Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 190008 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 808 PM EDT Tue Apr 18 2017 .SYNOPSIS...
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A cold front stalled over South Carolina will lift back north as a warm front Wednesday into Thursday. The Bermuda High will expand west over the region Thursday through Saturday. Another cold front will move through Sunday night with high pressure building in behind it into early next week.
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&& .NEAR TERM /THROUGH WEDNESDAY/...
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As of 9 PM Tuesday...Long-lived convection over the SC portion of our forecast area finally on its last legs, with no more lightning in evidence and a transition to a remnant stratiform rain shield ongoing. Will make some slight adjustments to pop and weather grids, otherwise no changes needed to the forecast. Previous discussion from this afternoon follows: High pressure will ridge in behind cold front draped from NE SC southwestward into SC. A moisture rich air mass but more stable air mass behind the front over NC was producing low clouds and spotty light rain in cooler northerly sfc flow behind the front. Ahead of the front the winds were still S to SW with some mid clouds mixing with the sunshine. Temps to the north were in the mid 60s while to the south the temps were into the 70s. The heating to the south was producing more unstable conditions this afternoon and therefore included some thunderstorms into northeast SC into early this eve. This activity will be focused in more unstable air mas to the south of the front and will be aided by convergence along sea breeze boundary just inland of SC coast and by differential heating boundaries. Temps to the north of the front were struggling to reach into the 70s while temps to the south reached 75 to 80. Models showing some decent isentropic lift over inland Carolinas, mainly NC, tonight as southerly low level winds ride over the shallow cool air behind the cold front. The lift will be enhanced as a shortwave makes its way into the Carolinas from the west. It looks like this pcp will remain mainly west of local forecast area, but soundings and moisture profiles show low clouds and fog a possibility. Also expect some pcp possible as lingering boundary/trough over SC coast produces some pcp as well. This trough/weak low will push inland on Wed as high pressure remains wedged inland. Expect shwrs and iso thunderstorms in convergence along this trough/lingering frontal boundary as some shortwave energy rides through. May end up being focused closer to the I-95 corridor Wed afternoon. Lows tonight should be around 60, influenced by the lingering clouds and moisture. Wed highs will reach the 70s most places with some breaks of sun.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Warm front will lift slowly north across the area during Thursday as surface high pressure settles off the southeast coast. This will pump warm air into the region and highs on Thursday will climb into the low 80s, mid 80s inland, after a mild Wednesday night with lows around 60. As this warm front lifts north, surface convergence along it will combine with a westward propagating sea breeze to produce isolated to scattered convection on Thursday. The high- res guidance is less aggressive with areal coverage of showers and storms, likely due dry W/NW flow aloft, and the best chance for tstms will be along the sea breeze as it penetrates well inland thanks to combined synoptic SE flow. Most of the convection is expected to be showers, but isolated tstms are possible as MLCape increases to 500-800 J/kg despite relatively weak ML lapse rates. Very warm temperatures are forecast Thursday as warm southerly flow persists, and minimums will only drop into the mid 60s, a full 10+ degrees above climo. One other thing to note is a weak surface trough/low that may form along the warm front and just offshore. This feature is likely to be weak, but could provide slightly more lift and moisture that QPF along the coast, especially in any tstms, would be enhanced. Still do not expected widespread or heavy convection, but WPC has a focused area of heavier rainfall, albeit still only around 0.25 inches, along the Cape Fear coast. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...A streak of very warm weather is expected Friday and Saturday before a significant rain/thunderstorm event accompanies a cold front early next week. A low amplitude upper ridge across the Southeast will support surface high pressure out near Bermuda on Friday and Saturday. Southwesterly low-level flow around this high should provide two warm days with highs easily reaching the upper 80s on Friday. Earlier models had suggested a backdoor cold front may slip southward into the area, but this appears to be a much lesser possibility now. I have increased forecast highs and lows Friday through Saturday by as much as 6 degrees in spots, and feel that I still may be too cool, especially inland on Saturday. Capping aloft with the ridge should keep diurnal thunderstorm activity in the isolated range, mainly inland of each day`s seabreeze front. Our weather pattern changes abruptly by Sunday as an impressive upper level system (especially for late April) dives into the southeastern quarter of the nation. Timing differences between the GFS and ECMWF has narrowed quite a bit with this morning`s 12z model run, and confidence is growing that a wave of thunderstorms will progress from west to east across the area late Sunday ahead of the surface cold front. A non-supercell severe risk may very well develop with this system as models are showing rather strong but unidirectional winds aloft coupled with a favorably positioned jet stream along the Mid-Atlantic and New England coast. As the mid and upper level system slows and almost cuts off along the GA/SC coast on Monday, steadier rains could linger through Monday and perhaps into Monday night along the coast. This is excellent news for especially South Carolina as "abnormally dry" and "moderate drought" designations are expanding on the latest U.S. Drought Monitor summary. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 00Z...Good confidence cigs will hover right around 3000 ft through at least the initial 12 hours of the TAF valid period for all sites, with lesser confidence thereafter. So, it looks like all sites will be in and out of MVFR criteria through the period. Good confidence that convection will re-initiate Wednesday afternoon area-wide. Extended outlook...MVFR/IFR conditions possible in showers and TSTMS Saturday through Sunday night.
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&& .MARINE...
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NEAR TERM /THROUGH WEDNESDAY/... As of 9 PM Tuesday...Latest obs show NE winds of 10 to 15 kts with seas of 3 to 4 ft. This fits in well with the latest forecast so no changes are expected with the latest update. Previous discussion follows: A rather weak cold front is dropping slowly south across the waters, but will stall out near or just south over SC waters later today. Winds will be N to NE north of the boundary and S to SW to the south of the front. Most of the coastal waters will see a northerly component to the winds develop through today with the exception of AMZ256 where the front may stall producing more variable winds. Winds will be generally light but will increase and become gusty behind the front into this evening but will diminish again into Wed morning. The increase in winds with a greater on shore component will push seas up from less than 3 ft up to 3 to 5 ft overnight into Wed morning. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...A warm front to the south will lift slowly north across the waters late Wednesday night into Thursday. This persists a weak gradient, and winds will be light and variable Wednesday night before developing a SW primary direction Thursday behind the warm front. Wind speeds increase behind the front, becoming SW at 10-15 kts Thursday and Thursday night. There is also likely to be a sea breeze in the near shore waters Thursday aftn, with winds backing more to the south along with a more rapid climb in speed. A variety of wave groups will exist Wed night, and seas will remain low amplitude around 1-3 ft. On Thursday, a SW wind wave will amplify and combine with long period easterly swell from a non tropical cyclone in the middle Atlantic, to drive seas up to 3-4 ft Thursday night. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...High pressure out near Bermuda will control our area`s weather through the end of the week, maintaining south- southwesterly winds and generally dry conditions. Compared to models a day or two ago, the high is now expected to be stronger and should deflect a backdoor cold front that was earlier believed to make it this far south. Wind speeds should average 15 knots on Friday and 10- 15 knots on Saturday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...REK NEAR TERM...REK/RGZ SHORT TERM...JDW LONG TERM...TRA AVIATION...REK MARINE...REK/TRA/RGZ

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