Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 222004 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 404 PM EDT Sun Apr 22 2018 .SYNOPSIS...
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A slow moving low pressure system will cross the Southeastern U.S. and produce beneficial rains of 2 to 4 inches Monday through Tuesday. Temperatures below normal through Tuesday will bounce back to near normal for the rest of the week. A cold front may drop down into the Carolinas Wednesday night. Another area of low pressure may affect the area on Thursday followed by high pressure on Friday with below normal temperatures heading into the weekend.
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&& .NEAR TERM /THROUGH MONDAY/...
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As of 330 PM Sunday...Surface ridge is maintaining influence across the Carolinas at the moment. Meanwhile areas of low pressure are established across the MS Valley supported by the old upper low across northern Arkansas. As low pressure drifts east the weather will change drastically across the Carolinas during Monday. A strengthening onshore wind will support marginal Wind Advisory criteria along the coastal zones while advecting a lot of moisture into the region. In fact, the precipitable water should approach 1.7 inches during Monday as conditions come together for a widespread heavy rain event. Increasing low-level convergence along with and excellent divergence aloft will create strong upward vertical velocity. As a result of the column saturation and strong lift we anticipate 2-4 inches across the forecast area. While surface based instability is lacking the strong dynamics warrants mentioning isolated embedded thunderstorms as well. While some flood prone/poor drainage areas may receive flooding do not think flood impacts will be widespread enough for a Flood Watch at this time.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/...
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As of 330 PM Sunday...As the area of low pressure across TN/KY fills the low progged to be across GA/SC will become dominant and lift northeast across the Carolinas during Tuesday. As the low moves northeast the strong axis of onshore winds will shift into eastern NC by Tuesday morning. The axis of heaviest rainfall will also shift northward as well during Tuesday with drier mid-level air pushing in from the south and southwest. POPs will trend lower by later in the day with 20-30 POPs lingering for Tuesday night. Followed a blend of MAV/MET number for temperatures. Will need to keep an eye on the high tide Monday night into early Tuesday morning as well - more on the potential for coastal flooding below
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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As of 300 PM Sunday...As one area of low pressure lifts off to the northeast away from the Carolinas on Wed, another one will follow behind it rotating around the main upper trough in a fairly progressive pattern. The winds will veer around on Wed on the back end of the initial low as it pulls away and may see a weak boundary or front drop down into the Carolinas Wed night into early Thurs. The westerly downslope flow on Wed should combine with mixed sun and clouds to produce temps close to 80 on Wed. The second low will track down from the Upper Midwest, becoming an open wave as it digs down into the lower Mississippi Valley by Thurs. The GFS and ECMWF both show this low moving northeast through the Coastal Carolinas Thurs night into Fri, but the GFS is deeper and showing greater QPF and winds overnight Thurs. By Friday, this system will lift off to the northeast with a decent day in store. The GFS and ECMWF differ quite a bit heading into the weekend with the GFS showing a much drier forecast. Either way, a trough will move across the east coast producing below normal temps through much of the late week period.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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As of 18Z...General onshore flow will persist through Monday as low pressure slowly drifts across the mid-Mississippi Valley. Expect VFR conditions through the remainder of the afternoon and into the evening, then ceilings lowering to MVFR late tonight as rainfall overspreads the terminals from SW to NE. Precip should be on the doorstep of KILM by 18Z Mon. Extended outlook...MVFR and possible IFR will persist Monday night into early Tuesday associated with widespread rainfall. Wed through Thursday expect VFR. MVFR possible Thursday night with a cold front, then clearing Friday.
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&& .MARINE...
