Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 251741 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 141 PM EDT Sun Sep 25 2016 .SYNOPSIS... A cold front will stall across South Carolina tonight before returning north Monday. A stronger cold front will move across the Carolinas Wednesday or Thursday. Behind this next front, drier and cooler weather will arrive on northerly winds. && .NEAR TERM /THROUGH TONIGHT/... As of 1230 PM Sunday...Enough sun has finally made it through the low clouds across NE North Carolina and coastal South Carolina to fragment them and lift cloud bases substantially. The latest HRRR still isn`t excited about rainfall potential, however the new 12z synoptic models (GFS and NAM) still show that potential later this afternoon, especially from just west of Wilmington to near Conway, a short distance behind the frontal position. Minor tweaks have been made to forecast highs. Discussion from 945 AM follows... The cold front slipped through Wilmington before sunrise but is decelerating as it pushes farther southwestward. Northeasterly winds both ahead and behind the front are making it tough to find the exact frontal location, but it appears at 9 AM to run from Bennettsville and Dillon to Whiteville and Southport. Overnight radiational cooling out ahead of the front produced widespread fog, some quite dense, which is slowly burning off across coastal South Carolina up through Marion into Lumberton. Post-frontal low stratus has built into the Maxton- Lumberton-Elizabethtown area but has remained north of Wilmington. With the front almost stalling during peak diurnal heating this afternoon, look for scattered showers and thunderstorms to develop near or behind the front. That`s not normally how fronts work in this part of the country, but in this case the front is bringing in deeper moisture from the Atlantic, making the best precip chances behind the front. SBCAPE rises to 500-1000 J/kg and convective capping falls to 0-10 J/kg. The latest several HRRR runs aren`t all that impressed with shower chances this afternoon, but I am not going to remove the 20-30 PoPs in the forecast. Cell motion should be very slow from north to south. Highs today should range from the upper 80s in the Pee Dee Region (a 90-degree reading is even possible west of Florence) down to the lower 80s on the NC beaches. The 06z NAM looks to have a better synoptic handle on the frontal position and temperatures than the GFS. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure across New England will drift offshore and this will allow the cold front to push back N of the area during the day with surface winds turning onshore and eventually to the SE Mon afternoon and eve. A subtle mid-level shortwave will sneak up the coast late in the day Mon and Mon night. A vigorous trough carving out across middle America is expected to drive a cold front into and eventually through the eastern Carolinas Tue night or Wed. Moisture will increase steadily during Tue and Tue eve and then begin to drop off sharply with frontal passage overnight, lastly along the coast Wed. Will show convection through the period, but include the highest probability Tue afternoon and night. Highs will be about normal, lower 80s. Lows will be in the upper 60s to lower 70s Mon night and then cooling in the wake of the cold front to mid and upper 60s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 300 AM Sunday...Deep upper low will evolve across the Great Lakes and then sink slowly SE through late week before ejecting into Canada during the wknd. This will drive a cold front across the Carolinas on Wednesday, but its overall progression is a low confidence forecast due to model uncertainties into the evolution of the aforementioned upper low. ECM is deeper and stronger with this upper low, cutting it off entirely from the mean flow into next wknd. The CMC is the fast solution with short cutoff followed by rapid progression into the westerlies by late week. The GFS is a decent compromise, although its ensembles show a very large spread by D6. The biggest difference to the sensible weather from these solutions revolves around precip potential, as temperatures will likely be seasonable or slightly below regardless of which outcome is correct. Will favor the GFS attm which is supported by WPC, which suggests the front will push offshore as the upper low begins to move NE Thursday, with cool high pressure building down the coast thereafter. Temperatures Wed/Thu will likely be around seasonable norms or slightly above, but clouds and showers will be likely as the front drifts towards, and then off, the SE coast. As the high builds south late week and into Saturday, temps will cool to below normal with mins potentially dropping to 60 or below, especially inland, by the end of the period. If the ECM solution ends up being correct, temperatures will still follow this trend, but both Friday and Saturday could also feature periods of showers instead of the drier forecast currently being shown. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 17Z...Favored a blend of the models for this period with more confidence in the NAM and GFS then the ECMWF due to the handling of the H5 low across the nrn portion of the country during the next few days. Cold front south of KILM and KLBT at this time and right near KCRE/KMYR/KFLO. Predominately northeast flow and MVFR conditions are expected with mention of vcsh along the coastal terminals but will leave out mention inland. HRRR a bit overdone with the pcpn potential across the region but as mentioned in the near term forecast best chances for pops are just behind the front so that is enough reason for the vcsh. BUFKIT seems to agree with this scenario as well with pcpn ending around 00z across the coastal terminals. Moderate confidence in MVFR due to ceilings during the overnight period with improvement to vfr after daybreak. Winds will stay up along the coast but I will lower across KLBT and KFLO overnight. EXTENDED OUTLOOK...Chance for SHRA/TSRA each day through Wed. Otherwise expect VFR. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 1230 PM Sunday...The front is still making some progresses southward down the SC coastline, with breezy NE winds in its wake. Seas are still building in-line with our previous forecast and no changes are necessary with this early-afternoon near term update. Discussion from 945 AM follows... A cold front has pushed as far south as Cape Fear this morning, and should crawl southwestward along the South Carolina coast this afternoon. Northeasterly winds are in place both ahead of and behind the front, making wind speed and air pressure the best determining factors for locating the actual front. Northeast winds should increase to a solid 15 knots with gusts to 20 knots today, strongest in the Cape Fear vicinity. Seas already as high as 3.5 to 4 feet north of Cape Fear should build to 4-5 feet near and north of Cape Fear this afternoon, 3-4 feet along the SC coast later this afternoon. Isolated showers or t-storms could develop this afternoon in the Cape Fear to Myrtle Beach vicinity, but most should remain inland. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 300 AM Sunday...High pressure across New England will move offshore and this will allow winds to shift from NE and ENE Mon morning to E Mon afternoon and to SE Mon night. As a cold front approaches the waters, SE winds Tue will become S and SW Tue night. If the front does not slow down, winds may shift to the N as early as the wee hours of Wed morning. The highest winds this period will be Mon and Mon eve, up to 10 to 15 kt. Seas of 3 to 4 ft Mon and Mon night will subside to 2 to 3 ft Tue and Tue night. LONG TERM/WEDNESDAY THROUGH THURSDAY/... As of 300 AM Sunday...Some uncertainty exists in the extended with respect to the timing of a cold front moving across the waters, but attm it appears the front will stall over the waters Wednesday and then shift well offshore during Thursday. This leaves a period of highly variable winds on Wednesday with speeds of 5-10 kts, before the front moves away Thursday followed by N to NE winds of 10-15 kts. Seas Wed and most of Thu will be 2-3 ft with residual 11-12 sec swell remaining in the spectrum combined with low-amplitude wind waves. Late in the period a northerly 4-5 sec wave will amplify, and seas may build towards 3-4 ft late Thursday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS... NEAR TERM...TRA SHORT TERM...RJD LONG TERM...JDW AVIATION...MAC MARINE... is the U.S. government's official web portal to all federal, state and local government web resources and services.