Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 290033 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 833 PM EDT Tue Mar 28 2017 .SYNOPSIS... Showers and an isolated strong thunderstorm remain possible this afternoon ahead of a cold front which will move through late tonight. Relatively cooler and drier high pressure will build in from the north late Wednesday into Thursday. Showers and thunderstorms are expected as warmer and more humid air returns Friday ahead of a cold front which will move offshore early Saturday. Some of the thunderstorms may be strong to severe Friday and Friday night. The weekend should be dry as high pressure takes hold. Then early next week, a southern stream system will again bring the risk for showers and thunderstorms. && .NEAR TERM /THROUGH WEDNESDAY/... As of 3 PM Tuesday...A second shortwave is crossing the Carolinas this afternoon and with the early shortwave there has been a delay in additional convection developing. The GOES-16 1-minute imagery is showing cumulus developing west of Florence to Pembroke and isolated cumulus developing to the west. The 16 UTC HRRR is only showing isolated convection through sunset. So will keep a 20 to 30% chance of convection with the higher chances for the northern coastal areas. The frontal boundary will shift across the area after midnight and sweep to the south with high pressure building in the area into Wednesday. Lows tonight are expected to fall into the upper 50s and highs on Wednesday to around 80 except cooler at the beaches with a northeast flow. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...Mid level ridge axis over the southeast will be deamplifying and shifting east Wed night as surface high over southern Canada builds down the east coast. Cooler air associated with the Canadian high spreads over the region Wed night with lows dropping close to climo. Northeast winds will be in the 5 to 8 mph range which should prevent any radiational cooling. Low will be in the low to mid 50s across much of the area. Surface high shifts off the coast later Thu with weak return flow developing Thu night. Ridging aloft Wed night and Thu will keep the region dry through at least Thu evening. Forecast soundings show impressive subsidence from 850mb through 700mb into Thu night before approaching high amplitude southern stream system shunts the 5h ridge axis farther off the coast. Developing deep southwest flow Thu night increases moisture in the region, precipitable water values increase from around 0.80" Thu evening to 1.40" by the end of the period. Arrival of this deeper moisture along with an increase in mid level lapse rates should open the door for some convection late in the period. The unfavorable timing and lack of strong low level jetting does suggest coverage will be rather limited and do not plan on much in the way of changes to inherited Thu night precip chances. Temperatures Thu will be near to slightly below climo, upper 60s to lower 70s, with temps Thu night running above to well above climo and likely following an atypical curve with slight warming after midnight. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 AM Tuesday...Next in series of potent southern stream systems will impact the eastern Carolinas Fri and Fri night with a categorical risk for showers and thunderstorms developing. The combination of significant upper level support and strong and deep moisture return and lift provides at least the opportunity for a more widespread and significant rainfall event. There will be some risk for strong to severe thunderstorms during this time. 0-6 km effective bulk shear parameters are not particularly impressive. However, instability does grow with mixed layer CAPE values on the order of 500 to 1000 J/kg as the warm front should move to our N. Mid-level lapse rates are forecast to be rather modest. The potential is there for an active day/night leading into the weekend, although magnitude is certainly still a question mark. In the wake of this system, dry weather and near to above normal temps are expected for the weekend as mid-level ridging builds across the area and surface high pressure builds from the NW and N. Attention then will turn westward as next southern stream system along the Gulf Coast Sun night lifts to the NE and drags a warm front to the N. This will again bring deep moisture into the Carolinas, and with that, showers and thunderstorms early next week. Given timing differences between long range models and a general slower trend as compared to 24 hours ago, will cap POPs in the chance category until we can gain better resolution as to when the highest risk for showers and thunderstorms will occur. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 00Z...Sfc convergent boundary lies along an east to west line extending from Surf City across Whiteville to Hartsville. This feature is a product of storm outflows and the sfc cold front sinking southward. Isolated low topped showers and possibly a thunderstorm will likely continue to develop along this boundary as it sinks southward for the next few hours. With subsidence aloft, do not expect much vertical development. Will only carry VCSH for the associated terminals near this boundary. The remainder of the night will see improving ceilings and winds that slowly veer from SW-W to NW-N overnight...and to the NE during Wed. Wind speeds mainly 5 to 10 kt early this evening, dropping to 2 to 4 kt overnight after the CFP. None of the near term guidance is illustrating fog development for the pre-dawn Wed hrs. May place patchy MVFR fog at press time or amend later on this evening if 00Z Model guidance shows it. No ceilings or pcpn for daylight Wed. Only concern will be the slow veering wind direction trend from NNW-NNE at sunrise to ENE to E at sunset. Wind speeds thruout the day at 5 to 10 kt. The coastal terminals may see an aftn/early evening seabreeze develop with winds from the SE around 10 kt. Extended outlook...VFR conditions Thu. MVFR/IFR conditions likely in showers and strong to severe thunderstorms Fri/Fri night. VFR conditions Sat thru Sun.
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&& .MARINE...
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NEAR TERM /THROUGH WEDNESDAY/... As of 3 PM Tuesday...SW winds around 15 knots with higher gust are seen at coastal CMAN stations...not receiving any offshore buoy data at this minute so have lower confidence of the current wind speeds at 10 to 20 miles off the coast. With cold front approaching expect to see winds increase to 15 to 20 knots with higher gust. Seas are expected to peak at 3 to 5 feet. Will continue to see longer period swells through this evening. With the cold frontal passage expected between 2 AM and 6 AM Wednesday, seas will slowly fall to the 3 to 4 feet range by the end of Wednesday. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 3 PM Tuesday...Northeast flow will continue Wed night and Thu as high pressure over southern Canada builds south. Gradient becomes pinched late Wed night as cold surge moves across the waters and northeast flow may briefly hit 20 kt. Northeast flow remains 15 to 20 kt Thu before starting to decrease and veer to east Thu evening and then southeast Thu night as the surface ridge axis moves offshore. Seas will range from 3 to 5 ft through Thu night with shorter wave periods expected given the strength of the northeast flow. Exercise caution headlines may be needed during the period, depending on the strength of the northeast surge late Wed night. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 AM Tuesday...A Small Craft Advisory is likely for all waters Fri and Fri night with conditions possibly lingering into Sat. Slow moving area of low pressure will be moving across the Ohio Valley Fri. Its accompanying warm front will move across the waters Fri. As low pressure moves offshore of the Mid-Atlantic states late Fri night and Sat morning, it will strengthen and drag a cold front across the waters. High pressure will slowly build across the area from the N and NW Sat night and Sun. SE winds Fri morning will become S and then SW Fri night. The wind direction will become westerly early Sat morning and then NW by Sat afternoon. N winds Sat night will become NE overnight Sat with NE winds persisting into Sun before veering to easterly during the afternoon. The strongest winds are expected Fri and Fri night, up to 20 to 25 kt. Seas late Fri and Fri night will build to 4 to 7 ft and around 8 ft at frying Pan Shoals. Seas during Sat will only slowly subside as backswell from departing storm system impacts the waters. Seas should drop below advisory levels by late Sat and to 2 to 4 ft on Sun.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DRH NEAR TERM...DRH SHORT TERM...III LONG TERM...RJD AVIATION...DCH

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