... Wintry precipitation will return across the mountains and over the northern foothills and piedmont of North Carolina tonight as a strong and cold upper disturbance crosses the area. Canadian high pressure will return dry cool conditions Thursday through Saturday, before a moist cold front arrives from the west early Sunday.
NEAR TERM /THROUGH TONIGHT/... As of 640 am EST: No changes to the existing hazard grids are needed on the latest update, although a modest uptick in QPF east of I-77 for later tonight could lead to a slight upward trend in snow amounts there late. For now, a Winter Storm Warning remains in effect across the Tenneseee border counties at elevations above 3500 feet where snow totals tonight should reach 3 to 6 inches despite the fairly short duration of the event. A Winter Weather Advisory for 1 to 3 inches has been issued at lower elevations of the TN border counties. Finally, a shorter duration Winter Weather Advisory has been posted for Davie County for a brief round of possibly intense snow showers crossing the region during the early morning hours Thursday. Details on the setup are below.
Regional radars show a shield of precipitation filling along the stalled frontal zone draped just to the south of the forecast area. Moisture return will continue and increase this morning as a surface wave moves east along the boundary, strengthening the associated baroclinic zone and generating frontogenesis across at least the southeast half of the area. Solid PoPs will result across the region before the wave and the deeper moisture briefly slide east this afternoon. Temperatures will be skewed to the cooler guidance with limited recovery under abundant clouds.
Attention will then turn to the upper wave currently indicated on water vapor imagery over KS/MO this morning. This feature will bring strong DPVA east as it dives into the southern Appalachians by evening. The upper wave will likely induce a surface reflection just east of the mountains that will yield a column of strong forcing across the western Carolinas that translates east overnight. Decent northwesterly flow, with increasing cold air advection, will set up across the mountains through the rest of the morning hours. This will be a fairly short duration event, but signals are there for accumulating snowfall in the aforementioned hazard areas. A "cross- hairs" signature of good vertical velocity intersecting a favorable minus 10 to minus 12 C dendritic growth zone, along with deep moisture, will set up across much of western NC tonight. Given steeper lapse rates out along I-40, wintry pytpes are quite possible, and the forcing, moisture, and cold air appear to align enough for accumulating snow from Davie County NC eastward across the northern NC Piedmont with the passing trough. The western mountains are the most likely candidate for accumulations as snow ramps up along the TN border counties by 00Z this evening with quickly falling snow levels, with the best period of NW flow moisture and cold temperatures in mainly the 03Z to 12Z window. With snow ratios rising steadily overnight, expect a quick 3 to 6 inches at the higher peaks near the TN border, with 1 to 3 inches in the associated valleys. Gusty northwest winds up to 40 or 50 mph are expected as well, along with wind chill values dipping near zero by daybreak Thursday.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 110 AM Wednesday...A strong ulvl jet will persist across the FA to begin the period and push east thru the day. With very good dynamics extending to the lower levels and a 5-6 mb p/grad early on across the NC mtns, winds will remain quite strong and gusty across the higher elevations through at least mid-day. The nw/ly llvl flow will also maintain upslope -snsh where another half inch to an inch will be possible along the TN/NC spine before moisture wanes in the early afternoon.
With a CAA regime in place, expect max temps to be held a couple cats below normal Thu, esp across the mtns and NC fhills/piedmont. Soundings show PWATs dropping to 0.15 inches Thu afternoon as deep layered subs moves in ahead of a stout ulvl ridge. Expect dry BL conds to modify a little moister thru Fri, however, afternoon RH values will drop into the 30 percent range or lower and fire-wx concerns will be possible across NE GA each day. As the new cP airmass settles across the area and llvl CAA continues into early Fri, max temps will again struggle to reach normal levels even within good insol and the sfc flow becoming more s/ly in the afternoon. Mins each night will fall below freezing over all zones, with readings in the low to mid 20s Thu night and only few degrees warmer Fri night.
LONG TERM /SATURDAY THROUGH TUESDAY/... As of 215 AM Wednesday...No major changes were made to the ext range fcst. The latest op model runs still show sigfnt disagreement with the synoptic pattern Sat night thru Mon. The GFS remains a quicker soln than the other guidance and depicts an opening upper trof swinging across the OH Valley. The GFS has been consistent with this scenario the past few runs, however, the slower and a little more srn ECMWF soln has also been d/progging well it/s stronger coastal low setup. These differences will have implications to the sensible weather as the ECMWF would bring a better chance of snowfall and possible -fzra/ip outside the mtns across the NC fthills and piedmont Sun as colder sfc air would have more time to wedge in place.
In any case, will anticipate another round of -snsh mainly confined to the higher mtn elevations and perhaps a -ra/sn mix east with little to no accum. A limiting factor in wintry precip east of the mtns Sun will be the lack of stg mlvl forcing as a slug of h5 vort energy remains generally configed meridonal and doesn/t move in until early Mon when llvl moisture begins a lowering trend. With the continued uncertainty, will keep the fcst -ra/sn and not introduce any p/type issues until or unless the thermal structure becomes more clear. The upper trof looks to become reinforced by diving Canadian energy Mon evening, which would continue forcing to enhance upslope moisture thru Tue. Thus, there could be an extended period of NWFS with the need for continuous snow advisories across the mtn spine thru the latter period. A broad llvl theta/e trof will not modify much during period and will expect temps held below normal a few degrees Sat with a minimal warming trend into early next week.