Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 271016 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 616 AM EDT Tue Sep 27 2016 .SYNOPSIS... A weak wave of low pressure moving just offshore will bring showers today, mainly along the coast. A cold front approaching from the west will stall through mid-week before moving across the area on Thursday, maintaining warm and unsettled conditions. Cool and dry high pressure will build into the area by the weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 615 AM Tuesday...The story today will be a sfc low that develops just offshore from the SC Coast and is progged to move NE along an inverted sfc trof oriented SW to NE, and just offshore and parallel to the Carolina coasts. The flow aloft in the mid- levels will be increasing from the SW which will help accelerate the coastal low to the NE to off Cape Hatteras by daybreak Wednesday. POPs across the coastal counties will be borderline high chance to likely, then dropping off to low to moderate chance as you push further inland. The pcpn/convection across the far NW portions of the ILM CWA, ie. west of the I-95 corridor, will be from a sfc cold front located over the western portions of the Carolinas this morning. Models indicate this cold front will track off to the east toward the Carolina coasts, but only at a turtle`s or snail`s pace. The other story for the near term period will be the evolution of the closed upper low that will be dropping southward to the southern Great Lakes by Wed daybreak. This will produce the increased SW flow aloft across the FA which accelerates the coastal low to the NE as mentioned earlier. Temperatures will be a consensus of model mos guidance with emphasis on the European guidance.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 400 AM Tuesday...Models are in an o.k. agreement in the closed upper low becoming a cutoff upper low during this period, as it breaks off from the main belt of the westerlies aloft. The cutoff low will drop southward, reaching the Central Appalachians by Friday daybreak. The extremely slow moving cold front from the near term period, will only reach the Carolina coasts toward late Thursday night. Forcing ahead of the cold front will alone keep POPs active Wednesday into Thursday. However, and additionally, dynamics associated with vorts or s/w trofs rotating around the upper cutoff low, like spokes on a bicycle, may combine with the sfc frontal dynamics. And, if this occurs during the max heating of the day, then there will be a possibility that a few strong to severe thunderstorms may occur especially on Wednesday and to a lesser degree during Thursday. The FA does not get directly underneath the cold pool aloft, ie. exhibiting steep lapse rates, associated with the cutoff low. But nevertheless, temps aloft are progged to lower just not to the extreme under the cutoff low itself. Will highlight in the HWO the isolated threat for strong to sever convection. On a side note, SPC does have the ILM CWA within a marginal area on Wed. POPs will generally be hiest in the aftn thru early evening each day. And will carry a low POP during the overnights and early morning hours. Daily MAX/MIN temperatures will run 1 to 2 categories hier than the climo normals thruout this period. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 AM Tuesday...The extended remains a rather lower than average confidence forecast due to discrepancies in the guidance handling an anomalous cut-off low across the OH VLY. The ECM continues to be a slow outlier, but once again the GFS/CMC, which are in very good agreement today, have slowed from previous solutions. This continues to lend some support to the ECM, and a slower progression of the mid-level and surface features is likely, just not quite to the extent the ECM continues to advertise. While this upper low spins and ejects only very slowly NE through the wknd, the surface cold front beneath it will drift east, crossing the local area late Thursday, before being replaced by Canadian high pressure. This suggests that cooler and drier conditions will be in place for the majority of the extended, with temps at or slightly below seasonable norms, and a nice early fall weekend is possible. Must continue to note however that if the ECM ends up correct, this front may not cross until Saturday, leaving much warmer and unsettled conditions in place through the first half of the wknd. && .AVIATION /10Z TUESDAY THROUGH SATURDAY/... As of 06Z...Slow moving cold front well NW of the terminals, and a developing weak low pressure along the coast, will maintain ample cloudiness and possible showers through the valid period. A few showers have developed in the short term forecast period will be marked with a cold front sliding into the forecast area and then stalling. This front will be a focal point for showers