Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 100341 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1041 PM EST Sat Dec 9 2017 .SYNOPSIS...
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Clearing sky conditions this evening will lead to ample sunshine on Sunday, but with continued chilly air as Canadian high pressure builds eastward. A strong cold front will cross the area Tuesday night with Arctic air returning Wednesday. Temperatures gradually moderate Thursday and Friday before another cold front brings cooler temperatures for next weekend.
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&& .NEAR TERM /THROUGH SUNDAY/...
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As of 1000 PM Saturday...Primary vorticity impulse continues to hang back across the western Carolinas but will lift quickly NE tonight to be offshore the Mid-Atlantic by daybreak. A strong vort lobe rotating through the longwave trough has ejected east of the area, noted by much drier air on latest WV imagery overspread the region. This dry air is mostly aloft at this point, and is eroding the local cloud cover, but dewpoints are not falling as quickly as guidance suggests. The true dry advection is behind a weak cold front analyzed across the NC mtns which will race to the SE and across the CWA in the next few hours, and will be noticed by a subtle wind shift from W to NW, along with more rapid dewpoint fall. The slower temp and dewpoint drop has been noted in updated hourly grids. This cold and dry advection will allow temps to drop below freezing well inland, and to freezing at the coast, but with drying and elevated winds persisting all night, think the black ice potential is quite low. Have briefed the oncoming midnight shift about this potential however, and if dewpoints do not drop or winds ease, some patchy black ice will be possible especially inland counties. Sunny and chilly conditions are expected Sunday as Canadian high pressure builds eastward along the Gulf Coast. Highs should only reach the upper 40s, a bit below GFS/NAM guidance but in-line with the ECMWF.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 3 PM Saturday...Local area will remain at the base of a broad mid to upper trough over the eastern CONUS with an almost zonal flow through much of the period. At the surface high pressure to our south will nudge eastward with light SW to W winds through Sun night into Mon. This will allow a slight warming with temps reaching back toward normal after a very cold start Mon morning. The next shortwave will dig south later on Mon into Mon night. This will push a sfc low east with winds backing to the S-SW and increasing slightly allowing for some moisture return late Mon into Mon night. Dewpoint temps will increase from the mid 20s Sun night to the mid 30s Mon night. Sun night will have better radiational cooling conditions with lighter winds and clear skies. Temps will drop down to the mid to upper 20s most places Sun night, and lower 30s along the coast. Temps will attempt to recover on Mon in light S-SW flow and plenty of sunshine, with most highs reaching into the mid 50s. By Mon night the slight increase in SW flow will keep temps about 10 degrees warmer than previous night with mid 30s inland to lower 50s along the coast. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 3 PM Saturday...A series of shortwaves will cross the area during the period, dragging a couple cold fronts with them. The first arrives on Tue. Lack of deep southwest flow ahead of the wave, compliments of the 5h longwave trough, will prevent the wave from generating little more than an increase in cloud cover. Although the front crosses the area during the day temperatures will run near to slightly above climo. The cold air arrives Tue night dropping temperatures well below climo for the middle of the week. Change in 850 temps from Tue to Wed is almost 15C, +3C to -11C. Highs Wed will struggle to reach mid 40s despite full sun should that verify. Next shortwave crosses the area Thu morning, again starved of moisture, and lacks any cold air. Wave exits northeast on Thu as the 5h trough starts to flatten ahead of the next, stronger shortwave. As the 5h trough amplifies to the west, deep southwest flow will develop over the southeast, pushing temps closer to climo. Duration of the return flow is brief and precipitable water values barely reach half an inch. Clouds will increase Thu night as the wave approaches and then passes early Fri morning. Not sold on any measurable precip based on moisture profiles despite the strength of the feature. Cold front trailing the wave quickly crosses the area and shifts offshore early Fri, bringing another round of cold advection to the region late Fri. Advection arrives too late to have a big impact on highs for Fri, but Fri night temperatures will drop below climo. Although this air mass does not look as cold as the one during the middle of the week, temperatures for the end of the period will still be close to 10 degrees below climo. && .AVIATION /04Z SUNDAY THROUGH THURSDAY/...
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As of 00Z...Low pressure has moved away and drier air is rapidly enveloping the area. Cloud cover is quickly eroding from SW to NE, with any IFR/MVFR cigs expected to lift by 05Z at ILM, which will be the last terminal to rise to VFR. Winds may gust for a brief time tonight as a weak front crosses overhead, but will otherwise become NW at around 10 kts. VFR will be the rule Sunday under nearly cloudless sky conditions and winds slowly easing and backing from NW to SW at 5-10 kts. Extended Outlook...VFR through Thursday.
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&& .MARINE...
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NEAR TERM /THROUGH SUNDAY/... As of 1000 PM Saturday...Strong upper level disturbance has pushed off the coast and winds are forecast to increase steadily during the next few hours. This has already begun with JMPN7 gusting to 20 kts last hour, and Frying Pan Shoals reaching nearly 30 kts. Seas will climb as well, although the limited offshore fetch will limit total amplitude. Still expect SCA conditions to develop in the next few hours and persist into early Sunday, and thus the ongoing SCA will remain unchanged, staying in effect until wind speeds drop on Sunday. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 3 PM Saturday...High pressure to the south will move east as next system begins to drop toward the Carolinas by the end of the period. This will maintain lighter SW-W winds Sun night into Mon with winds 10 to 15 kts and seas 2 to 4 ft through Mon. As next area of low pressure pushes a cold front toward the Carolinas late Mon into Tues, the winds will back and gradient will tighten to push winds and seas back up. Expect seas up to 3 to 5 ft by Mon night with SW winds up to 15 to 20 kts. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 3 PM Saturday...Cold front moves across the waters on Tue with offshore flow developing and then increasing as cold advection ramps up. Winds 15 to 20 kt at the start of the period will increase to 20 to 25 kt Tue night into Wed. Offshore component may keep seas within 20 nm of the SC coast under 6 ft but NC nearshore waters seem likely to hit 6 ft and possibly 7 ft at times. Cold advection and gradient slowly weaken on Wed with offshore flow gradually dropping to 20 kt around midday and 15 to 20 kt by the end of the day. Seas will mimic wind speeds, slowly subsiding Wed into Wed night. Flow remains offshore Wed night, before backing to southwest Thu and starting to increase as next cold front approaches from the west. Southerly flow will increase to a solid 20 kt Thu afternoon and evening with seas increasing from around 2 ft Thu morning to 3 to 5 ft Thu evening.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Sunday for AMZ250-252-254- 256. && $$ SYNOPSIS... NEAR TERM...TRA/JDW SHORT TERM...RGZ LONG TERM...III AVIATION...JDW MARINE...

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