Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 171946 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 346 PM EDT Tue Oct 17 2017 .SYNOPSIS... Canadian high pressure building into the Mid-Atlantic states today will bring several days of cool, dry weather to the Carolinas. Temperatures should begin to warm up this weekend as the high moves off the coast. && .NEAR TERM /THROUGH WEDNESDAY/...
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As of 300 PM Tuesday...Surface high north-northwest of the region will maintain dry and cool conditions through the period. In the mid- levels a 5h trough will move off the coast this evening with a weak shortwave ridge trying to build north. Cloud cover along the coast this afternoon, a result of increased moisture above 400mb, will gradually shift offshore this evening leaving clear skies overnight. Deep northerly flow aloft will contribute to an abundance of dry air, as will subsidence behind the exiting 5h trough and along the top of the marginal 5h ridge. Low level dry air and boundary layer winds around 15kt should keep surface mixed enough to prevent any fog development. Mixing will also limit the effectiveness of radiational cooling, although overnight lows will end up around 5 degrees below climo. Inland cold spots will be right around 40 with locations along the coast near 50. Slight increase in thickness Wed (both low level and 1000-500mb)as the air mass starts to modify, mainly due to sunny to mostly sunny skies, will result in highs topping out right around climo. Low level convergence off the coast may lead to some marine clouds and showers but do not see much cloud moving onshore, let alone any precipitation.
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
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As of 300 PM Tuesday...High pressure becomes elongated from the southern Appalachians northeast into the Atlantic waters Wed eve. This will allow for a greater on shore component to the low level winds which should give a push to some of the maritime moisture from the coastal waters associated with a bit of shortwave energy riding by. This enhanced low level moisture should move down from the NE Wed eve brushing the coast. Moisture profiles show a very dry column above 5k ft but a decent shallow layer below with mainly some strato cu clouds expected overnight Wed into early Thurs. By Thurs aftn, the high pressure becomes centered over the southern Appalachians allowing for a deeper northerly flow, cutting off the Atlantic moisture and providing a reinforcing push of dry air. Another minor shortwave passes by Thurs aftn but the column remains too dry to produce anything more than a few clouds. Pcp water up near an inch along the coast Wed night will be down to a half inch by Thurs aftn. Inland remains near a half inch through the period. Overall, aside from some passing clouds, expect dry and seasonable weather through the period. Better radiational cooling Thurs night with lighter winds and mainly clear skies expected but basically a gradual warming trend should keep overnight temps roughly the same both nights...within a few degrees on either side of 50. The high temp on Thurs should be nearing 80 most places.
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&& .LONG TERM /FRIDAY THROUGH TUESDAY/...
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As of 300 PM Tuesday...It will remain high and dry into Sunday as high pressure remains in control of area weather. An approaching cold front and return flow around the high will bring increasing clouds Sunday and Sunday night with a small chance of showers. Chances for showers will continue Monday and Tuesday as the front moves into and through the area. Max temperatures Friday through Monday will be in the upper 70s to around 80 and in the mid 70s Tuesday. Minimums will moderate from the low to mid 50s Friday morning to the low to mid 60s Monday and Tuesday morning.
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&& .AVIATION /18Z TUESDAY THROUGH SUNDAY/... As of 18Z...High pressure will persist across the TAF sites for the next 18 hours with VFR/no cigs. Winds will be 10-50 degrees at 10-15 kt with gusts to around 20 kt, decreasing to less than 6 kt by late afternoon. Time height progs low level moisture will increase at coastal terminals below a substance inversion after 12z. Attm expect sct stratocumulus at best coastal terminals late morning. Extended Outlook...Possible MVFR cigs Thurs AM. Otherwise VFR. && .MARINE...
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NEAR TERM /THROUGH WEDNESDAY/... As of 300 PM Tuesday...Northeast flow of 20 to 25 kt this afternoon will decrease to around 20 kt this evening and overnight as cold surge relaxes and gradient weakens slightly. Although northeast winds will drop below 25 kt by evening, seas will stay above 6 ft well into Wed, a result of a prolonged period of strong northeast flow. The exception will be in AMZ254 where the bulk of the north- northeast winds/swell have been sheltered by land. Based on latest guidance the inherited SCA end time of 9 PM EDT seems reasonable. It also seems likely that the SCA will be replaced by a SCEC for the overnight period. Seas will be under 6 ft but 4 to 5 ft with wave periods 5 sec or less seem likely within the zone. It is also possible that the end time of the SCA may need to be extended beyond 6 PM EDT Wed. However have low confidence in this for now and do not plan any adjustments to the headlines. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...High pressure will be more elongated from SW to NE north of the area which will produce a slightly more easterly component to the wind through Wed night. This NE push of winds up to 20 kts will continue to produce seas up near or slightly above SCA thresholds, near 6 ft, through Wed evening. WNA model shows a decrease in seas to below SCA criteria after midnight as gradient relaxes slowly into Thurs. Also, the winds will become more northerly in direction through Thurs which should help keep strongest winds off shore. Seas 4 to 6 ft initially will be down to 3 to 5 ft by Thurs aftn and 2 to 4 ft by Thurs night. LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Northeast winds of 10 to 15 KT Friday will gradually become easterly by Sunday morning then southeast by Sunday night. Seas of 2 to 4 FT Friday will diminish to 2 to 3 FT Saturday then increase to 3 to 5 FT by Sunday evening.
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&& .TIDES/COASTAL FLOODING...
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As of 300 PM Tuesday...Astronomical tides are increasing as we approach a new moon. This coupled with strong NE winds, may breach minor coastal flooding thresholds at Wrightsville Beach beginning today, and advisories may be needed along portions of the coast the next several days. The same will be true of the lower Cape Fear including the downtown Wilmington area.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...Beach Hazards Statement until 9 PM EDT this evening for SCZ054- 056. NC...Beach Hazards Statement until 9 PM EDT this evening for NCZ106- 108. MARINE...Small Craft Advisory until 6 PM EDT Wednesday for AMZ250-252- 256. Small Craft Advisory until 9 PM EDT this evening for AMZ254. && $$ NEAR TERM...III SHORT TERM...RGZ LONG TERM...RAN AVIATION...MRR

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