and isolated thunderstorms each day. On the synoptic scale a large upper-level low just north of Lake Superior will shift to Ohio Valley by Wednesday night. This feature will be bringing a significant air mass change but this does not begin until after the short term forecast period. The slow moving cold front will be the focus for the heaviest rain on Wednesday into Wedensday night with QPF values running between just over 1". Maximum Temperatures on Tuesday and Wednesday are expected to rise to the middle 80s with the warmer temperatures west of Interstate 95. For lower temperatures values will range from the upper 60s inland to the lower 70s at the coast.long the coast so far this morning, and this is likely to continue through daybreak. Do not expect coverage to be widespread enough for a VCSH mention, so have added a TEMPO group at ILM/CRE/MYR for periodic and brief MVFR. The inland terminals will likely remain dry as the showers along the cold front to the NW are forecast to dissipate as they drop SE. While cloud cover will be significant, much of it will remain the mid-levels, so light fog is possible overnight at LBT/FLO, with winds just above the surface likely too strong for any IFR vsby restrictions. Scattered showers will again be possible during Tuesday aftn/eve, but coverage is expected to be light enough that no mention of any restrictions has been added attm. Best chance for showers during the day will be along the coast, but will handle this potential with later updates. Winds will be generally from the east and less than 10 kts beneath VFR cigs. More stratus will again be possible Tuesday night, especially along the coast. EXTENDED OUTLOOK...Scattered SHRA/TSRA Tuesday through Thursday. Cold frontal passage Thursday. VFR expected fRI/SAT. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 615 AM Tuesday...Winds and seas will be driven by the inverted sfc trof and the weak low moving NE along it. This will result in an easterly flow at the start of this period. Winds will veer to the SE to S this afternoon and evening, and to the SW overnight. The sfc pg will remain somewhat relaxed except as the low passes by. Wind speeds generally 10 to 15 kt, except a more solid 15 kt with possible gusts to 20 kt as the low passes across the ILM NC Waters and temporarily continuing in the wake of this low. The reason for the hier winds and Significant seas will run 2 to 4 ft north of Little River Inlet and 2 to 3 ft south of this Inlet. The ese 1 to 2 foot ground swell at 7 to 8 second periods will dominate the seas spectrum initially. Wind generated waves at 4 to 5 seconds will become dominate during and after the passage of the low. Scattered to areas of convection will affect the waters thruout this period, with the best coverage occurring today into this evening. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 400 AM Tuesday...The area waters will be under the influence of an expansive cutoff low that drops southward to the Central Appalachians by the end of this period. A sfc cold front out ahead of this cutoff low, will continue at a snail`s pace to the east, finally reaching the coastal waters during late Thursday Night. SSW to SW flow will dominate the local waters Wednesday into Thu, then veer to the W and NW depending on the extent the cold front pushes to or partially across the local waters. The sfc pg will slowly tighten-some with time due to the approaching cutoff low. Initially, wind speeds at 5 to 10 kt, then increasing to 10 to 15 kt or around 15 kt, Thu into Thu night prior to the cold front reaching or partially moving across the local waters. Significant seas will hoover, no relation to the vacuum, right around 3 ft. Some fluctuations of 1 foot either higher or lower than the 3 ft will occur. For the most part, wind waves at 4 to 6 second periods will dominate. No underlying 1 to 1.5 foot easterly ground swell at 8 to 9 second periods will be present. Convection may become strong to possibly severe during Wednesday and again on Thu. LONG TERM/FRIDAY THROUGH SATURDAY/... As of 300 AM Tuesday...A cold front will slowly move across the waters on Friday, causing winds to shift from SW at 5-10 kts early, to NW at 5-10 kts late. As high pressure builds down into the area behind this front on Saturday, winds will shift further to the NE, but remain at relatively weak speeds due to the weak pressure gradient. Seas will be 2-3 ft Friday with a southerly 5-6 sec wave being the predominant wave group. By Saturday, wave heights will fall to around 2 ft, possibly building again late in the period as some forerunner swell from a developing tropical system well out in the Atlantic enters the waters.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...JDW NEAR TERM...DCH SHORT TERM...DCH LONG TERM...JDW AVIATION...JDW

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