textproduct: Greenville-Spartanburg

WHAT HAS CHANGED

Updated timing for the end of snowfall overnight, along with new info on additional snow accumulations. Revised temperatures and wind chills through tonight.

No changes to Winter Storm Warning, Extreme Cold Warning, or Wind Advisory with this issuance.

KEY MESSAGES

1. Only light additional snow accumulation is expected overnight. Nonetheless, a Winter Storm Warning remains in effect through 7 AM due to impacts from remaining heavy snow cover. 2. Gusty winds combined with very cold temperatures will lead to dangerously cold wind chills this morning. These wind chills could result in hypothermia or frostbite if precautions are not taken. Similarly cold if not colder temperatures return tonight and Monday morning, though wind chills will not be as severe. 3. Temperatures gradually warm through early next week with dry conditions returning across the region. Precipitation chances return by mid week.

DISCUSSION

Key message 1: Only light additional snow accumulation is expected overnight. Nonetheless, a Winter Storm Warning remains in effect through 7 AM due to impacts from remaining heavy snow cover.

Surface low amplifying off the Outer Banks and still expected to track NE off the East Coast. A broad swath of light radar returns are seen over most of our CWA, with a few narrow bands embedded east of GSP. Think the -SN being reported on automated sensors might actually be blowing snow so hard to know if there is still accumulation ongoing in that area at this hour. Some frontogenetic response is noted above 800 mb on 04z RAP which persists through about 09z near/east of I-77, but moisture diminishes from west to east through then. Accumulating snow is not out of the question but not looking especially likely. Recent spotter reports from 8-10 PM indicated ongoing light snow in the eastern CWA with small accumulations of less than an inch since sunset, that is, substantially lower rates than seen earlier this afternoon. Altogether, maintained chance snow showers in the forecast for the early morning hours but think accums will be an inch at best, and most likely a trace or a couple tenths. Given the expansive light returns and at least weak forcing aloft, kept a flurry mention in all other locations for a few more hours.

Along the TN border, winds are strong and NW'ly. Per soundings taken at UNC Asheville late Sat aftn, and recent RAP prog soundings, the column is becoming too cold for dendritic snow growth, though there remains moisture for some precip production as of this writing. Webcams have the same dilemma as automated obs; can't easily distinguish new snowfall from blowing snow. With moisture expected to diminish overnight and the low potential for the very small crystals to accumulate, think flurries are sufficient as a mention there.

In the lee of the Blue Ridge, where occasional gusts of 35-50 mph are possible thru Sunday morning, blowing snow could cause vsby to drop below 1/4 mile at times. Though the Winter Storm Warning is set to end at 7 AM, hazardous road conditions however will continue through at least Monday morning as temperatures will remain below freezing for most locations. Consider staying put and only travel if absolutely necessary. If you must travel, keep blankets, an extra flashlight, food, and water in your vehicle in case of an emergency.

Key message 2: Gusty winds combined with very cold temperatures will lead to dangerously cold wind chills this morning. These wind chills could result in hypothermia or frostbite if precautions are not taken. Similarly cold if not colder temperatures return tonight and Monday morning, though wind chills will not be as severe.

Tight pressure gradient will be maintained much of the day today (Sunday) even as sfc low departs, with confluent upper flow allowing continental sfc high to expand south across the lower MS Valley. Gusts over higher mountains in the ranges NE of AVL, and along the east-facing Blue Ridge Escarpment, will remain 45-55 mph through late morning. This prompted issuance of a Wind Advisory for that area thru 18z Sunday. Sustained winds of 10 to 20 mph persist even in the valleys. The winds combine with mountain temps dipping into the single digits or even below zero, and widespread wind chills below -15F are expected there through the morning. Outside the mountains, wind is not as strong but with lows in the upper single digits and lower teens, wind chills fall to 0F to -5F in many locations. Extreme Cold Warning in effect for the hazardous cold thru 18z in the mountains/foothills, and 15z elsewhere.

Temperatures today will be tricky as models often struggle to account for snowpack. Favored a blend of guidance which verfied best with last Monday's temps following the weekend ice/sleet; this suggests the mountains remain in the teens and lower 20s thru the day and brings most Piedmont areas to around freezing, comparatively warmer than Saturday's daytime temps in the mid-20s. So, we'll be starting off a little warmer than we were Saturday evening. Winds relax late Sunday as high centers west of the mountains Sunday night. While winds won't be as big of a factor in producing wind chills, the proximity to the high suggests more potential for radiative cooling, and there's the lingering question of snowpack. Considering the various factors, did decide to go a little below NBM for Sunday night mins, most appreciable in the NC Piedmont with 10+ inches of snow on the ground. Otherwise, close to the previous night's lows. Without the wind, Cold Wx Advisory criteria are met but on a more localized basis. Think later cycles of model guidance have a better chance at incorporating the snow cover. Given that and for simplicity of messaging, have not issued any Cold Wx Advisories for Sun night, though won't rule it out once current Extreme Cold Warning expires.

