Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201415 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1015 AM EDT Sat May 20 2017 .SYNOPSIS... Bermuda high pressure offshore will extend inland, helping to maintain fair and very warm conditions. Thunderstorms will begin to increase early next week ahead of a cold front from the west with unsettled conditions persisting for much of the week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1015 AM Saturday...The low-level stratified moisture is on its way in transitioning to heat-spawned cumulus. A line of showers and TSTMS will form into the middle afternoon across central NC along a frontal boundary from roughly Mt Airy to Rocky Mount to the shores of the Albemarle and Pamlico Sounds. The coverage will fill in and expand and begin to drop south reaching Pender county perhaps by 6 PM. This should bring rain into SE NC but diurnal cooling will likely prevent convection from making as far south as Cape Fear. The cold front itself masked by outflows will drop across the SE corner of NC 6z-8z late tonight with isolated showers likely into early Sunday. As of 315 AM Saturday...A narrow mid level ridge will build just west of the forecast area today. This will push a weak boundary from the north to basically bisect the area by early Sunday morning. This boundary may provide just enough impetus to kick off a few showers and thunderstorms across the northern zones late this afternoon and early evening before the loss of daytime heating. We continue to advertise slight to lower chance pops to address this possibility. Afternoon highs are expected to be 3-5 degrees warmer vs. Friday`s values as the close proximity of the ridge warms thermal profiles. Lows for Sunday morning should be in the middle 60s once again as there is little cool air in the wake of the front at least initially.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 315 AM Saturday...This will be a transition period with regard to the longwave pattern aloft. The upper ridging and associated fantastic wx experienced across the FA for much of the past week, will get booted east of the FA by late this period as successive s/w trofs aloft carve out a large amplitude upper trof. Initially, this upper trof will lie across the Central U.S. but then is progged to expand to the East Coast of the U.S. by the end of this period. The upper trof axis will remain positively tilted and generally extending from the Great Lakes to Texas. This position will result in Gulf of Mexico moisture being tapped with low level Atlantic moisture also available. At the start of this period, a stalled frontal boundary will roughly lie across the NC-SC border. Could see widely scattered convection along this boundary due to weak forcing. The atm aloft will start out quite dry early Sun with increasing moisture to occur with PWs increasing to 1.50 to 2.00 inch range Sun night and continuing thru Mon night. The sfc frontal boundary will lift north of the FA by Mon followed by the approach of a cold front from the west during Mon. This front is progged to stall, oriented NE to SW, across the the eastern Carolinas. Forcing ahead of this front along with weak mid- level s/w trofs migrating across the FA, spells an extended period of convection and thus POPs have been adjusted hier to likely to categorical by late Sun night thru Mon night. At the moment, WPC pcpn amounts during this period remain modest at best but will need to monitor future model runs with regard to any increase to pcpn amounts across the FA. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 3 PM Friday...Pattern turns rather unsettled for most of the period, though a few timing and placement issues of the frontal boundary may still need some resolution in future forecasts. A brief respite is possible early Tuesday as deep upper troughiness amplifies over the Great Lakes. This will keep the front active along with its associated moisture, possibly bolstered with Gulf moisture. The speed with which this occurs is not well agreed upon between various models. This moisture may encroach as early as Tuesday but Wednesday is appearing more likely. The upper trough and surface cold front drive through decidedly later Wednesday and wind fields may be strong enough to support a small severe weather threat. Cool and dry air advection appear slated for Thursday and Friday. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... As of 12Z Saturday...LIFR/IFR conditions across all terminals this morning thru 14Z. There-after, expect mainly VFR conditions through midnight tonight followed by possible MVFR/IFR conditions toward daybreak Sun due to the frontal boundary dropping southward and in close proximity. From 12Z to 14Z, the area terminals will experience low ceilings and/or vertical vsby below 1k ft along with horizontal vsby from 1/4 to 1sm in FG and BR respectively. The mid to late May insolation should burnoff and dissipate the fog and low clouds rather quickly. The backdoor cold front will drop southward to the area late today before stalling along the NC-SC border tonight. Ahead of the front, the local terminals will observe another summer`s day with temps in the 80s to around 90 inland. Expect cu development, however it`s vertical development will be retarded due to the subsidence inversion between the 900mb-850mb levels. Thus no convection is expected ahead of this front. Extended Outlook...Reduced flight categories will be possible in widely scattered showers and thunderstorms during Sunday...becoming more numerous late Sunday night thru Wednesday. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Saturday...S wave energy dominating the spectrum in both short period wind-waves, and 7 second `fresh swell` from the same southerly direction. Combined sea height running between 2-3 feet but closer to 2 feet off the inshore SC waters. No significant changes needed to the forecast. A few storms may move over the waters from Surf City to Wrightsville Beach late in the day and could produce outflow winds to 35 KT from the N. As of 315 AM Saturday...A weak southwest flow is currently in place across the waters this morning and this should persist most of the near term period. Speeds are hovering a little less than ten knots and may increase a little with the development of the sea breeze later. The direction may back a little to the south as well. Late tonight a back door front sneaks down and the northern zones will see winds acquire a northerly component. Significant seas will remain limited with the light forcing on the order of around two feet. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 315 AM Saturday...The beginning of this period shows a stalled front extending inland along the NC-SC border. The placement of this front will have a bearing on wind directions across the local waters. Wind speeds initially will be around 10 kt due to a weak sfc pg. The stalled front will lift north of the local waters Monday followed by the approach of the next cold front from the west that models stall across the Eastern Carolinas by the end of this period. Look for winds to become S to SW thruout late Sun night thru Mon night with speeds increasing to around 15 kt. Significant seas thru Sun night will hover around 2 ft. For Mon thru Mon night, seas will build to 2 to 4 ft due to the increasing short period wind driven waves. Not much of any long period swell expected this period, just the 3 to 6 second short period seas. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 3 PM Friday...Placement of the frontal boundary will be crucial to wind directions WITH WIND SPEEDS AT OR BELOW 15 KT EITHER SIDE OF THE FRONT. Flow turns back to the SW by Wednesday with the approach of the next cold front. This second boundary will be stronger at the surface and also accompanied by stronger wind fields aloft. Conditions may worsen to Advisory levels.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...SHK/8 SHORT TERM...DCH LONG TERM...MBB AVIATION...DCH/SGL

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