Area Forecast Discussion
Issued by NWS Wilmington, NC

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469 FXUS62 KILM 201035 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 622 AM EDT Wed Mar 20 2019 .SYNOPSIS... Weak low pressure off the coast will slowly move onshore today into Thursday spreading rain and breezy conditions over the area. A drying trend will begin later Friday and continue through the weekend as high pressure builds in from the northwest. Low pressure and a cold front will spread clouds and rain into the Carolinas late Monday into Tuesday. && .NEAR TERM /THROUGH THURSDAY/... As of 3 AM Wednesday...A deepening, oceanic pressure feature will undergo amplification today, carving a sharp trough axis offshore that approaches Cape Fear at 3z/11p. Already in the KLTX VWP, we are seeing 30 knots of NE wind at 2000 feet, and E-SE trajectories from 925-800 mb reflected, which is helping to guide a broken line of marine showers, with embedded moderate downpours landward, 60-80 NM offshore presently. The SHRA-line represents the trough-axis itself commencing a deepening trend, while shifting landward. The resultant pressure gradient from interaction with a strong wedge of high pressure, will produce brief gales offshore, while making for a windy day at beaches, especially SE NC. Low-level stability to remain strong, aided by evaporative cooling in initial virga, such that, from 18z today through daybreak Thursday, hourly temps may steadily fall. Nonetheless there are signals of a low-end spike in MU/MLCAPE along the coast and offshore to warrant a slight chance of a TSTM tonight. Since the trough axis may never make it to land, any convection offshore would become more elevated and detached from surface on encountering the wedge, a phasing to stratiform type rain inland. Hazards include wind gusts in excess of 40 mph possible at SE NC beaches and ICW. Strong spring tides will bring minor coastal flooding and high water run-up at high tide this morning, and an advisory is posted along beaches, all beaches given the approaching elevated low-level winds. System pulls away early Thu, pop/winds on the downtrend. Near seasonable high Thursday, and dewpoints to take a nice climb this period as moisture is thrown ashore. && .SHORT TERM /THURSDAY NIGHT/... As of 3 AM Wednesday...Mid-level trough axis will be swinging through as the period begins. Moisture at the base of the trough may eek out a weak shower during the first part of Thu night given fairly steep mid-level lapse rates, but the abundance of dry air makes the chances for measurable rainfall rather low for most areas. Virga is more likely, but given the nocturnal timing it would be hard to see any. Remainder of the period will be about deep northwest flow, very dry air, and 2 shots of cold air. The first, on Thu night, is more mild and drops temperatures near climo for Fri. Reinforcing shot of cold air arrives Fri night, dropping temps below climo for the end of the period. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 3 AM Wednesday...Shortwave mid-level ridge develops over the Southeast Sat into Sun. This feature moves off the coast early Mon as shortwave drops south out of central Canada. The shortwave helps induce troughing over the eastern CONUS, leading to a more active pattern as the period ends. -High pressure building in from the west for the weekend with temperatures below climo Sat rising to near climo Sun. -High moves farther offshore early Mon with increasing deep southwest flow increasing warm/moist advection over the Southeast. -Shower chances are limited Mon afternoon but increase Mon night as cold front arrives. Confidence is low given long time ranges. -Very low confidence Tue given lack of agreement between medium range guidance. For now maintaining unsettled but warm conditions. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... As of 12Z...A coastal low is expected to develop this morning just off the South Carolina coast and will move northward across southeast North Carolina later this morning and afternoon before shifting to the north. This system will bring MVFR ceilings and visibility`s to the coastal TAFs this morning and IFR ceilings to the the area at KILM by late morning and afternoon for the coastal TAFs of South Carolina. The best chances for rain is at KILM and lesser at KMYR and KCRE. Farther inland the rain chance diminish with VCSH possible at KLBT and KFLO. Extended Outlook...MVFR late Wednesday into Thursday with exiting storm system. VFR returns Friday into weekend as drying commences. && .MARINE... As of 3 AM Wednesday...Dangerous marine period upcoming as winds and waves increase in response to a coastal trough deepening and interacting with a strong wedge of high pressure as it nears Cape Fear tonight. This has prompted GALE flags from Little River Inlet northward today, SCA flags to the south. Large offshore waves will form due to the intense E fetch on the seaward side of the deepening trough, generating E waves 8-9 feet every 9-10 seconds today and tonight before decreasing in amplitude Thursday. Surfers to hit the waves Thursday in residual wave energy and offshore wind flow. A extended period of SCA may be required into Thursday as seas recover offshore. Isolated TSTMs possible tonight, to make treacherous marine conditions even more perilous, and navigation offshore is discouraged. SSTs 55-58 degrees inshore currently. High pressure will build over the waters from the west-northwest late in the week and into the weekend. Increasing offshore flow will follow a pair of cold fronts, the first moves offshore late Thu night with the second passing late Fri night. Although there will be some cold advection following each front, the gradient will not be particularly tight and speeds are likely to remain under 20 kt into Sat. Seas in the 3 to 5 ft range Thu night into early Fri will steadily drop in response to offshore flow. High moves overhead during the weekend with winds becoming light and variable. Seas will be 3 ft or less by Sat morning, dropping to 2 ft or less Later Sat and for Sun. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Coastal Flood Advisory until 10 AM EDT this morning for SCZ054- 056. NC...Coastal Flood Advisory until 10 AM EDT this morning for NCZ106- 108-110. Coastal Flood Advisory until 11 AM EDT this morning for NCZ107. MARINE...Small Craft Advisory until midnight EDT tonight for AMZ254- 256. Gale Warning until 3 PM EDT this afternoon for AMZ250-252. && $$ SYNOPSIS...III NEAR TERM...MJC SHORT TERM...III LONG TERM...III AVIATION...7

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