Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 202330 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 630 PM EST Mon Nov 20 2017 .SYNOPSIS... High pressure will prevail through tonight. A weak trough will develop just off the coast and a cold front will approach from the northwest Tuesday. The front will pass off the coast early Wednesday followed by an area of weak high pressure. Low pressure with origins over the eastern Gulf of Mexico may bring a little rain to the area Wednesday night through Thanksgiving Day. The low will accelerate northeast away from the region by Friday with high pressure expected by the weekend. && .NEAR TERM /THROUGH TUESDAY/... As of 245 PM Monday...Surface high pressure is expected to move off the NC coast this evening and a weak coastal trough will develop. The dry column that has been in place will gradually give way to increasing moisture. Initially, high clouds will begin to spread across the area tonight, then RH will increase in the lower levels during Tuesday. Low temperatures tonight could become problematic as some high clouds possibly limit radiational cooling. At the moment prefer leaning toward the colder guidance with the typical cold spots possibly likely remaining just above freezing (especially northeast zones). The precipitable water will increase more-so during Tuesday as low-level moisture advection increases across the Carolinas. Isentropic lift at 295K along with the coastal front could spark -RA, especially later in the day. Otherwise, favored a blend of MAV/MET/ECE && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 245 PM Monday...Best chance for precipitation during this period appears to be in Tuesday evening time frame, as moisture ahead of a mid-level shortwave lifts out of the Gulf of Mexico and overruns shallow, cool air to the west of a coastal trough. The 12Z NAM/ECMWF are wetter than the GFS, although overall QPF would be on the order of a tenth or two of an inch. By later Tuesday night, a wave of low pressure which is expected to develop along the offshore boundary will move northeast, and this will bring an end to precip chances for the night. The center of surface high pressure will remain to our west through the period, and with mid-level troughiness lingering west of the Appalachians and south into the Gulf, the NAM wants to bring another surge of light, overrunning precip into the forecast area by late Wednesday night. As the NAM is the outlier with this for the moment, will hold off on introducing PoPs for that period for now. Temps slightly above climo Tuesday night, and near climo Wednesday will give way Wednesday night. Cooler air will get pulled southward across the area between surface high pressure to the west, and the surface-H8 low lifting northeast off the Mid-Atlantic coast during that time frame. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 245 PM Monday...The extended forecast will be mostly influenced by an almost standing wave trough across the eastern third of the conus. Ridging will remain focused across the four corners region. There remains some indication of a couple of systems moving across the baroclinic zone to the east but the 12 UTC guidance has jogged eastward. I did trend the forecast in the early periods a little drier so its essentially a dry forecast throughout. Overall temperatures will run a little below normal starting out on the cooler side of climatology with a brief warmup for the weekend. This will be followed by another cold shot early next week. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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As of 00z...VFR conditions and light winds will continue through tonight as high pressure moves overhead, then offshore late. Southerly winds developing above the surface will begin to bring in Atlantic moisture in the form of stratocumulus clouds with bases 3500-4000 feet AGL in the morning between 14-16Z. The is a small chance of mvfr cigs associated with light shra aft 20Z at the coastal terminals but that chance is too small to include in the TAFS attm. Extended Outlook...MVFR conditions may develop in low clouds and light rain Tuesday night through Wednesday morning, then MVFR to IFR conditions are possible late Friday into Saturday in low clouds and rain.
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&& .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 245 PM Monday...High pressure will shift off the NC this evening allowing a weak coastal trough to develop overnight. As a result late tonight into Tuesday morning, easterly wind will back to a light northeast direction on the west side of the trough axis while the flow east of the trough axis becomes southeasterly. The trough will drift closer to the coast Tuesday afternoon with light southeast flow to prevail across the bulk of the waters. Seas are expected to be less than 3 ft through the period and a few showers are possible tomorrow. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 245 PM Monday...A trough along the coast Tuesday evening will make a challenging wind direction forecast. It is expected to be close enough to the coast in the evening to yield ESE winds across the waters, but as a wave of low pressure tracks northeast offshore, winds will shift around to the NW after midnight. Wednesday and Wednesday night, winds will veer from N to NE as surface high pressure extends from the Central Plains states to the Ohio River Valley. The persistent NE fetch between these features will allow seas to build to the brink of Small Craft Advisory thresholds Wednesday afternoon and night in the outer reaches of the marine zones, especially north of Little River Inlet. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 245 PM Monday...Northeast winds of 10-15 knots will prevail through the first two days of the extended marine forecast. There may be a few hours of 15-20 early on but overall 10-15 should do it. By Saturday a modest southwest flow will develop ahead of another cold front which should move across later in the weekend. Significant seas will trend downward from 3-5 feet early to 2-4 and possibly 1-3 feet by Saturday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...SHK NEAR TERM...SRP SHORT TERM...CRM LONG TERM...SHK AVIATION...RAN

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