Area Forecast Discussion
Issued by NWS Wilmington, NC

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908 FXUS62 KILM 300821 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 421 AM EDT Fri Sep 30 2016 .SYNOPSIS... A stationary front will waver along the coast through this weekend. Periods of showers with an isolated thunderstorm are possible along this front. Weak high pressure will build in early next week. Hurricane Matthew may bring increasing waves by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Friday...The expansive cutoff Low centered over Kentucky will be the main show affecting the ILM CWA this period. The latest HRRR, RAP and HiResWrf models, all indicate to a degree, the current pcpn breaking out and further increasing in coverage and intensity during early this morning and continuing thruout the day. This a result of dynamics from elongated mid- level vorts from the tropics passing nearly overhead, the sfc frontal boundary aiding low level forcing, and copious amounts of moisture with flow from the sfc thru aloft mainly southerly straight from the tropics. With the days heating and sfc based instability becoming available, convection should breakout further. The dry slot/tongue rotating around the cutoff low, will slowly push the pcpn toward the east whereas the individual showers and storms will be racing to the north. The back edge of this main area of pcpn should push just east of the ILM CWA by early this evening. Locations especially west of the I-95 corridor, will actually see drier air and lower temps due to the dry slot. How much of this drier air and lower temps work eastward are 1 of the main challenges of this forecast. For the overnight period, have left a low POP along the immediate coast, basically in the vicinity of where the stalled frontal boundary ends up. At this point, have indicated in the Hazardous Weather Outlook that heavy rainfall from todays convection will have the potential to produce temporary flooding especially susceptible areas having experienced a good dose of rainfall during the past few days. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 345 PM Thursday...Little change in the synoptic setup into the weekend as bowling ball of the upper low spins slowly across IN/KY before lifting into OH late in the period. At the surface, a very slow moving cold front will push eastward, likely finally crossing offshore Friday night before stalling once again. With diffluence remaining east of the upper low, and low level confluence likely persisting along and east of the boundary, more convection with periods of heavy rain is forecast Friday. The best chance for rainfall will again be the eastern third of the CWA where mid-level RH remains elevated despite a very dry punch within the dry slot working into the Pee Dee. This creates 2 distinct air-masses across just the local CWA, with PWATS forecast to drop below 1 inch well inland, while remaining at 1.5-1.75 near the coast, and inland counties may finally have a dry day Friday. By Saturday, most of the CWA is forecast to get into the drier air, but once again the immediate coast may still see no relief from this humid airmass with more showers/tstms possible along the coast. Highs both Friday and Saturday are forecast to be slightly above climo, low 80s, but will be heavily impacted by clouds and rainfall. Mins inland will drop into the upper 50s/low 60s both nights within that drier air mass, but will remain near 70 at the coast. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 3 AM Friday...Temperatures will be quite seasonable to slightly mild and rain chances minimal through the long term. Moisture associated with frontal remains lingering offshore on Monday and low level onshore flow could advect the stray shower to mainly coastal areas. Weak upper troughiness may aid the coverage of showers even though mid levels probably dry. Beyond Monday this troughiness gets replaced by a slowly amplifying ridge and this should cut down on the already paltry radar coverage. This low coverage will be confined to coastal areas while inland zones stay dry. Low level moisture trapped beneath the inversion will favor a bit more in the way of clouds than `normal` through the period. Currently it appears that Matthew stays far enough east to only have marine effects locally. The GFS has been a very fast outlier from other guidance though now Canadian is even faster. The EC has shifted a bit farther east from previous runs. The overnight RI is allowing convection to wrap around the center and so models may show some improvement with the system stacking in the vertical. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... As of 06Z...Patches of IFR or lower now becoming less widespread ahead of approaching pre-frontal band of showers and should remain so for the rest of the overnight save for perhaps LBT where so much rain fell recently. Showers streaming onshore to increase in coverage predawn but only tend to MVFR with any IFR dips too brief to warrant being in TAFs. Dry slot sweeps west to east across the area this afternoon and clears things out. Slight chance of very minor visibility restrictions returning Friday night. EXTENDED OUTLOOK...Primarily VFR. Isolated to scattered afternoon showers through much the period, although limited in strength and coverage due to dry air aloft. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 330 AM Friday...Sfc cold front across the inland Carolinas will push to the coast late tonight and likely stall along the immediate coast or just offshore Sat and subsequent periods. This will be the dividing line for pcpn coverage. East of the front pcpn will be more numerous and potent, and west of the front isolated in coverage. Looking at S winds at 10 to 15 kt today and SW 10 to 15 kt tonight, with speeds lower within the actual frontal zone. Significant seas will be a healthy 3 to possibly 4 ft, and comprised of mainly wind driven waves at 4 to 6 seconds. An underlying 1 foot ESE ground swell at 10-11 second periods will be present. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 345 PM Thursday...A cold front will be west of the waters Friday before wavering across or potentially still just inland on Saturday. This creates predominantly S/SW winds of 10-15 kts on Friday, backing to the SE around 10 kts on Saturday, again dependent on where the front stalls. A period of variable winds is possible late Friday into Saturday as the front drifts into the vicinity, but speeds will be light during that time. Seas will hover around 3 ft both Friday and Saturday with a low amplitude 9-10 sec SE swell and 2-3 ft 5 sec southerly wind wave comprising the spectrum. LONG TERM/MONDAY THROUGH TUESDAY/... As of 3 AM Friday...A northeasterly wind wave and increasing ESE ground swell energy to cause a gradual rise in seas over the long term. Tough to say how high the wind speed and resulting short period seas get though as most model guidance is seemingly too fast with Matthew. Winds may end up being reduced this period assuming the slow movement of the currently favored EC model comes to pass. The aforementioned swell energy is less related to Matthew and more energy from the long fetch developing. Any Matthew swells (and there will be some!) may be slated for just beyond the long term. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...MBB NEAR TERM...DCH SHORT TERM...MJC LONG TERM...MBB AVIATION...MBB

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