Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 140038 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 738 PM EST Sat Jan 13 2018 .SYNOPSIS... Cold and dry high pressure will slowly wedge down the east coast through Monday. An area of low pressure will develop off the Carolina coast and may bring a period of wintry precipitation Tuesday night into Wednesday evening. Arctic air will reach the Carolinas Wednesday and Thursday and may bring dangerously cold wind chills. Temperatures will begin to moderate Friday and should surge above normal levels next weekend. && .NEAR TERM /THROUGH SUNDAY/...
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As of 738 PM Saturday...Recent scans of the GOES-E Night Fog channel, shows drying NNW-N wind is rapidly eroding portions of the cloud deck hovering around the Cape Fear region early this evening. There may still be opportunity for a few clouds to form near the moist base of a lowering inversion overnight, but overall, drying trends should win-out, into a fair overnight period, and chilly, below average, below freezing. Surface dewpoints will trend notably lower into early Sunday, teens to around 20, making for exceptionally low indoor RH. Forecast in good shape, mainly tweaked sky cover grids, no big changes. As of 300 PM Saturday...Cold advection which began earlier will continue this evening and overnight as Arctic high builds in from the northwest. Vary amounts of stratus across the area this afternoon will dissipate by early evening and skies overnight should be mostly clear. Combination of pinched gradient and cold advection will keep boundary layer winds elevated overnight with the strongest winds closer to the coast. Partial thickness values suggest widespread lows in the lower 20s which would be pretty impressive given boundary layer winds should curtail radiational cooling. Although the cold advection shuts off for tomorrow the in situ airmass combined with north to northeast winds around 15 mph will work to keep highs at or just below 40 despite an abundance of sunshine. Precipitable water values drop into the low teens tomorrow with single digit dewpoints highly likely and RH will dip into the low to mid 20% range.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... As of 300 PM Saturday...As of 300 PM Saturday...Cold and dry high pressure extending down through the Southeast from New England begins to get squeezed out as next mid to upper trough digs down and pushes cold front toward the Carolinas early Tues. A coastal trough also begins to develop by the end of the period. Bitter cold temps are expected overnight Sun and to start the day on Monday. The winds will lighten which will make for more bearable wind chills early Mon, but will also help to produce better radiational cooling. A fairly potent shortwave will ride around the base of the mid to upper trough which will squeeze out the very limited moisture we have through the column to produce some passing clouds after midnight Sun night to around daybreak Mon. There may also be a spike in winds around daybreak. This may affect the temps up a bit. The GFS is a bit more bullish with clouds and therefore has temps a few degrees warmer. Overall expect temps within a few degrees of 20 for lows Sun night. Any winds will make it feel like the lower teens in many spots to start the day on Monday. Any clouds will dissipate Mon morning and temps will recover into the mid 40s with plenty of sunshine and very light northerly to variable winds at the surface. Low level winds will shift around to the W to SW late Mon into early Tues ahead of next system. This will help 850 temps rebound about 4C rising from below 0c to a couple of degrees above 0c. With that being said, the atmosphere will decouple Mon night with calm winds and clear skies, and the WAA will most likely not be felt until mixing occurs Tues morning. Therefore, temps should drop hard down between 20 and 25 most places with some colder readings in traditionally cooler spots. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM Saturday...Arctic air will briefly surge back across the area during the middle of next week and may bring some wintry precipitation and a brief period of dangerously cold wind chills. A deep longwave trough will dig across the eastern third of the nation Tue and Wed and then lift off to the NE and way from the Carolinas Wed night and Thu. The next disturbance will move out of the Four Corners region Wed, the Southern Plains Thu and the Gulf Coast states Fri, perhaps reaching the Southeast states Sat. At the surface, the wedge of high pressure is expected to break down on Tue. The forecast then becomes more unclear and the latest Euro is not consistent with its previous run in showing low pressure developing just off the Southeast Coast. Instead it now offers a solution a little closer to the GFS with weak areas of low pressure traversing a boundary well offshore with