Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 200738 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 338 AM EDT Mon Aug 20 2018 .SYNOPSIS... High pressure offshore will maintain warm and humid weather today, with isolated showers and thunderstorms. Rain chances will increase ahead of a cold front Tuesday into Wednesday. An early hint of fall will arrive late week, as Canadian high pressure drops in behind the front, bringing drying and slight cooling, Friday into the early weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 338 AM Monday...Convection and coverage thereof continues to underperform with the synoptic scenario. The axis of concentrated activity this morning is to our north associated with a couple of shortwaves embedded in the generally westerly flow aloft. For the next few hours I have dramatically decreased pops as there will inevitably be some NVA in the wake of the activity. As for later today, somewhat of a repeat of the past couple of days with an agonizing struggle for convection. The GFS paints a wide swath of showers later this morning but this may be more of a stratus layer that persisted inland for a while Sunday. The GFS has been way to aggressive with pops/qpf anyhow. Overall still have slight to low chance pops along the coast to chance northern and inland areas. Some indication of diurnal activity early Tuesday but based on the past couple of nights and really all periods confidence is low. Essentially no change from previous days and nights for the thermal forecast. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 338 AM Monday...Warm air advection encompasses nearly all this time period, with a frontal passage prior to daybreak Thursday, and GFS/ECMWF surface agreement on timing, with cool air advection poised to filter in Thursday. Precipitable water analysis shows a peak in vapor content late Tuesday before a decreasing trend, as the river of high PWATs edges offshore. As such, column drying will already be underway well before frontal passage, with drying down to 700 mb Wednesday. A short wave and jet energy to the north late Wednesday, will sustain shower chances into evening, driving frontal passage through the area prior to sunrise Thursday, and sharp drying commencing, and Td values lowering. Increasing atmospheric wind shear will raise the odds a bit of a severe TSTM wind gust, mainly Tuesday afternoon to Wednesday morning. The forward speed of the storms from the WSW to ENE could drop strong wind, MLCAPE/MUCAPE progged around 2000 j/Kg and partial sunshine will create locally higher SBCAPE and spur differential heating Tuesday afternoon. The SPC has place portions of the region in `marginal` risk, favored to NC moreso than SC. QPF values not that high Tue/Wed as convection is apt to be in hit and miss coverage, generally 0.25" SC and 0.50" NC, `basin average` rainfall. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 3 PM Sunday...Mid-level pattern will be marked by 5h trough through Fri before weak 5h ridge expands east over the area. Lack of deep moisture will limit precip chances somewhat during the period, the best chances likely being Wed as the arriving trough pushes a cold front into the area. Surface high building in ensures the front and deeper moisture shift a little farther offshore into the weekend. At this point uncertainty creeps in concerning how quickly a weak coastal trough develops and then moves onshore as the high to the north shifts east. Will continue to carry chance pop Wed with chance to likely pop Wed night. Once the front is through, confidence in the forecast decrease and will carry slight chance to chance pop for the remainder of the period. Given the lack widespread deep moisture think diurnal activity will be limited along the sea breeze and any lingering boundaries. Temperatures start off above climo but following the passage of the cold front later Wed temps drop below climo for Thu through Sun. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... As of 06Z...Once again similar conditions expected regarding the evolution of showers and thunderstorms for the mostly daytime period. Expect mainly VFR conditions as the coverage should once again be limited. As for the next few hours, fairly strong signals that LBT and FLO will see at least a brief period of IFR fog and or stratus and used tempo groups to address. Extended Outlook...Scattered showers and thunderstorms each afternoon and evening, accompanied by brief MVFR conditions. Cold front late in the period Thursday may cross all terminals of SE NC and NE SC, bringing a surface wind- shift. && .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 338 AM Monday...Expect southwest winds through the period as the synoptic pattern remains all but unchanged through early Tuesday. Wind speeds will be 10-15 knots with some intervals of 15-20 knots which will mostly occur during the overnight hours. Significant seas will remain generally consistent as well with a range of 2-4 feet. Even with the higher winds both currently and again Tuesday morning the need for a SCEC headline is not anticipated. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 338 AM Monday...Not ideal marine conditions, as SW winds this period begin to pick ahead of an approaching cold front set to cross the coast around daybreak Thursday. Tuesday afternoon through early Wednesday, 15-20 kt winds and a few gusts to 25 kt likely. Thus a brief SCA cannot be ruled out this period ahead of the cold front. TSTMS will be moving to the ENE-NE and radar updates are recommended before venturing offshore this period. The bulk of wave energy is wind driven this period with dominant wave periods around 5 seconds. Winds shifting to N-NNE after sunrise Thursday. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 3 PM Sunday...Pinched gradient Thu morning leads to slightly increased northeast flow, an event that will be repeated late Thu night as secondary northeast surge sets up. Second round Thu night will be stronger with solid 15 kt winds possible. Seas 3 to 5 ft at the start of the period gradually fall to 3 to 4 ft late Wed and Wed night and 2 to 3 ft Thu and Fri. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...8 NEAR TERM...SHK SHORT TERM...MJC LONG TERM...III AVIATION...SHK

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