Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201334 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 934 AM EDT Fri Apr 20 2018 .SYNOPSIS...
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Canadian high pressure will build into the Carolinas through the weekend, bringing dry weather with chilly temperatures. Slow- moving low pressure will cross the Southeastern U.S. Monday through Wednesday, bringing widespread rainfall with continued below-normal temperatures.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 930 AM Friday...Deep dry northwest flow aloft veers northeasterly at the surface as 1035 mb high pressure over Minnesota slowly builds eastward. The 12Z MHX weather balloon measured 0 degrees C at 850 mb this morning. Interestingly, matching today`s date up on the SPC sounding climatology page shows that while this is unusually chilly this late in the year it`s not really record territory. Surface winds should continue to veer through the day, and by this afternoon a weak seabreeze should turn winds purely onshore, perhaps even along the Brunswick County beaches. For this reason predicted highs range from only 59-63 degrees on the beaches to the upper 60s across the Pee Dee region. This is 10-12 degrees colder than normal. Through yesterday April has run 1-2 degrees colder than normal and today`s temperatures should extend those negative departures by another half degree or so. Good radiational cooling tonight will be partially offset by warm advection. Lows should range from 38-44, except a few degrees warmer on the beaches. It`s possible there could even be some patchy frost in some of the normally colder locations across SE North Carolina. I`ll investigate this potential more closely after the 12Z model data arrives.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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As of 330 AM Friday...The forecast area will lie between 2 "bowling balls", ie. between 2 upper closed lows at the start of this period. The 1 affecting Maine and southeast Canada, will progress further away from the U.S. during this period. However, the other closed low will be able to progress, moving slowly eastward across the Gulf Coast States this weekend, and reaching the ILM doorsteps by Mon morning. At the sfc, models in decent agreement with Canadian High pressure ridging across the area from the Great Lakes during this weekend, with the high re-centering itself over the NE States at the end of this period. This will result in cool NE to ENE winds thruout this period which will help keep temperatures at 5 to 10 degrees below normal for both maxes and mins with the exception of Sunday night/Monday morning lows which will be near normal due to the modification of the air mass as well as onshore winds that may have a SE component by the end of this period. Clouds Sat through Sun will be in the form of thin Cirrus Sat and becoming more opaque during the day on Sun. For late Sun through Sun night, mid-level altostratus will become dominant with low level stratus across the far S to SW portions as the upper low approaches along with the threat for stratiform rains.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...Very large high, more typical of the cool season, to be moving off the coast on Sunday. Meanwhile a cutoff upper low (also normally a cool season feature) to be crossing the Gulf States, leading to cyclogenesis. As often the case with a cutoff, the timing is often uncertain and too fast in guidance. Much of the cloudiness and rain expected to overspread the area Sunday night into Monday may now be about 12 hours slower. Another change from this time yesterday is that guidance is now suppressing the highest rainfall amounts to our south. Given the strength of the high to our north this seems plausible. Even so, the system will be slow moving and keep rain in the forecast through at least Wednesday. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 12Z...VFR conditions are expected through the period. High pressure centered to our northwest will build in through this evening. Northerly winds may bump up after sunrise, but should stay under 15 kts for the most part. Light winds tonight with good radiational cooling conditions. Extended outlook...VFR. Periods of MVFR/RA Monday/Tuesday.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 930 AM Friday...The Small Craft Advisory has been extended through noon due to continued breezy northeast winds still blowing 20-25 kt across the coastal waters. Winds at 8 AM were still gusting to 33 knots out at the Frying Pan Shoals buoy. Wind speeds should diminish through the day, and will veer more directly onshore during the mid to late afternoon hours as a weak seabreeze develops. Seas still 7.5 feet at Frying Pan are probably not being experienced within 20 miles of shore. The CORMP buoys near Cape Fear are reporting 4 to 4.5 feet, and these seas should diminish through the afternoon as wind speeds diminish. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 330 AM Friday...The area waters will remain within a semi-tightened sfc pg Sat that will likely further tighten Sun into Sun night. This due to the closed low approaching from the Gulf Coast States. Have ramped up ENE to E winds late Sun through Sun night and have them approaching SCA thresholds by Mon daybreak along with building seas likely breaching the 6 foot plateau Mon morning. Significant seas will primarily be a function of wind driven waves that could be considered a pseudo ground swell as progged periods increase to 5 to 7 seconds. LONG TERM /SUNDAY THROUGH TUESDAY/... As of 300 PM Thursday...Onshore flow on Sunday the result of a very large area of high pressure moving eastward but remaining centered well north of the area. At the same time low pressure will be developing over the Gulf States. This setup will increasingly squeeze the gradient to where wind and seas both reach advisory levels. Both entities will be very slow moving, keeping advisory flags flying for the remainder of the period.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Small Craft Advisory until noon EDT today for AMZ250-252-254- 256.
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&& $$ SYNOPSIS...TRA NEAR TERM...TRA SHORT TERM...DCH LONG TERM...III AVIATION...DL

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