Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 200117 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 917 PM EDT Wed Apr 19 2017 .SYNOPSIS...
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A stalled and diffuse front in the vicinity of Charleston SC, will slowly dissipate as it tries to lift north as a warm front late tonight and Thursday. The Bermuda High will expand west over the region Thursday through Saturday. A low pressure system and associated cold front will move through the Carolinas late Sunday into Monday, with low pressure possibly lingering off the U.S. Southeast coast thru Tuesday. High pressure will build in slowly behind departing low Tuesday through Wednesday.
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&& .NEAR TERM /THROUGH THURSDAY/...
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As of 845 PM Wednesday...The sea breeze induced convection has dwindled to just isolated showers at the moment, and should be all clear within the the next 1 hour. Convective debris cloudiness will thin or scour out during the remainder of this evening and overnight. This will allow for radiational type fog to develop especially across areas having received rainfall today. The problem facing the FA overnight will be the extent of the fog and whether it reaches dense criteria. And a side note, of whether low level stratus develops. For now, have followed previous thinking with fog at its worse inland. Will remain somewhat suspect of the low stratus deck, but if it occurs it should be around 1.5k ft or lower. Low temps tonight look aok with no tweaking needed. Previous...................................................... As of 300 PM Wednesday...Fairly widespread shower activity has lit up just inland from the coast along the seabreeze front. This activity has developed within an uncapped airmass with CAPE around 1000 J/kg and very little steering flow. Showers should exhaust their fuel in the next several hours and dissipate with the setting of the sun. A weak and diffuse front stalled across southern South Carolina should begin to move northward tonight as high pressure over the Canadian maritime provinces pulls off to the northeast. This boundary will move overhead between midnight and 5 AM, however winds here at the surface should be decoupled and we won`t immediate notice the front`s passage. Another consequence of the decoupled boundary layer tonight is likely to be fog. Moisture advection with today`s onshore flow plus this afternoon`s shower activity should yield areas of fog by midnight. Fog could become dense at times, although the shallow depth of the decoupled boundary layer argues for a quick burnoff Thursday morning. Thursday will seem almost summerlike with light southwest winds and mainly sunny conditions in the morning turning partly cloudy and warm with scattered showers during the afternoon. A moderate seabreeze circulation should develop, helping to concentrate showers essentially over the same regions that have picked up rain today. A somewhat stronger west-northwesterly mid level flow could help push showers across the seabreeze and back down toward the beaches by late afternoon, and I have included PoPs as high as 30 percent for Wilmington and Myrtle Beach as as result. Highs Thursday should reach the mid 80s inland with upper 70s to lower 80s at the coast.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...Potentially the hottest temperatures so far of 2017 expected Friday as low-amplitude but strong ridge builds across the southeast. Surface high offshore will create warm SW return flow, driving 850mb temps up towards 14C Friday. This occurs in conjunction with W/NW mid and upper level flow, which is typically a dry and warm flow aloft, further adding to the heat potential. The MOS guidance is all within a degree or so, and expect widespread mid-80s with upper 80s across the Pee Dee. In fact, a few spots may touch 90 well inland for the first time this year. ALong the coast, a sea breeze will develop but not before most places at least touch 80, the exception being the typically cooler Brunswick County coast where highs will struggle into the mid 70s. The same airmass responsible for this heat will keep mins elevated both Thursday night and Friday night as well, dropping only to a degree or two either side of 65 both nights. A cold front will approach slowly from the NW late Friday night, but most of the guidance suggests it will hold off until beyond this period before creating any showers or even much in the way of cloud cover. Feel this slower solution is more likely as its motion gets impeded both by boundary parallel mid-level flow, as well as orthogonal surface flow impinging on the front from the south, and will drop POP to silent until very late Friday night, and even then only include SCHC for far NW zones. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday...Deep southerly return flow around the Bermuda High with ridge aloft will bring very warm weather for the weekend. The models have been consistently showing a backdoor cold front reaching into NC and may be nearby early Sat with the GFS being the most aggressive with the southward push. It looks like this boundary should remain far enough north as to keep most associated weather north of the forecast area for now. A low pressure system moving west through the southern CONUS will push this front back north by late Sat into Sun leaving the coastal Carolinas in a continued warm and moist south to southwesterly flow. Pcp water values along this front to the north will be up to 1.6 inches but down near 1.25 inches in most of our local forecast area through Sat and diminishing further through early Sun. Overall expect the development of some cu and potential for localized showers on Saturday if boundary stays north, but will