Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 271349 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 950 AM EDT Tue Sep 27 2016 .SYNOPSIS... A weak wave of low pressure moving just offshore will bring scattered showers and a few thunderstorms 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/... As of 940 AM Tuesday...A weak area of low pressure off the GA/SC coast this morning is expected to move northeast along a coastal trough during the day. The precipitable water will be above 1.8 inches along the coast, while the bulk of the tropical moisture will remain offshore. The HRRR is not that robust regarding rainfall chances and abundant cloud cover will likely hamper significant destabilization. Thus lowered the POPs, but still expect to see scattered showers and a few thunderstorms develop around the forecast area through the evening. Otherwise, the cold front across far western NC will only slowly move east through tonight. Currently favor the cooler MAV numbers, especially across the eastern portion of the forecast area where clouds will inhibit heating the most. && .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 /12Z TUESDAY THROUGH SATURDAY/... As of 12Z...Low pressure off the South Carolina coast combined with a weak frontal boundary to our west will keep convection in the picture through the afternoon hours. Time height indicates quite a bit of mid cloud around today, so we will only get moderately unstable at best. Light northeast winds this morning will become easterly and onshore this afternoon. Light winds tonight with some light fog possible after midnight. EXTENDED OUTLOOK...Scattered SHRA/TSRA Tuesday through Thursday. Cold frontal passage Thursday. VFR expected Friday/Saturday. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 940 AM Tuesday...Weak trough along the coastal waters will result in variable winds across the SC waters and maintain easterly flow across the Cape Fear waters. As low pressure off the GA/SC coast moves northeast during the day expect easterly winds across all waters. The pressure gradient is fairly weak and wind speeds will remain around 10 knots through tonight. Scattered showers and a few thunderstorms are possible through tonight as well. 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. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...JDW NEAR TERM...SRP SHORT TERM...DCH LONG TERM...JDW AVIATION...43 is the U.S. government's official web portal to all federal, state and local government web resources and services.