Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 240227 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1027 PM EDT Fri Sep 23 2016 .SYNOPSIS... A cold frontal passage followed by modest and dry high pressure will build southward across the Great Lakes and into the Mid- Atlantic region this weekend. Moisture and rain chances will return by Tuesday as the high moves offshore. The next cold front will arrive from the west Wednesday, followed by autumn high pressure accompanied by a dry and cool airmass. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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aS OF 1000 pm Friday...Could see a lingering shower along the immediate coast but for the most part, via latest 88D mosaic trends, the pcpn over land areas looks done. Could see activity fire up over the adjacent Atl waters overnight, but for the most part this activity will be drifting/moving with a southerly trajectory. It could swipe Cape Fear or Cape Romain, but for the most part land areas, away from the immediate coast, should stay pcpn-free. Still a dilemma of whether to go with a predominate stratus or fog night across the ILM CWA. The progged soundings are not clear cut for stratus nor ground based fog. But given dewpoint depressions, although not huge, within the 1k foot agl, will lean toward more fog with indications of areas to widespread. Not very much, if any, tweaking applied to overnight mins. If any, it was towards a degree lower due to the lack of a low stratus blanket across the FA. PREVIOUS.................................................... As of 700 PM Friday...The Flood Watch has been cancelled do to lack of additional pcpn expected. The evening will feature a diminishing and dissipating trend to the showers and isolated thunderstorms as witnessed by the latest mosaic 88D trends and the latest near term models, HRRR RAP and HiResWrf. Will indicate a lowering of POPs over land areas this evening, leaving widely scattered activity over the adjacent Atl local waters. Trajectories in the lower levels tonight indicate the pcpn that develops over the Atl Waters will not have that onshore and inland movement like the past 5 days. May see a few shra develop nearshore and clip possibly Cape Fear or Cape Romain. For the pre-dawn Sat hrs, low level moisture will remain avbl as drier air aloft works its way southward. Will either see low level stratus or ground based fog. Not bought on which wx phenomena will dominate. For now, will include variable amounts of clouds and patchy to areas of fog during the pre-dawn Sat hrs up to a few hrs after daybreak. No tweaks to the min temps needed at this time.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... As of 300 PM Friday...As our low drifts farther south Saturday and high pressure to the north begins to build in, the airmass should dry appreciably from the top down. Precipitable water values in the 1.8 to 2.0 inch range today should fall to 1.5 inches Saturday afternoon and to 1.25 inches Saturday night. Using 850 mb relative humidity as a guide, I am limiting showers Saturday afternoon to just the seabreeze convergence zone of Horry and Georgetown counties in South Carolina, anticipating the airmass will become too dry elsewhere to overcome the convective cap. With skies becoming mostly sunny by late morning, highs should reach the upper 80s inland, 82- 86 closer to the coast. High pressure north of the Great Lakes Saturday will build southward down the Mid-Atlantic coast on Sunday. This should push a cold front through the coastal Carolinas early Sunday. With a building ridge aloft and meager moisture, this front will probably come through dry with only an increase in low-level wind speeds expected. Winds behind the front Sunday should become east-northeasterly, perhaps picking up enough Atlantic moisture for scattered showers to develop and advect onshore. Since this is heavily modified Canadian air that will have spent a thousand miles or so over the warm western Atlantic, low-level lapse rates should be steep which may help support these shallow convective showers. Given the significant post-frontal influence off the Atlantic, I am not forecasting Saturday night and Sunday night low temperatures to fall quite as low as recent MOS guidance would indicate, particularly along the coast. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 300 PM Friday...High pressure will be to our north on Monday but rather than a wedge-like NE flow wind will remain out of the E. This will keep shower chances in the forecast as Atlantic moisture is handily advected ashore. They may tend to favor coastal areas though as mid level ridging keeps the upper levels of the column quite dry. This onshore flow will turn more southerly with the approach of a cold front on Tuesday, its passage slated for Tuesday night. Wednesday and Thursday could feature the strongest cool advection we`ve seen in a while and bring some unseasonably cool weather with Thursday night possibly slipping below 60 away from the coast. A wedge then sets up on Friday continuing the cool weather. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... As of 00Z...Expect a mixture of VFR/MVFR/IFR tonight through Saturday morning due to passing low cigs, isolated showers and developing fog towards morning. Otherwise expect VFR with isolated showers on Saturday. Latest guidance and weather pattern trend continue to suggest potential for widespread fog late overnight into the early morning hours. Thus have noted in going forecast with light winds and passing low cigs. After daybreak, expect conditions to gradually improve to VFR and continue through the remainder of the TAF period. Northeasterly winds will increase to 5 to 8 kts, becoming east- southeasterly in the afternoon hours. EXTENDED OUTLOOK...Chance for SHRA/TEMPO MVFR Sunday. Chance for SHRA/TSRA Tue through Wed. Otherwise expect VFR. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 1015 PM Friday...Rather weak sfc pg and somewhat diffuse pressure pattern to continue across the local waters due to the weak sfc low now well south of the ILM CWA. Will continue with the NE wind directions and speeds at 5 to 10 kt. The pcpn coverage over the local waters has shrunk a good deal this evening but could temporarily peak back up mainly over the offshore waters south of Cape Fear during the pre-dawn Sat hours. With pcpn movements slated to have mainly a southward trajectory, the majority of the pcpn will likely remain over the offshore waters. Significant seas will be totally a function of the 2.0 to 3.5 foot e to ese ground swell at 11 to 12 second periods from Tropical Cyclone Karl. The higher end of this range of swell will occur north of Cape Fear, with 3 to 4 foot significant seas being fcst...and with 2 to 3 foot south of the Cape. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 PM Friday...Surface high pressure north of the Great Lakes on Saturday will build southward down the Mid-Atlantic coast Sunday. This should push a cold front through the coastal Carolinas early Sunday. Winds both ahead and behind the front will be northeasterly, and since the front will come through dry the only change heralding the front`s arrival will be an increase in wind speed. Winds Saturday and Saturday night around 10 knots should increase to around 15 knots for Sunday. These winds, in combination with swells from Tropical Storm (or Hurricane) Karl out near Bermuda, will build seas to 3-4 feet with some 5-footers probably lurking not too far from 20 miles from shore near Cape Fear. LONG TERM /MONDAY THROUGH WEDNESDAY/... As of 300 PM Friday...Monday starts off with easterly winds as high pressure is centered well to our north. This flow will then veer as the day wears on as the high progresses eastward and a cold front approaches from the northwest. This boundary comes through Tuesday night and it will usher in an increasingly strong NE surge of cooler air. Ahead of the front on Monday seas will be quite manageable and any prefrontal increase in seas Tuesday should be quite gradual. This may not hold true with and following FROPA Tuesday night into Wednesday where headlines may become necessary.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...DCH SHORT TERM...TRA LONG TERM...MBB AVIATION...SGL MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.