Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231149 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 749 AM EDT Wed May 23 2018 .SYNOPSIS... A weak cold front approaching from the north will produce a greater coverage of showers and thunderstorms today and on Thursday. The front will dissipate by Friday. Low pressure developing across the Gulf of Mexico will bring tropical moisture northward and help fuel a higher probability of showers and thunderstorms with heavy rain across the eastern Carolinas Sunday and into early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...Expect an active day regarding showers and thunderstorms as gradual height falls, a very moist column and a cold front slipping south work in tandem. I am liking the guidance trend of showing mostly sea breeze/air mass showers and isolated thunder later this morning and early afternoon. More organized activity appears to develop later in the afternoon from north to south with the added assist from the front or more likely an outflow boundary emanating from early convection to the north with the front. We are still advertising likely pops from late morning on. Regarding severe potential, plenty of CAPE but shear is a little light. Flooding could pose a threat especially along the coast where plenty of rain has fallen in the past few days and somewhat sluggish storm motions. Activity could persist through the overnight hours, but should trend downward somewhat. The MET guidance has been spectacular with temperatures and opted for these numbers almost verbatim. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A weak cold front will be in close proximity Thu and should become ill-defined to our S by Fri. An area of high pressure will briefly nose into the area from the N, moving progressively offshore late in the period. An upper trough will lift out Thu followed by a building ridge Fri and Fri night. Precipitable water values will only drop very modestly as we move from Thu into Fri with slightly more drying noted later Fri and Fri night. Given a front will be slowly dissolving across the area as it struggles to advance southward, it will be difficult to refrain from including at least some risk for showers and thunderstorms. Moisture profiles show the moisture depth decreasing, especially later in the forecast period. Will show chance to likely POPS Thu and this activity is expected to lessen significantly or end with nightfall. Then on Fri, will include mainly slight chance/small chance for convection, mainly across South Carolina. Expect the convection Fri to be mainly diurnally driven. High temps will be near to slightly above normal for late May. The beaches will be coolest as onshore flow prevents them from rising above the upper 70s and lower 80s. Lows will be in the mid 60s to lower 70s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM Tuesday...A baggy upper level trough across the lower Mississippi Valley and Gulf of Mexico will become better defined Saturday and Sunday. Upper ridges building across the Pacific coast of Mexico and out over the western Atlantic between the Bahamas and Bermuda will help to spin this feature up. A surge of Caribbean moisture very similar to what we saw last weekend will be drawn northward in the deep southerly flow between this upper trough and the offshore ridge, and this could lead to another significant rainfall event Sunday into Monday. The latest WPC QPF outlook for just Sunday and Monday is around 1.5 inches across our area, with forecast 7-day totals of 2-3 inches. Latest models show there will probably be some sort of low pressure development across the Gulf of Mexico late this week, but FSU cyclone phase diagrams show only the Canadian developing a significant warm core aloft. The 12z ECMWF (not currently part of the FSU website) shows the cyclone keeping a pronounced gradient in 1000-500 mb thickness above the surface low, implying subtropical characteristics at best. The GFS is the farthest east with its low pressure development across Florida on Sunday, while other guidance is westward. While not ruling out anything just yet, it`s expected the low will remain too far west for any direct impacts on the Carolinas, but enhanced southerly flow should help enhance our rainfall potential Sunday and Monday when my highest rainfall chances (50-70 percent) are currently forecast. A warm day Saturday when there will be more sunshine and lower shower chances. Highs should reach the mid to upper 80s inland, several degrees cooler near the coast. Temperatures should top out in the lower 80s Sunday, and lower to mid 80s Monday and Tuesday. Lows in the upper 60s to lower 70s through the period are evidence of the tropical airmass we`ll have in place. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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As of 12Z...Fog/IFR/MVFR cigs will improve to VFR 12-14Z, with only a brief MVFR cig possible the remainder of the morning. An upper impulse will move across the terminals today. Mostly showers, with possibly an isolated thunderstorm, is expected mid-morning to mid afternoon at the inland terminals, and in the afternoon at the coastal terminals. Will maintain VFR in TAFs attm although tempo periods of MVFR possible with the showers. Since thunderstorms will be isolated any IFR will be very very brief. This evening models showing convection ahead of a cold front moving south and affecting the KILM/KLBT terminals around 04Z and the southern terminals 06Z. Confidence is higher this will be the better shot at tempo thunderstorms and sub-VFR. After activity dissipates there is moderate confidence MVFR/IFR with BR/stratus will develop. Confidence of timing/duration is low. Low cigs could persist through mid-morning with N-NE winds Thursday morning. Extended Outlook...Potential for MVFR/tempo IFR/Thunderstorms southwest terminals Thu aftn/evng. will increase late Wed/Thur as a cold front drops across the area and again during the weekend as tropical moisture returns.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...Southwest winds of 10-15 knots will be in place for most of the day across the waters. Some increase in speeds to 15-20 knots is expected this evening with enhancement of low level jetting especially across the southern waters. A west to even northwest flow develops late tonight into early Thursday morning as a front or arguably outflow pushes across the waters. Significant seas remain in a 2-4 foot range. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...A weak cold front will be in close proximity Thu and should become ill-defined to our S by Fri. An area of high pressure will briefly nose into the area from the N, moving progressively offshore late in the period. The wind direction Thu will shift from W and NW early to easterly. Easterly winds will then hold into Fri before veering to SE Fri afternoon and S fri night. Wind speeds will be no higher than around 10 kt through the period. Seas will be 2 to 3 ft. A SE swell should gradually build across the waters late in the period. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Bermuda high pressure will remain well off the Southeast coast this weekend. By itself it would provide a gentle southerly wind and typical summertime weather. However models over the past few days have been showing the potential for a tropical or subtropical cyclone to develop across the Gulf of Mexico by Saturday. The GFS is the farthest east of any of the models with its latest run showing a low reaching Florida on Sunday, while the ECMWF and Canadian are farther west. While it`s too early to completely rule out impacts, our latest forecast has south winds increasing to around 15 kt Sunday, with a lengthening fetch of stronger winds extending down into the Bahamas. This could build seas up toward 6 feet, assuming our wind forecast is correct. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ NEAR TERM...SHK SHORT TERM...RJD LONG TERM...TRA AVIATION...MRR

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