Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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686 FXUS62 KRAH 090753 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 253 AM EST Sat Dec 9 2017 .SYNOPSIS... A potent upper-level trough will approach from the west tonight, then pass over NC Saturday. A cold front will move east across the region late Saturday. Cold high pressure will follow the front for Sunday into Monday. && .NEAR TERM /THROUGH TONIGHT/... As of 1035 PM Friday... The northward warm nose intrusion into the area earlier this evening brought an abrupt end to accumulating snow across much of the northern Piedmont. The exception is Forsyth County, where the deep near freezing isothermal layer allowed precipitation to fall as all snow. Thus far, snow amounts have averaged 3 to 4" across Forsyth County. East of Forsyth County, the change-over to a rain/snow/sleet mix and in some cases all rain, resulted in lower amounts 1 to 3" across Guilford, Granville and Vance Counties. South of these counties, snow amounts drop off drastically, and were generally a half inch or less, and in most cases trace amounts. For the rest of the night..latest upstream radar and observation data indicate a significant lull in precip has developed western GA, western SC, and western NC. Precipitation is expected to fill back towards daybreak with the approach of the southern stream trough(currently over the Lower MS Valley)moving ENE across the region. Until then, any additional snow accumulations overnight will be very light, with precip falling as a snow-sleet mix and possibly even some brief freezing rain. However, with temperatures only marginally freezing between 31 to 32, any ice accrual should be minor. South and east of the Piedmont, precip will fall as all rain with temperatures holding steady in the mid 30s. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 1045 PM Friday... As the wrap-around precip band moves across the area between 12 to 18z Saturday, cooling aloft will allow precipitation to change back over to snow or a rain-snow mix across the warning and advisory areas. An additional 1 to 2 inches of snow is possible on Saturday as the band moves across the area. This would bring storm total snowfall amounts to 4 to 6 inches across the Northern Piedmont counties, including Vance and Granville counties. As such, the winter storm advisory for those counties has been changed to a winter storm warning to account for the higher amounts. Previous discussion... A wave will swing through the area from the base of the upper level trough, with dry air surging in behind it. Meanwhile, a secondary yet potent shortwave low will be diving southward into the Ohio Valley as the upper level trough pivots over the region. This secondary wave will help finally drive the arctic front through Central NC late Saturday through Saturday night. At the surface, Central NC will remain sandwiched between the coastal front (and the series of lows traversing it) and the arctic front (which will still be hung up over the mountains). Some cooler, drier air will attempt to make its way around the southern fringe of the Appalachians during the day Saturday, helping to push the coastal front further offshore and cut off the moisture feed into the area from the Gulf. The cold air will be chasing the precipitation, which will gradually progress east-northeast out of the area during the day Saturday. Latest model solutions indicate the arctic front won`t make its way through Central NC until Saturday night, after the precipitation moves out. However, the tail end of the precipitation across the northern half of the area could remain snow, or a mix of rain and snow. Do not expect significant additional accumulation of snow beyond 18Z Saturday, although there could be a bit near the VA border. There is a possibility of a few flurries with the passage of the arctic front given the steep lapse rates and lingering low-mid level moisture. However, do not expect any significant impacts with this additional snow activity, should it occur. Confidence is not high that it will. With the rain and clouds sticking around longer on Saturday, highs will be similar to Friday, low to mid 40s. The strong arctic front could bring some blustery winds out of the west-northwest overnight. Strong cold advection behind the front will result in lows in the low to mid 20s Saturday night, though given the expected winds, wind chill values will likely be in the teens across Central NC. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 255 AM Saturday... Fairly low amplitude pattern to begin the long term forecast which will lead to a period of cool but quiet weather to begin the week. This will lead to slightly below normal high temperatures Monday and Tuesday with highs in the middle 40s north and west to mid 50s south and east and lows Monday night in the upper 20s to low 30s. Tuesday night will be a different story however as a clipper system moves through the Great Lakes and a longwave trough digs southward pushing a dry cold front through the area Tuesday night. This will plunge overnight lows into the upper teens to mid 20s across central NC. Strong cold air advection continues on Wednesday during the day as highs will struggle to get out of the low 30s across the northern tier of counties with closer to 40 degrees in the south. This comes in about 15 degrees below normal for mid-December. Only slight moderation for Wednesday night with lows generally in the lower 20s. For the end of the week, there will be a slight warmup during the daytime hours with highs in the low 40s to low 50s north to south but overnight lows will still register below freezing in most locations. The only chance for precipitation comes on Friday as a second clipper system moves across the mid-Atlantic with central NC flirting with the left exit region of a strong upper jet. This could produce some snow showers across the VA border counties, but it is too early to tell if the dynamics will line up just right. In addition, there isn`t a lot of available moisture available so any snow would be of little to no impact. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 105 AM Saturday... 24 Hour TAF Period: Widespread precipitation will affect the region through mid day, before ending from southwest to northeast during the early to mid afternoon. A brief lull in precip across western NC has resulted in ceilings lifting to VFR and MVFR currently, but ceilings will lower between 06 to 12z as precip fills back into the area, with generally IFR/LIFR cigs. MVFR Visibilities will lower to IFR during heavier precip. With regard to P-type, light freezing rain/drizzle at KINT and KGSO will transition to a mixture of sleet and snow, with mostly rain expected elsewhere. KRDU and KRWI could see a brief change over to snow early Saturday afternoon, before ending. VFR conditions are expected to return Saturday night as dry air spreads in wake of the coastal low tracking up the Mid-Atlantic Coast. Outlook: Dry VFR conditions are expected Sunday through mid week. && .RAH WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 4 PM EST Saturday for NCZ007>009-021>024- 038-039. Winter Weather Advisory until 4 PM EST Saturday for NCZ008>010-025- 026-040-041. && $$ SYNOPSIS...BADGETT NEAR TERM...CBL SHORT TERM...CBL/KCP LONG TERM...Ellis AVIATION..CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.