Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 090018 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 718 PM EST Fri Dec 8 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 211 PM Friday... Upgrade to Winter Storm Warning for Forsyth... Guilford... Davidson... Randolph... Alamance... Orange... and Person Counties into Saturday afternoon... Winter Weather Advisory for Chatham... Wake... Durham.. Granville... Vance... Franklin... and Warren Counties into Saturday afternoon. Based on satellite, radar, and observational data including heavy wet snow upstream from Jackson to Birmingham to much of western NC (locally already 5-8 inches)... we will upgrade our Northwest Piedmont to a Winter Storm Warning (2-4 inches of wet snow), some locally higher totals possible. The battle of the cold air (very marginal) with surface temperatures just above freezing, and warmer air aloft intruding into mainly eastern NC (or as far west as potentially Greensboro and Lexington this evening), with an initial warm ground have been greatly limiting snowfall accumulations thus far. However, as we lose insolation with nightfall, most guidance suggests snow will continue (very wet) through near sunset, with a potential lull in some areas early to mid evening, before increasing again later tonight. Storm totals of 2-4 slushy inches are possible with locally 5 inches just north of the urban areas of Winston- Salem to Greensboro, and around Roxboro. Roads should be wet to slushy, especially on bridges and overpasses. We will initialize the rain/snow line near the current depiction on radar (which is 25 miles or so SE of model projections) across Randolph/Chatham NE to Warren County, mainly on the NW side of the Triangle area. Snow, some heavy will fall NW of this line, with a transition to rain as the late afternoon and evening progress (warmer air intrusion at 5K feet). Just how far NW this transition goes is in question, but following the average of the guidance and incorporation the wet bulb forecasts, we will place the warning as mentioned. It appears the rain/snow line has stalled, and is most likely going to begin heading back northwest in response to the approaching wave that will continue to enhance precip. rates through the early evening. Lows tonight in the lower 30s in the Warning area, around 32-33 in the Advisory area, and mid 30s to 40 with the rain elsewhere. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 300 PM Friday... 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 /SUNDAY THROUGH FRIDAY/... As of 155 AM Friday... Dry weather is expected for the medium range period, with below normal temps (some days much colder than others). Surface high pressure will build/extend into the area from the Deep South/Gulf Coast States behind the exiting deep trough Sunday. This will result in a brief warm up through Monday and dry weather, with highs on Sunday in the upper 30s NW to the lower to mid 40s SE. Highs Monday are expected to be in the mid to upper 40s, with some lower 50s across the south. The mid/upper level trough across the eastern half of the country is expected to reload by Tuesday, sending another deep/potent mid/upper disturbance and associated generally dry cold front through the area Tuesday. This will result in a renewed push of cold and dry air on Wednesday, with high temps again plummeting into the 30s and 40s. Moderating surface high pressure will build into the area again on Thursday, resulting in moderating temps by Thursday, with highs in the 40s and 50s. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 715 PM Friday... 24 Hour TAF Period: Widespread precipitation will affect the region into Saturday morning, before ending from southwest to northeast mid/late morning into the afternoon. Generally IFR/LIFR cigs are expected, with generally IFR/MVFR visbys (during precip). With regard to P-type, a mixture of sleet and snow is generally expected at KGSO/KINT, with mostly rain expected elsewhere. KRDU could see brief period of sleet mixing in with the rain this evening and tonight though, and all eastern locations may see a brief change over to snow just before the precip ends on Saturday. Outlook: VFR conditions are expected to return on Sunday morning. VFR conditions are then expected into Monday and Tuesday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 4 PM EST Saturday for NCZ007- 021>024-038-039. Winter Weather Advisory until 4 PM EST Saturday for NCZ008>010- 025-026-040-041. && $$ SYNOPSIS...BADGETT NEAR TERM...KCP/BADGETT SHORT TERM...KCP LONG TERM...BSD/ AVIATION..BSD/BADGETT

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