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NEAR TERM /THROUGH MONDAY/... As of 330 PM Sunday...High pressure centered just east of DELMARVA will maintain an onshore flow across the adjacent coastal waters through tonight. As low pressure meanders along the MS Valley through Monday the pressure gradient between the high and low will allow the onshore fetch to increase with marginal sustained Gales becoming likely. In regards to the Small Craft Advisory we have moved the start time earlier, and upgraded the Gale Watch to a Gale Warning. Seas should have no problem exceeding 10 feet given the size, orientation, and strength of the fetch. Numerous showers expected to develop by Monday, especially across the southern waters initially. Embedded isolated thunderstorms are also possible. SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 330 PM Sunday...Gales will continue at the onset of the short term period with complex areas of low pressure from TN/KY to SC/GA. The axis of strong winds will gradually shift across the waters off eastern NC during Tuesday while the residual seas will remain high through the day. At some point during Tuesday the Gale Warning will need to be lowered in favor of another Small Craft Advisory until seas subside later in the day. By Tuesday night, the SC/GA low will have translated to northeast NC/southeast VA with a much weakened pressure gradient in place overnight. Seas will be highest Tuesday morning, then gradually subside during the afternoon. Seas will continue to subside Tuesday night. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 300 PM Sunday...Winds will diminish as they shift around from on shore to off shore Wed on the back end of low pressure system, as it lifts off to the northeast. A dry cold front may drop into the waters Wed night into Thurs with winds shifting around to a more N-NE direction on Thurs. Fairly low confidence forecast Thurs into Fri as another area of low pressure may affect the waters. As the winds shift around to off shore and lighten on Wed, Seas will subside. Seas should be 3 to 5 ft Wed morning dropping down to 2 to 4 ft by Thurs morning. Winds and seas will be dependent on strength and track of low pressure late Thurs into Fri, but for now have left them in the 3 to 5 ft range, although the WNA shows potential for SCA conditions early Fri.
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&& .CLIMATE...
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AS OF 300 PM Sunday... Meteorological spring began on March 1st, and temperatures since then have averaged significantly below normal. This has been especially true for low temperatures which are running among the coolest values observed up through this point in the year. Here are some statistics on low temperatures since March 1st. Wilmington, NC Coldest Average Daily Low Temps March 1 through April 21 Rank Avg Temp Year 1 41.01915 2 41.61960 3 42.21971 4 42.81962 4 42.82018 <-- 6 43.1 1926 6 43.11981 Wilmington, NC Most Number of March + April Nights with Lows <=40 Rank # of nights Year 1 34 1915 2 26 1960 3 25 1962 4 24 1971 5 23 2018 <-- 5 23 1996 5 23 1983 5 23 1981 5 23 1969 Florence, SC Coldest Average Daily Low Temps March 1 through April 21 Rank Avg Temp Year 1 38.81966 2 40.01960 3 41.81950 4 42.11971 5 42.41962 6 42.61996 7 43.02014 8 43.32013 9 43.52018 <-- 10 43.81984 10 43.81956 12 43.92005 Florence, SC Most Number of March + April Nights with Lows <=40 Rank # of nights Year 1 30 1966 2 28 1950 3 27 1960 4 25 1971 5 24 2013 5 24 1962 7 22 2014 7 22 1996 9 21 2005 9 21 1992 9 21 1983 9 21 1956 13 20 2018 <-- 13 20 1987
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&& .TIDES/COASTAL FLOODING...
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As of 330 PM Sunday...The strengthening onshore fetch may lead to some minor ocean overwash, especially with high tide late Monday night into Tuesday morning. Confidence is higher with minor coastal flooding for the NC coastal waters when the axis of strongest winds are coincident with that particular high tide. If current trends continue then a Coastal Flood Advisory may be needed late Monday night. Minor flooding may also extend into the downtown Wilmington/battleship area with the same tide. Fortunately, regarding astronomical influences the moon is at the first quarter phase.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...Wind Advisory from 10 AM to 8 PM EDT Monday for SCZ054-056. NC...Wind Advisory from 1 PM Monday to 5 AM EDT Tuesday for NCZ106- 108-110. MARINE...Small Craft Advisory from 1 AM to 10 AM EDT Monday for AMZ250- 252-254-256. Gale Warning from 10 AM Monday to noon EDT Tuesday for AMZ250- 252-254-256.
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&& $$ NEAR TERM...SRP SHORT TERM...SRP LONG TERM...RGZ AVIATION...SRP/CRM CLIMATE...TRA TIDES/COASTAL FLOODING...SRP

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