include clouds and pcp over northern tier to account for front in vicinity. Sunday should start off dry with increasing clouds through late Sunday as cold front approaches from the west. Best chc of showers and thunderstorms will come late Sunday west zones and into Sunday night for coast, but should be fairly widespread coverage with strong to possible severe storms in a very warm and moist air mass ahead of front. Cooler northerly flow will advect drier air into the area on the back end of the low, but the low will linger right off the coast with clouds and pcp remaining on Monday and possibly into Tues. The greatest chc for pcp will be closer to the coast especially as the low pulls slowly away late Mon into Tues. Drier high pressure will build in behind the departing low Tues into Wed. Temps will reach into the 80s except right along the coast both Sat and Sun, but Mon will cool down to near 70. A slight warming will occur through mid week bringing temps up near normal again. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... As of 00Z...The sea breeze induced convection will pretty much come to an end once sunset occurs and nightfall settles in. Will include VCSH for LBT terminal based on the latest 88D pcpn trends. Convective debris clouds will dominate the evening sky but should dissipate or scour out quickly during this evening. The next obstacle to tackle for aviators during the pre-dawn Thu hours will be the potential for fog and how widespread and deep in the vertical will it become. With increasing moisture in the lower levels and winds becoming nearly calm across all terminals, radiational type fog looks like a good bet. With leftover convective debris clouds scouring out by midnight, will indicate fog developing there-after and persisting up to 1-2 hrs after daybreak. The inland terminals will potentially see dense fog during the pre-dawn hrs. For the coastal terminals, took the more optimistic route and kept the dense fog possibility out of the fcst, for now. CRE terminal always likes to go against guidance when it comes to fog possibilities, and it`s usually for the worst case scenario. For now, will indicate down to 2sm. For daylight Thu, will see another sea breeze induced convection day. It`s inland progression may be limited and thus held out from mentioning any convection for the 2 inland terminals. The center of high pressure overhead tonight will become re- established offshore from the SE U.S. coast on Thu. Looking at nearly calm winds tonight becoming W to SW during Thu. A light increase to the sfc pg will result in 5 to 10 kt sustained winds during Thu. Extended outlook...MVFR/IFR conditions possible in showers and TSTMS Saturday through Sunday night. && .MARINE...
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NEAR TERM /THROUGH THURSDAY/... As of 845 PM Wednesday...Winds from Cape Fear northward remain active from the E around 10 kt. South of the Cape, southeast to south at 10 kt or less. Winds overall will be veering as the elongated center of high pressure overhead, becomes re-established offshore from the SE U.S. Coast by late Thu. The sfc pg remains relaxed tonight and shows signs of some tightening during Thu. Significant seas overnight will range from 3 to 4 ft from Cape Fear northward, with 2 to 3 ft south of the Cape to South Santee River. An easterly psuedo swell at 7 to 8 second periods will be the primary input for the significant seas. Previous.................................................... As of 300 PM Wednesday...A weak front stalled across southern South Carolina will weaken as it lifts northward tonight. Easterly winds blowing as hard as 15 knots north of Myrtle Beach through the Cape Fear area this afternoon will settle back to only 5-10 knots as the front approaches around midnight, then should shift southwesterly late tonight into Thursday morning. This is all occurring as Canadian high pressure ridging down the East Coast begins to retreat off to the northeast. Wave heights have been kicked up in the Cape Fear area due to the stronger easterly winds in place most of the day. Frying Pan Shoals buoy is still reporting 6 feet, with 3-4 feet at the nearshore buoys. Thursday will feature an almost-summerlike pattern as light southwesterly winds during the morning increase substantially during the afternoon as a healthy seabreeze circulation develops. SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...High pressure offshore and a slowly approaching cold front from the NW will drive increasing SW winds through the period. Wind speeds Thursday night of 10-15 kts will increase through Friday, becoming 15-20 kts late in the period. Although an easterly swell from a distant subtropical depression, and a SE swell around the high pressure, will exist in the spectrum through the period, it will be increasingly masked by an amplifying SW wind wave. This wind wave will grow to 3-4 ft at 5 sec, and wave heights build from around 2 ft Thursday night, to 3-4 ft Friday night. LONG TERM /SATURDAY THROUGH MONDAY/... As of 300 PM Wednesday...South to southwesterly flow will persist around Bermuda High through the weekend. This southerly push will drive seas up to 3 to 5 ft late Sat into Sun. Wind speeds should be about 10 to 15 knots with a slight uptick and backing of winds each afternoon in sea breeze. A low pressure system and associated cold front will approach late Sunday into Sunday night. Winds will shift to the north behind the front and may increase up to 20 kts or so on the back end of this low as it lingers and begins to slowly depart Mon night. This northerly surge may produce small craft advisory conditions by late Mon.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...DCH/TRA SHORT TERM...JDW LONG TERM...RGZ AVIATION...DCH MARINE...

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