Wind chills could result in hypothermia or frostbite if precautions are not taken. Dress in layers including a hat, face mask, and gloves if you must go outside. To prevent water pipes from freezing; wrap or drain or allow them to drip slowly. Make frequent checks on older family, friends, and neighbors. Ensure portable heaters are used correctly. Do not use generators or grills inside.

Key message 3: Temperatures gradually warm through early next week with dry conditions returning across the region. Precipitation chances return by mid week.

By Monday morning, the upper trof axis will be moving off the Atlantic Coast with a broad area of NW upper flow translating across the Midwest and into the Ohio Valley and Appalachians. Low-level flow will become WLY as the day progresses, helping to bring a gradual end to cold advection as the flow becomes oriented more parallel to the isotherms. Following a very cold start to the day, temperatures are expected to warm at least a number of degrees above freezing across our fcst area, except at the higher mtn elevations. A melt/refreeze cycle will continue, however, with temperatures falling back into the upper teens to low 20s Tuesday morning. Warming continues on Tuesday as a flat shortwave ridge translates over the region with highs expected to reach the low 40s to low 50s.

The next storm system also begins to take shape by this time as broad upper shortwave energy dives down the eastern flank of a tall/stout west coast upper ridge. This carves out a positively tilted upper trof over the Southern Plains by Wednesday with a broad area of SWLY mid/upper flow extending from the Gulf states into the Carolinas. The latest guidance continues to develop a weak sfc low(s) along an advancing frontal boundary Tuesday into Wednesday. A band of precipitation is expected to accompany the front with the leading edge progged to reach the NC mtns late Tuesday afternoon/early evening and then push across our fcst area overnight thru Wed morning. Overall, the synoptic pattern still doesn't look very favorable for significant winter wx with the lack of a well-defined sfc low and a strong positive tilt to the upper trof. Furthermore, it remains unclear how much cold air will be in place ahead of any precipitation. Some ensemble members have a chance for a rain and/or snow mix mainly across portions of the NC mtns and along and north of the I-40 corridor. As such, I have kept a chance for a rain/snow mix across the areas mentioned above, but only elevations above roughly 3500 ft have any snow accumulations. After that, the rest of the week looks mostly dry with temperatures moderating to near-normal.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

At KCLT and elsewhere: -SN likely to continue near KCLT and possibly KHKY thru 08-09z but with little to no additional accum likely. There does remain potential for a heavier snow band to develop and affect either site, prompting TEMPO at KCLT. KAVL may see flurries and/or blowing snow thru daybreak. Otherwise predominantly VFR; all cigs expected to scatter prior to 12z. Gusty NW winds however will continue to be an issue at KAVL into Sunday morning, with frequent gusts upwards of 30 kt. An occasional gust is possible elsewhere thru daybreak but can get by with a brisk sustained wind mention instead. Gusts become more frequent by 14-15z Sun. LLWS likely in the lee of the mountains at KGSP/KGMU through daybreak. Criteria may be met here and there otherwise but confidence too low to mention. Lighter NW to WNW winds Sun aftn onward.

Outlook: Dry and VFR conditions linger Sunday night through at least Tuesday. A cold front may bring precipitation and associated restrictions back on Wednesday.

CLIMATE

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...Winter Storm Warning until 7 AM EST this morning for GAZ010- 017-018-026-028-029. Extreme Cold Warning until 10 AM EST this morning for GAZ010- 017-018-026-028-029. NC...Winter Storm Warning until 7 AM EST this morning for NCZ033- 035>037-048>053-056>059-062>065-068>072-082-501>510. Extreme Cold Warning until 10 AM EST this morning for NCZ035>037-056-057-068>072-082-502-504-506-508-510. Extreme Cold Warning until 1 PM EST this afternoon for NCZ033- 048>053-058-059-062>065-501-503-505-507-509. Wind Advisory until 1 PM EST this afternoon for NCZ033-049-050- 053-065-501-503-505-507-509. SC...Winter Storm Warning until 7 AM EST this morning for SCZ008>014-019-101>109. Extreme Cold Warning until 10 AM EST this morning for SCZ008>014-019-101>109.