Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 181726 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1226 PM EST Sun Feb 18 2018 .SYNOPSIS... High pressure will build down from the north pushing a cold front through the area this morning. This front will return back to the north as a warm front on Monday. Bermuda High pressure will bring well above normal temperatures beginning Monday with possible record warmth mid week. A cold front will approach from the north on Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 930 AM Sunday...The front pushed south of Georgetown before sunrise this morning. Northeast winds will increase over the next couple of hours as the front stalls out across Georgia and southernmost South Carolina. Low clouds are burning off, but persistent mid-clouds streaming eastward across South Carolina will probably ruin any chance of a sunny day south of Florence and Myrtle Beach. This plays into temperature forecasts, which I`ve lowered slightly in those cloudier areas in South Carolina but have made little change elsewhere. Highs should reach the lower to middle 60s, except remaining stuck in the 50s on the beaches with the increasing northeast winds. Mid-level clouds should begin to lower and spread northward again late this afternoon as the stalled front starts to bow northward again. Discussion from 300 AM follows... Temps increased up near 60 over eastern half of forecast area in WAA as SW flow developed behind a warm front lifting inland and north. Temps inland were closer to 50 to 55 in NW- N flow as cold front was making its way south and east overnight. The area was plagued by fog and low clouds through the overnight hours. There were some breaks in the clouds in SW flow behind warm front, but as cold front drops south and east into and through the forecast area this morning, low clouds will return for a brief time. Forcing remains too weak for much of any pcp at all. Sounding data and moisture profiles show almost saturated column up through 7 to 8k ft as front drops south and show column drying out by mid to late morning from north to south. Winds will pick up out of the N to NE as high pressure builds in. High pressure will build down behind the cold front through today. As it reaches into SC, this front will lay flat as flow across the top of broad ridge extending from the Gulf of Mexico east well into the Atlantic, remains parallel to the front. Enough dry air will move in behind the front to produce a fair amount of sunshine through today, but the back edge of clearing may not make it through the entire forecast area. As the high to our north shifts off the Mid Atlantic coast later today, the winds will shift around to the NE to E. This will allow a return of moisture and expect clouds to increase once again. Portions of northeast SC may not clear too much before this on shore flow of marine moisture makes brings clouds back into the area. Overall expect some sunshine across the area with temps reaching into the mid 60s, but cooler at the beaches. The front will stall out south of the area today and will lift north as a warm front/coastal trough overnight tonight. This will produce an increase in on shore marine moisture and should see increase in clouds this evening and some weak isentropic lift to support some light pcp mainly after midnight tonight. Temps will be in the 50 to 55 degree range for lows overnight tonight, remaining on the mild side due to clouds and increasing warm and moist air. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure will be centered off the coast of southeastern New England Mon morning. A coastal warm front will extend up the Carolina coast early Mon and is expected to lift inland and across the Forecast Area during the day Mon. Expect mainly cloudy skies to hold across the area Mon morning with a pronounced near surface based inversion firmly in place. Some erosion in these clouds is expected Mon afternoon, lastly across inland areas. A very warm airmass will then build across the area with 850 mb temps climbing to 11-14C through the period. Dewpoints will also be unseasonably high, rising to the lower to mid 60s. Model soundings support fog/stratus development late Mon night into Tue morning and again late Tue night and have included patchy fog throughout during this time. Early morning fog should burn off readily, except perhaps for some of the beaches, where patchy fog may linger longer as conditions become marginally conducive for sea fog development. Can not rule out some patchy light rain Mon morning and perhaps a stray shower Mon afternoon or eve ahead of and in the vicinity of a warm front. Any measurable QPF will be isolated and have kept POPs in the slight chance category. We are not quite forecasting any record highs through Tue, but certainly temps will be warming to unusually warm levels for Feb. Highs on Mon will be mainly in the 70s. As warm as the upper 70s for portions of the area and as cool as near 70 for the beaches. Highs on Tue will be in the lower 80s inland with a temp gradient as you near the coast where the beaches should be stymied in the lower 70s due to a seabreeze. Lows will be in the upper 50s Mon night and mainly lower 60s Tue night. 2/19 City High Temperature Forecast/Daily Record High Wilmington 73/78 in 1976 Florence 76/80 in 2014 N Myrtle Beach 70/73 in 2017 2/20 City High Temperature Forecast/Daily Record High Wilmington 77/81 in 1991 Florence 81/83 in 2014 N Myrtle Beach 72/77 in 1949 && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 300 PM Saturday...An exceptionally strong upper level ridge is expected to develop next week off the East Coast. 