Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 091955 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 255 PM EST Sat Dec 9 2017 .SYNOPSIS...
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Cloudy skies will gradually clear this evening and overnight as low pressure moves away from the area. Sunshine returns Sunday, but with continued chilly air as Canadian high pressure builds eastward. A strong cold front will cross the area Tuesday night with Arctic air returning Wednesday. Temperatures gradually moderate Thursday and Friday before another cold front brings cooler temperatures for next weekend.
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&& .NEAR TERM /THROUGH SUNDAY/...
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As of 3 PM Saturday...This has been the coldest day since January 7th for most sites across the eastern Carolinas with temperatures stuck in the upper 30s to lower 40s. A strong upper level disturbance is passing across the central Carolinas now and should move off the coast this evening. One final band of lift and reasonably deep moisture is squeezing out one or two hundredths of an inch of precipitation as far south as Columbia, SC. Precipitation as far south as Charlotte, Monroe, and Asheboro is falling as snow as the very persistent warm nose we`ve had throughout this multiday event is finally eroding. Light rain should fall near and west of I- 95 for a few hours late this afternoon, with precipitation wrapping up around dark in the Lumberton area. While it`s not impossible that some wet snow could mix in at the end of this precip event, RUC forecast soundings show we lose saturation at the -12C level before the 850 mb warm nose erodes, making snow unlikely this far south. Better luck with the next storm system! Linear extrapolation of the back edge of the low clouds across South Carolina matches quite closely with RUC/HRRR/NAM depictions of loss of high relative humidity in the 950-850 mb layer this evening. Rapid clearing should sweep west to east across the Pee Dee Region from 7-9 pm, reaching the SC coast an hour or so later and the Cape Fear region before midnight. Cold advection surging in on west- northwest winds will bring freezing temperatures all the way down to the coast tonight with upper 20s expected inland and lower 30s on the beaches. We`re well beyond the climatological date for the first fall freeze, so no freeze products will be issued for this event. Sunny and chilly conditions are expected Sunday as Canadian high pressure builds eastward along the Gulf Coast. Highs should only reach the upper 40s, a bit below GFS/NAM guidance but in-line with the ECMWF.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/...
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As of 3 PM Saturday...Local area will remain at the base of a broad mid to upper trough over the eastern CONUS with an almost zonal flow through much of the period. At the surface high pressure to our south will nudge eastward with light SW to W winds through Sun night into Mon. This will allow a slight warming with temps reaching back toward normal after a very cold start Mon morning. The next shortwave will dig south later on Mon into Mon night. This will push a sfc low east with winds backing to the S-SW and increasing slightly allowing for some moisture return late Mon into Mon night. Dewpoint temps will increase from the mid 20s Sun night to the mid 30s Mon night. Sun night will have better radiational cooling conditions with lighter winds and clear skies. Temps will drop down to the mid to upper 20s most places Sun night, and lower 30s along the coast. Temps will attempt to recover on Mon in light S-SW flow and plenty of sunshine, with most highs reaching into the mid 50s. By Mon night the slight increase in SW flow will keep temps about 10 degrees warmer than previous night with mid 30s inland to lower 50s along the coast.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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As of 3 PM Saturday...A series of shortwaves will cross the area during the period, dragging a couple cold fronts with them. The first arrives on Tue. Lack of deep southwest flow ahead of the wave, compliments of the 5h longwave trough, will prevent the wave from generating little more than an increase in cloud cover. Although the front crosses the area during the day temperatures will run near to slightly above climo. The cold air arrives Tue night dropping temperatures well below climo for the middle of the week. Change in 850 temps from Tue to Wed is almost 15C, +3C to -11C. Highs Wed will struggle to reach mid 40s despite full sun should that verify. Next shortwave crosses the area Thu morning, again starved of moisture, and lacks any cold air. Wave exits northeast on Thu as the 5h trough starts to flatten ahead of the next, stronger shortwave. As the 5h trough amplifies to the west, deep southwest flow will develop over the southeast, pushing temps closer to climo. Duration of the return flow is brief and precipitable water values barely reach half an inch. Clouds will increase Thu night as the wave approaches and then passes early Fri morning. Not sold on any measurable precip based on moisture profiles despite the strength of the feature. Cold front trailing the wave quickly crosses the area and shifts offshore early Fri, bringing another round of cold advection to the region late Fri. Advection arrives too late to have a big impact on highs for Fri, but Fri night temperatures will drop below climo. Although this air mass does not look as cold as the one during the middle of the week, temperatures for the end of the period will still be close to 10 degrees below climo.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... As of 17Z...IFR cigs are expected to persist well into the afternoon hours before transitioning to VFR between 00Z and 04Z as westerly winds scour out low clouds and moisture. VFR then expected for the remainder of the TAF period. N to NW winds of 5 to 10 KT today will become W to NW tonight. Extended Outlook...VFR through Thursday. && .MARINE...
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NEAR TERM /THROUGH SUNDAY/... As of 3 PM Saturday...Low pressure moved northward along a cold front a couple hundred miles off the coast earlier today. The front is now moving farther off the coast, pushed by Canadian high pressure over the southern Plains states. This high will build eastward along the Gulf Coast region tonight into Sunday with continued offshore winds here across the Carolinas. A strong upper level disturbance will push off the coast late this evening. This feature will help produce a surge of west-northwest winds with gusts to 30 knots possible overnight. Small Craft Advisories will remain posted overnight into Sunday morning until winds diminish below 25 knots. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 3 PM Saturday...High pressure to the south will move east as next system begins to drop toward the Carolinas by the end of the period. This will maintain lighter SW-W winds Sun night into Mon with winds 10 to 15 kts and seas 2 to 4 ft through Mon. As next area of low pressure pushes a cold front toward the Carolinas late Mon into Tues, the winds will back and gradient will tighten to push winds and seas back up. Expect seas up to 3 to 5 ft by Mon night with SW winds up to 15 to 20 kts. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 3 PM Saturday...Cold front moves across the waters on Tue with offshore flow developing and then increasing as cold advection ramps up. Winds 15 to 20 kt at the start of the period will increase to 20 to 25 kt Tue night into Wed. Offshore component may keep seas within 20 nm of the SC coast under 6 ft but NC nearshore waters seem likely to hit 6 ft and possibly 7 ft at times. Cold advection and gradient slowly weaken on Wed with offshore flow gradually dropping to 20 kt around midday and 15 to 20 kt by the end of the day. Seas will mimic wind speeds, slowly subsiding Wed into Wed night. Flow remains offshore Wed night, before backing to southwest Thu and starting to increase as next cold front approaches from the west. Southerly flow will increase to a solid 20 kt Thu afternoon and evening with seas increasing from around 2 ft Thu morning to 3 to 5 ft Thu evening.
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&& .TIDES/COASTAL FLOODING... As of 1100 AM Saturday...A tremendous positive tidal anomaly has developed along the beaches north of Cape Fear over the past 24 hours, averaging 1.5 to nearly 2.0 feet at the Wrightsville Beach tide gauge! Even though astronomical tides are not particularly impressive, this anomaly should allow today`s noon high tide to create coastal flood thresholds along the beaches north of Cape Fear. An advisory has been issued through 1 PM. && .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Small Craft Advisory until noon EST Sunday for AMZ250-252-254- 256.
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&& $$ NEAR TERM...TRA SHORT TERM...RGZ LONG TERM...III AVIATION...RAN TIDES/COASTAL FLOODING...TRA

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