Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 142323 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 623 PM EST Sun Jan 14 2018 .SYNOPSIS... Chilly high pressure will extend down into the Carolinas from the north through tonight. The high will retreat to our northeast Monday, bringing more seasonable temperatures to our region on Tuesday. A strong upper level trough will cross the region Tuesday night through Wednesday night. && .NEAR TERM /through Monday night/... As of 145 PM Sunday... Quiet, cold, and dry weather will hold through tonight, as the polar surface ridge noses into central NC, although we`ll face bouts of cloudiness as a couple of waves aloft cross the region within cyclonic southwesterly mid level flow. The first perturbation is a weak one, tracking northeastward into W NC, and this in conjunction with an increase in upper divergence associated with upper level acceleration over the Southeast will prompt some high cloudiness over the area tonight. A second, slightly stronger wave will cross the Gulf Coast region late tonight before emerging off the SC coast shortly before daybreak, and this will bring additional cloudiness into our far eastern sections later tonight. But overall, any clouds should be too thin/sparse and high to provide enough downward IR to counter the good radiational cooling conditions posed by the cold air mass and diminishing winds. Lows 12-21. The cool and dry weather will extend through Mon night. The aforementioned wave will track northeastward off the NC coast Mon morning into early afternoon, bringing a few added clouds across our east sections, but otherwise skies will be mostly sunny with just a few altocu. Thicknesses will begin to moderate as the high center pushes further away, and highs are expected to be a bit warmer but still well below normal, 37-45. Lows Mon night 19-24 under fair skies. -GIH && .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/... As of 245 PM Sunday... The initial inland sfc low associated with the high amplitude positive-tilted trough over the NE-central US will fill over the Eastern Great Lakes/NE US late Tuesday-Tuesday night, eventually giving way to a coastal low development well off the Mid-Atlantic Coast Wednesday-Thursday as the potent upper trough assumes a neutral tilt as it pivots east across the region. There continues to be a large model spread WRT to the timing and strength/amplification of the trough and it`s associated ana-frontal precip band, driven by strong shortwave dynamics and f-gen that`s progged to move west-east across central NC late Tuesday night and into the day on Wednesday. Operational versions of the GFS continue to be drier while the Euro maintains up to 0.20" liquid equivalent. With afternoon temps on Tuesday expected to moderate into the 45 to 50 degree range ahead of the attendant sfc cold front, current timing and thermal profiles, still supports precip starting as rain or a rain-snow mix at onset Tuesday night with a west to east change- over to snow early Wednesday morning and into the afternoon(east) as the expansive Arctic High builds in from the west. As previous forecast discussions have noted, one model pitfall and potential forecast concern is that NWP models tend to advect low-level cold air east of the mountains too quickly, which in itself can be a self limiting process as considerable dry sub-cloud layers develop. Given continued high uncertainty, will make only minor changes to current forecast. Current best guess for snowfall amounts are an inch or two from the Triangle north and west into the Triad region, with less than an inch south and east of the Triangle. There may not be any snow accumulation in the sandhills. These amounts are low confidence at this time and will likely change as model guidance continues to evolve. The Arctic blast is very strong with H8 temps progged to crash to -12C to -13C Wednesday night as the parent high settles over the Gulf Coast region. Highs generally in the 30s both Wednesday and Thursday. && .LONG TERM /Friday through Sunday/... As of 200 PM Sunday... Mild surface high pressure over the Southeast early Fri will shift off the coast by the weekend but continue to extend westward into the area, signaling a trend toward mild weather as heights rise aloft. Models are showing widely varying placement and timing of mostly weak southern stream shortwave troughs that cross the Gulf Coast and Southeast during this period, but at this time any such waves will likely hold to our south and/or have too little moisture to work with to result in any adverse weather. A larger, higher- confidence longwave trough moving through the central CONUS late in the weekend should result in increasing clouds in our area by Sun. Expect near normal temps Fri, trending above normal Sat and especially Sun, making for an almost early-springlike weekend. -GIH && .AVIATION /00z MONDAY THROUGH SATURDAY/...
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As of 622 PM Sunday... 24-Hour TAF Period: High confidence VFR conditions will persist through 06Z as high pressure continues to build into the area. There is a chance some low MVFR clouds around in the 1-2 KFT range could develop over KRDU, KFAY, and KRWI between 06Z and 09Z, lingering until 18Z or so. The forecast soundings differ between the NAM and GFS, with the GFS not showing the cloud layer and the NAM showing it. Thus, have somewhat low confidence it will develop, so will keep coverage as scattered, however if it does develop, broken cigs are likely. Otherwise, VFR conditions will persist. Winds will remain relatively light through the period, highest in the east and lowest in the northwest. -KC Looking ahead: High pressure will extend into the region through Mon afternoon before retreating to the NE Mon night, although VFR conditions will persist. Next chance for sub-VFR conditions will arrive late Tue through Wed as a potent upper level trough slowly crosses the region. VFR conditions will return for Thu/Fri as mild high pressure builds in from the west. -GIH
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...Hartfield SHORT TERM...CBL/Franklin LONG TERM...Hartfield AVIATION...KC/Hartfield

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