perhaps some consolidation near New England Tue night and Wed. Confidence is a little higher that vigorous shortwave energy will move across the eastern Carolinas and provide ample lift Tue night and Wed before moving offshore Wed eve. We continue to include mainly chance POPs for Tue night through Wed afternoon/eve, first starting across our inland most zones and ending lastly across the Cape Fear area. The column should be cold enough to support light frozen precipitation, at least for a portion of the time. We continue to advertise some light snow moving into NW zones Tue night and expanding across the entire area during the late night hours and on Wed before ending Wed eve. The column will take some time to moisten and this looks like a low QPF event to begin with. Also, the column may not support frozen precipitation during the heart of Wed afternoon when the greatest coverage of precipitation may occur. Thus, from this vantage point, any accumulation of snow should be very light and perhaps just flurries. We will continue to monitor as models will eventually congeal on a plausible solution in regards to where and when coastal low development will occur. Highs Tue may sneak back up to near 50. The peak of the cold air advection this period should keep highs closer to the upper 30s to around 40 Wed and Thu with some temp recovery likely on Fri and this trend will continue into the upcoming weekend. Lows will be in the upper 20s to lower 30s Tue night. Lows will drop to the teens for most of the area Wed night. Wind chill values will be in the single numbers late Wed night and Thu morning. Perhaps not as cold Thu night, mainly 20s although a few teens will be possible. Lows Fri night should be in the upper 20s to mid 30s and temps Sat night should remain above freezing. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... As of 00Z...Latest satellite imagery indicated MVFR cigs exiting the coast. Surface high pressure will build west to east across the Great Lakes through Sunday, and winds will veer from NNW to NNE through Sunday. Extended Outlook...Some potential for MVFR/IFR/wintry precipitation Wed, otherwise VFR. && .MARINE...
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NEAR TERM /THROUGH SUNDAY/... As of 738 PM...Winds and seas will pick up overnight, leading to full SCA conditions, no changes were needed with the evening update, as the forecast incorporates these trends. As of 300 PM Saturday...Offshore flow has weakened a bit but will veer to northeast this evening with development of northeast cold surge expected. Northeast flow will end up right around 25 kt overnight, keeping seas over 6 ft for much of the nearshore waters, thus the SCA continues for all zones. Northeast flow continues on Sun but the gradient will start to relax during the second half of the day. Winds will still be close to 20 kt as the period ends which will keep seas greater than 6 ft for a large portion of the area. Anticipate SCA headlined for all zones through the end of the period. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 300 PM Saturday...Cold and dry high pressure will continue to extend down into the waters from the north. Winds will remain out of the north, but will begin to diminish Sun night into Monday leaving 10 kts or less of wind by Mon aftn into early Tues. Winds and seas will start out elevated with 10 to 20 kts of wind contributing to seas up to 4 to 6 ft, mainly in the outer waters Sun eve. The downward trend will allow a Small Craft Advisory to expire before midnight Sun night, although precautionary headlines may follow through early Monday. A small and temporary spike in the winds may occur around daybreak Mon as a shortwave moves through, but overall expect seas down to 3 to 5 ft Mon morning and 2 to 4 ft late Mon into early Tues. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Small Craft Advisory conditions may develop Wed into Thu. A wedge of high pressure will break down inland on Tue. A coastal front is expected to be in place offshore Tue. Still unclear as to whether an area of low pressure will be able to close offshore of the Carolinas. Arctic high pressure will build across the waters late Wed night and especially on Thu. N winds at the start of the period should back to a W or SW direction Tue afternoon and night. The wind direction is expected to then veer to NW early Wed and to remain NW through the remainder of the period. Wind speeds will be highest Wed night into Thu, up to 20 to 25 kt. Wind speeds will be less than 10 kt Tue and then slowly increase Tue night and Wed. Seas will be 2 to 4 ft Tue into Wed, building to 4 to 6 ft during Wed and Wed night before subsiding to 2 to 4 ft later Thu.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until midnight EST Sunday night for AMZ250-252-254-256. && $$ NEAR TERM...III/8 SHORT TERM...RGZ LONG TERM...RJD AVIATION...CRM

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