the western Atlantic and a broad split-flow pattern over the Rockies. NW flow aloft will briefly be broken by a weak embedded shortwave crossing the area with little fanfare Sunday afternoon...resulting in little more than increased cloud cover through Sunday evening.

Thereafter, operational guidance depicts a stout increase in sfc theta-e persisting through mid-week as a warmer, moister subtropical air mass settles into the area beneath a broad, low-amplitude z500 ridge aloft. This period should be marked by steadily warming temperatures (with highs in the 50s on Monday, climbing into the 60s by Tuesday and Wednesday) and dry conditions. The muted nature of the ridge may permit some moisture to ride across it, and the general increase in moisture associated with the air mass as a whole means that skies should be partly cloudy at best for most of this period.

By Wednesday afternoon, a compact southern-stream trough originating in the Chihuahuan Desert will arrive in the Carolinas, ushering in additional moisture ahead of a surface cold front. Widespread showers are expected to develop...producing limited QPF response and expected to remain entirely rain at all but the highest peaks of the Blue Ridge. Temperatures should cool significantly behind that front, which will usher back in a cooler polar air mass. A reinforcing cold front arriving sometime Thursday will further entrench cold air across the region once again, bringing temperatures back toward or even slightly below normal. A second round of precipitation associated with this system would appear to have the potential for some snow, mainly at higher elevations in the mountains, but ensemble solutions are all over the place and confidence remains low at this time scale.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

At KCLT and elsewhere: VFR and dry at all terminals outside the mtns. Occasional gusts from the SW can be expected as a front approaches from the west. The front should move through during the evening hours, shifting the wind to W and NW with gusts continuing. A high-based stratocu ceiling might move across the area with the front. The NW wind will be the problem on Saturday, with frequent strong gusts at most terminals through the afternoon hours. The exception will be KAVL, where low clouds should blow up the valley from east TN, bringing a low cloud ceiling this evening. Prevailing VFR is expected, but if any snow showers manage to reach the airport, the ceiling could temporarily drop to MVFR. This will be handled with a PROB30 this evening. Wind will remain gusty NW through the period.

Outlook: Dry, VFR conditions are expected through the rest of the weekend and early next week. Gusty winds continue across the mountains into Saturday evening, but will gradually taper off east of the mountains Saturday afternoon.

GSP WATCHES/WARNINGS/ADVISORIES

GA...Wind Advisory from 7 PM this evening to 7 PM EST Saturday for GAZ010-017. NC...Wind Advisory from 7 PM this evening to 7 PM EST Saturday for NCZ035>037-048-051-052-056>059-062-068>072-502-504-506- 508-510. Winter Weather Advisory until 7 AM EST Saturday for NCZ033- 048>050. High Wind Warning from 7 PM this evening to 7 PM EST Saturday for NCZ033-049-050-053-063>065-501-503-505-507-509. Cold Weather Advisory from 1 AM Saturday to 7 AM EST Sunday for NCZ033-048>052-059. SC...Wind Advisory from 7 PM this evening to 7 PM EST Saturday for SCZ008-101>106-108-109.