941 FXUS62 KILM 060559 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1259 AM EST Sat Jan 6 2018 .SYNOPSIS... Arctic high pressure over Minnesota, will build into the Carolinas by Sunday. Extreme cold, with very low wind chill values, will continue into the weekend. The frigid airmass will move offshore late Sunday, and temperatures will rebound to normal levels Monday and Tuesday, possibly above normal by Thursday and Friday. A couple of low pressure systems should produce clouds and rain Monday into Tuesday and again Thursday night into Friday. && .NEAR TERM /THROUGH TODAY/... As of 745 PM Friday...Little change to a bitterly cold and fair forecast, with a 'wind chill advisory' posted for early Saturday morning when apparent temperatures dip, as winds elevate at and after Min-T times. GOES-E shortwave ir band showing thin cirrus tracking WSW to ENE across coastal SC presently, so radiational cooling appears poised to release what little absorbed heat was caught today. The GOES-E mid-level water vapor imagery seems to show the sheared short-wave cutting across NC well, that will help deliver increasing low-level north winds early Saturday, as surface high pressure is bolstered. This results in single digit wind chill values in many locations after daybreak, as winds begin punch through the nocturnal inversion. As of 300 PM Friday...Arctic high pressure centered over Minnesota will ooze southeastward into Illinois Saturday, maintaining a very dry and cold airmass across the Carolinas. The passage of a weak mid- level disturbance tonight should result in wind directions becoming more northerly with a modest increase in wind speeds after midnight. Low temperatures are going to be frigid again tonight. Snow cover favors a strong radiational inversion developing this evening which will resist the effect of increasing winds overnight at the top of the boundary layer. However low-level cold advection tends to steepen low-level thermal profiles and erode radiational inversions-- assuming the inversion surface temperature isn't already colder than the air advecting in. I favor the idea that this evening's inversion will resist the increasing winds and that we'll see snow covered areas plummet to 9-14 degrees overnight. I've even got temps as cold as 7 degrees forecast in the Holly Shelter Gamelands east of Burgaw and near Maxton in Robeson County, NC. Conversely, areas with mainly bare ground from Myrtle Beach through Whiteville and Elizabethtown should run several degrees warmer. We'll need a Wind Chill Advisory again Saturday morning for wind chills around 5 degrees at sunrise. 850 mb temps don't budge much from -10C tomorrow, and even with full sunshine we're unlikely to see temperatures rise above the lower to middle 30s. Please see the climate section below for some statistics on how exceptional this arctic outbreak is becoming. && .SHORT TERM /TONIGHT THROUGH SUNDAY NIGHT/... As of 300 PM Friday...Brutal cold persists through this weekend, but there is a light at the end of the tunnel, with Sunday likely the last extremely cold day for the foreseeable future. Arctic high pressure will build SE to become aligned along the Mid- Atlantic coast Saturday night, extending down into the Carolinas. Potentially the coldest 850mb temps of this entire outbreak will flood into the area Saturday night, with 850mb temps dropping to -9 to -12C. This combined with continued snowpack across much of the CWA and light north winds will allow mins to fall towards 10 degrees in the cold sheltered regions, with low to mid teens expected elsewhere. Do not expect ideal radiational cooling with CAA persisting however, so widespread single digit lows are not forecast. The surface high will drift will drift east Sunday into Monday while maintaining a ridge axis back into the Carolinas. At the same time, a shortwave will dive into the middle of the country spawning low pressure development near the Gulf Coast late in the period. While this will do little to the sensible weather locally through the weekend, highs will struggle only into the low 30s Sunday thanks to the very cold start and increasing high level cirrus. Developing WAA Sunday night will allow 850mb temps to climb above 0 for the first time (other than briefly during the storm Wednesday) in a week. This allows for wind decoupling Sunday night so mins will be forecast slightly below guidance as snow pack remains on the ground, and expect one last very cold night with mins dropping to around 20, limited only by the increasing cirrus. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 300 PM Friday...Warmer and wetter weather ahead for next week. High pressure shifts farther off shore on Monday with a deep southerly return flow setting up. This will bring a return of warmer and moister air into the Carolinas. A coastal trough will develop initially with very shallow cold and dense air at the sfc being overrun by this warmer moister air. This could produce some low clouds on Monday but the mid levels will remain dry. The deep trough over the east coast will lift north as a low cuts off over the gulf coast. This system will ride along the Gulf coast as another northern stream system drops a cold front south. The Carolinas will be in between these two systems Mon into Tues with some enhanced lift and possible rain developing on Mon. High pressure will build down behind the weak cold front on Tues into Wed as a ridge builds aloft. The ECMWF and GFS differ through the mid to late week period with the strength of sfc high building down from the north and low pressure system to the south. Therefore not confident in forecast just yet, but looks like there will be a greater amount of clouds and chc of rain through the week. Temps will definitely warm though. Expect temps reaching back toward normal by Mon and above normal for much of the rest of the week. Therefore, no chance of any winter weather through next week. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... As of 06Z...Arctic high pressure has started to spread over the region this morning and will continue to do so today into tonight. region through the overnight hours. Other than some patches of cirrus during the early morning to midday hours skies will remain clear. Northerly winds today may occasionally gust as high as 17 kt in the afternoon, especially near the coast, before becoming light to calm this evening. Extended Outlook...MVFR possible in SHRA Monday, otherwise VFR. && .MARINE... NEAR TERM /THROUGH SATURDAY/... As of 300 PM Friday...Arctic high pressure over the western Great Lakes will move southeastward over the coming days, reaching the Carolinas by Sunday. In the meantime, we're watching the approach of a weak mid-level disturbance that will move across the area shortly after midnight. Northwesterly winds 10-15 kt should shift to the north and increase to 15-20 knots late as the disturbance passes offshore. These winds will gradually diminish during the day Saturday. NOAA and CORMP buoys have consistently reported wave heights a foot higher than model guidance would indicate, so I have increased forecast wave heights through the night by about that much. Winds and wave heights should remain below any advisory criteria. SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... As of 300 PM Friday...High pressure will ridge down from the Great Lakes to become centered across the Mid-Atlantic on Sunday, and then drift slowly offshore Sunday night. As the high centers nearby, a brief period of gusty N/NE winds of 15-20 kts will occur across the waters Saturday night, before slowly veering to the E and easing to 5-10 kts as the gradient relaxes. Seas will briefly rise to 3-4 ft on the gusty winds late Saturday night, but will otherwise be 2-3 ft, falling to just 2 ft late in the period during the weakest wind speeds. LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 300 PM Friday...High pressure moves offshore Monday while a coastal trough develops. Wind should stay light and continue to turn more onshore if not southerly on Monday. Seas will be down less than 3 ft. An area of low pressure to the south and a front dropping down from the north could make for some variable winds through mid week. Overall expect a more SE flow on Mon and more NE flow late Tues into Wed. Winds should pick up and remain on shore through Wed. This should drive the seas up possibly reaching SCA thresholds by late Wed. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Wind Chill Advisory from 5 AM to 9 AM EST this morning for SCZ017-023-024-032-033-039-054>056-058-059. NC...Wind Chill Advisory from 5 AM to 9 AM EST this morning for NCZ087-096-099-105>110. MARINE...None. && $$ NEAR TERM...TRA SHORT TERM...JDW LONG TERM...RGZ AVIATION...III