Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 180440 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1240 AM EDT Sun Mar 18 2018 .SYNOPSIS... Mild temperatures will prevail tonight ahead of an approaching cold front, that will cross the coast early Sunday. Lingering clouds and slightly cooler temperatures will be featured on Sunday. A warming trend can be expected early next week as a storm system approaches. Periods of rain and showers Monday night through Wednesday, may transition to light snow Wednesday night before drier air sets in Thursday. Accumulations are not expected because of the relatively warmer ground. A low pressure system will approach the coast next weekend. && .NEAR TERM /THROUGH SUNDAY/... As of 1000 PM Saturday...Concern overnight involves a potent shortwave evident on WV imagery moving overhead the Appalachians, and how its interaction with a surface cold front will impact convection overnight. Latest regional mosaic shows an area of strong to severe thunderstorms cresting the TN/NC/SC mountains and moving quickly to the ESE. This is in response to the aforementioned shortwave, and Although SPC has dropped the SLGT risk to our north, the MRGL risk has been expanded to include the extreme northern tier of the CWA. While the potential exists for thunderstorms overnight, it appears the severe risk is low due to the elevated nature of instability. Latest RAP soundings show 600-1000 J/kg of MUCape for parcels near 900mb, enough to sustain convection, but a stable surface layer should preclude any of the strong winds aloft from mixing down. However, there is a small area, mostly from Lumberton to Wilmington, where the high-res guidance suite, including the RAP, HRRR, NSSL WRF, and ARW, all paint some convection moving across beneath the upper vort and along the front. This is due to a ribbon of the slightly better instability correlating with higher moisture content and stronger forcing. Have increased POP to mid-chc northern tier and schc along the SC/NC border, but again, the severe threat looks minimal. Cannot rule out an elevated hailer, but the primary threat will be briefly heavy rain and some lightning, focused from about 2am near Lumberton, to 7am near Wilmington, and then moving offshore. A weak surface wave beneath the potent vort will exit offshore very late tonight or early on Sunday, and this will act to pull the cold front to the south. Behind this front temps will drop quickly and some stratus will develop, but exactly where this front settles will determine the sharp temperature gradient due to much warmer (cooler) temperatures on the south (north) side. Have tried to show this with upper 40s by daybreak Sunday far northern tier, while remaining in the mid 50s near the South Santee River. Relevant portion of previous discussion below: As of 344 PM Saturday...Southwest winds will veer around to the north behind front as it drops south through the area early Sun morning. Any lingering chc of pcp through the morning will lead to drying by Sun afternoon. Pcp water values up near 1.4 inches ahead of the front will drop to near a half inch air mass clears out in drier northerly flow as high pressure builds in. Max temps on Sunday will be near 60 over SE NC, but will reach closer to 70 in NE SC. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 344 PM Saturday...ECMWF/GFS both show an upper low across the Central Plains Sunday night. The upper low is progged to translate across the MS Valley during Monday evening. At the surface, a cold front will be aligned south of the forecast area at the onset. In the meantime, an area of isentropic lift and increasing low-level theta-E advection will bring rainfall chances back into the area Sunday night. Mentioned a slight chance of thunderstorms as well with some elevated instability present late Sunday night into Monday morning, primarily for SC zones. By early Monday evening both GFS/ECMWF position a surface low across TN with the warm front returning north across the area with decent rainfall chances continuing. Included thunderstorms during this time frame as stability decreases across the area. The ECMWF tracks the low a little further south, but given either solution our rainfall chances will be on the high end across the forecast area. Blend of MAV/MET numbers appears reasonable through the period. Would not be surprised to see the convective risk areas shifted a little farther north for Monday, but the bulk of the instability will likely stay farther south. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 344 PM Saturday...Low pressure pulling off the coast will bring a lull Tuesday, before another low develops and brings periods of showers Tuesday night through Wednesday, changing over to snow or a rain/snow mix Wednesday evening. Forecast low temperatures and thermal profiles, depict a brief period of frozen precipitation is possible across much of the area. Sharp mid- level drying will end PCPN prior to daybreak Thursday. Significant accumulations are not expected due to warmer ground, but a "Frost` advisory, or `Freeze Warning` may be needed very early Thursday, favored over interior SE NC, but could reach into parts of NE SC. Did not include thunder this period because of stable/cooler low levels, but elevated instability will exist to some degree. QPF Tue- Wed night averages to 3/10" to 5/10". && .AVIATION /06 UTC SUNDAY THROUGH THURSDAY/...
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As of 06 UTC...A frontal boundary stretches from south of KHSE to south of KRDU and to a low pressure center near KHKY. As an upper level shortwave moves across this boundary overnight the frontal boundary will shift again to south of KMYR and KFLO taf sites. Elevated convection is possible but expected farther north of KLBT and KILM and the South Carolina TAF sites are expected to remain precipiation free overnight. As the frontal boundary shifts south a few hours of IFR ceilings is expected mainly after 09 UTC and clearing by 13 UTC as there will be drying aloft boundary layer mixing during the morning. Extended outlook...Periods of MVFR Sunday through Wednesday. Chances for convection increasing Monday through Thursday.
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&& .MARINE... NEAR TERM /THROUGH SUNDAY/... As of 1000 PM Saturday...Front to the north will waver in the vicinity until a shortwave and weak low pressure move along it and offshore by the morning. This will drag the front southward and turn winds to the N/NW. However, this is not likely to occur until first thing Sunday, and most of the local waters will remain entrenched in gusty SW winds of 15-20 kts through the overnight, persisting seas at 3-5 ft. Relevant portion of previous discussion below: As of 344 PM Saturday...Winds will veer around toward daybreak quite rapidly to the W-NW and then N, with speeds increasing after a brief reprieve back to 10-15 kts. Seas will basically be in the 2 to 4 ft range, but expect a few 5 fters in the outer waters off of Cape Fear heading out toward Frying Pan Shoals. Looks like seas should remain below any criteria for SCEC or SCA. SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 344 PM Saturday...Weak high pressure across eastern NC at the beginning of the period will shift eastward Monday morning. A stalled front south of the waters will begin to lift north as another area of low pressure takes shape across the MS Valley. The initial easterly wind will veer to a southeasterly direction Monday morning. Additional veering is expected as low pressure moves across NC Monday night. Thus a stronger southwest fetch will develop with Small Craft Advisory conditions possible overnight Monday. Seas will be highest in the southwest fetch late Monday night. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 344 PM Saturday...This is shaping up to be a difficult marine period, as a series of strong low pressure systems impact the coast. Gusty SW winds 20-25 KT Tuesday and Tuesday night, will shift to north equally strong, if not stronger Wednesday as N and NW winds kick up in a cold air surge. Gusts to near Gale force are not out of the question Wednesday over the outer waters, with current numerical wave guidance at FPSN7 assigning 7 feet Wednesday. Very cold temperatures will greet mariners early Thursday, in a moderate, but biting, offshore wind. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...JDW/RGZ SHORT TERM...SRP LONG TERM...MJC AVIATION...RH is the U.S. government's official web portal to all federal, state and local government web resources and services.