500 mb heights up to 591 DM would be above normal in August, and should be among the highest values ever observed locally this early in the season according to the SPC sounding climatology webpage. The Penn State GEFS ensemble viewer (http:/cms.met.psu.edu/sref/GEFS) shows 500 mb height forecasts nearly 3 standard deviations above normal for several days next week. This should be a vertically stacked high with deep southerly flow transporting an unseasonably warm and humid subtropical airmass across the Carolinas. High temperatures are expected to reach 80-83 degrees Wednesday through Thursday inland, with somewhat cooler readings expected near the coast due to nearshore water temperatures still in the 50s. The warmest days are expected to be Wednesday and Thursday where record highs are currently forecast in Florence and Wilmington. Thursday should be the warmest day near the coast as an upper level trough passes through New England, veering surface winds a bit more westerly which will delay/suppress the seabreeze and its cooler, maritime influence. I think Thursday may have the best potential for Myrtle Beach to achieve a record high. As the trough passes through New England and Canadian high pressure advances eastward across the Great Lakes, a backdoor cold front will get shoved southward into the Carolinas Thursday night. To be a day 6 forecast there is surprising agreement among the GFS/ECMWF/Canadian models with the timing of this front. Cooler northeasterly winds behind the front should suppress temperatures by 5-10 degrees on Friday. As the ridge rebuilds again Friday night the front should return north with our temperatures rising well above normal again on Saturday. I`ve kept the forecast dry through the period as it appears each day`s cumulus field should be capped off by a subsidence inversion 6000-9000 feet AGL associated with the strong upper ridge. While it`s possible a sprinkle or light shower could develop from shallow diurnal convection beneath this inversion, coverage of rain should be less than 10 percent each day. The best potential for a shower might be on Wednesday as both the GFS and ECMWF show a pocket of enhanced mid-level moisture passing across the central and western Carolinas during the day. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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As of 18Z...Currently VFR. Northeast winds will veer to easterly later this afternoon as high pressure moves off the Mid-Atlantic coast. Winds will continue light east to northeast tonight. A warm front begins to return north overnight. Increasing low and mid level moisture and weak isentropic lift will bring MVFR cigs and patchy light rain into the terminals this evening. Overnight there is high confidence IFR cigs cigs will develop although confidence in timing is low attm. Precipitation should increase in coverage but it should remain light with weak forcing. LIFR cigs possible 11-15Z mainly coastal terminals as the frontal inversion lowers. Cigs increase to IFR mid to late morning with some MVFR possible. Extended Outlook...VFR with periods of MVFR through Fri. Good chance of extended periods of IFR/LIFR in sea fog coastal terminals Tues-Fri.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 930 AM Sunday...The cold front pushed south of Winyah Bay and the Santee River before sunrise. Fairly light north and northeasterly winds behind the front since should increase very soon near and north of Cape Fear to 15-20 knots with gusts near 25 knots this afternoon. The ramp upward in wind speeds may take a few more hours along the South Carolina coastline but deteriorating conditions should still develop by early afternoon. The `exercise caution` headline will remain on the forecast, and may even need to be extended a few hours later on the next update. Seas are currently 2-4 feet on the CORMP/NDBC buoys near Cape Fear, but should build by another 1 to 1.5 feet in short period chop this afternoon due to increasing winds. Discussion from 300 AM follows... Cold front will get pushed south and east through the waters this morning as high pressure builds down behind it through today. SW winds ahead of the front will veer around at this time to the W then NW and around to the N through this aftn. As the gradient tightens as the high builds in through this afternoon, winds will increase out of the NE up to 20 kts with higher gusts. This will push seas which are now 2 to 4 ft, up to 3 to 5 ft this afternoon. Therefore have included precautionary headlines through this afternoon for all waters. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...A coastal warm front will move across the waters Mon morning and then inland as it lifts to the N. Bermuda High pressure will build in its wake. Winds and seas look rather benign, especially given the time of year. E to SE winds early Mon morning will shift to S by early afternoon and then remain from the S through the period. Wind speeds are not expected to exceed 10 kt through the period. Seas will be 2 to 3 ft. The only hazard may be the development of sea fog. Dewpoints will be surging into the lower 60s Mon and then remain at those levels through the forecast period. Given water temps are still in the mid 50s, conditions will become marginally conducive for sea fog. However, the wind direction will be S, thus limiting residence time over the coolest shelf waters. Will include patchy sea fog in the gridded forecast beginning late Mon night and then show it persisting through the end of this forecast period. LONG TERM /WEDNESDAY THROUGH THURSDAY/... As of 300 PM Saturday...Strong high pressure will build off the East Coast next week, bringing gentle southerly winds Wednesday. By Thursday winds should veer more southwesterly in advance of a backdoor cold front that is expected to reach the Cape Fear area sometime Thursday night. This should be a very warm airmass, perhaps too warm for any sea fog to develop despite an otherwise favorable situation. A large region of easterly and southeasterly winds south of the big Atlantic high should produce a 9-second southeasterly swell that could reach 3 feet out at 20 miles distance from shore. Shorter period wind waves of 1-2 feet are also expected. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...TRA/RGZ SHORT TERM...RJD LONG TERM...MBB AVIATION...MRR

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