Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231546 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 605 AM EST Thu Nov 23 2017 .SYNOPSIS... High pressure will build over the Carolinas through today as low pressure begins to move slowly up from the Gulf of Mexico spreading clouds and some rain over the Southeast. The low may track close enough to the Carolina coast to produce some intermittent rain mainly along the immediate coast late today into Friday before departing on Saturday. A dry cold front will move through Saturday night followed by Canadian high pressure through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM Thursday...High clouds were streaming northward in SW flow on the front end of mid to upper trough. This trough will dig southward today into the Gulf before pushing eastward by tonight. Shortwave energy rotating around the main trough will produce waves of low pressure which will track northward up from the eastern Gulf to just off the Southeast coast through tonight. The best lift associated with this low pressure will remain mainly off the coast, but a low end chc of pcp will exist into SC and mainly along the coast into NC later today into tonight. For now will keep any measurable pcp out of the forecast. A tight gradient will exist between cooler and drier high pressure to the west and low pressure to the east. Pcp water values will remain under a half inch from I-95 and west and up to 1.6 inches off the coast. Dewpoint temps were down below 30 inland and up closer to 40 along the immediate coast this morning and will remain low through the period. Temps will only reach into the 50s today in cool northerly flow. The mid to upper trough will nudge the greatest moisture east through tonight. This will clear out most of the clouds over western portion of forecast area while clouds will remain along the coast through tonight. This will produce another large spread in overnight lows tonight with mid 30s inland to mid 40s along the coast.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...Finally, models are all trending together in keeping the main area of pcpn just off the ILM CWA Coasts early Fri before, finally progressing this pcpn well offshore during daytime Friday. The drying trend amongst the models are likely mainly due to a northern stream mid-level s/w trof that dives SE to the Gulf Coast States during Thu, then progressing eastward Thu night thru Friday. This upper s/w trof remains positively tilted and much less amplified than what prior models forecast several days ago up until yesterday. With a flattened mid-level s/w trof, the easterly component in the wind fields aloft will push the sfc low and ultimately the baroclinic zone it`s feeding off of, to well offshore from the Carolina Coasts by late Friday. As mentioned in prior fcsts, a decent moisture and POP gradient will exist late Thu thru Friday before finally shifting well offshore by late Friday. With that said, have kept POPs in the low chance for light rain across the coastal counties early Fri. The tight moisture gradient will also result in sky conditions going from cloudy to clear as the back edge of this cloud field pushes east. Weak sfc high will prevail late fri thru daytime Saturday. Moisture profiles across various ILM CWA locations indicate a dry mid and upper levels to exist Fri night thru Sat resulting in mainly clear Fri night and mostly sunny for Sat. For late Sat thru Sat night, a vigorous sfc cold front will drop southeast and across the FA Sat evening and off the Carolina coasts and offshore after midnight Sun. A potent and southeast moving mid-level s/w trof will help amplify the longwave upper trof across the Eastern U.S. as well as accelerating the sfc cold front across the FA. Moisture will remain starved for this cold front, with enough for cloudiness but not deep enough for any pcpn. This a result of the downslope wind field within the atm column that will tend to scour out moisture. With that said, did not include POPs and have kept a partly to variably cloudy sky conditions Sat night. The temp fcst during this 2 day period will be unremarkable, meaning expect max/min temps near their respective climo norms. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday...Primary weather caption for this time frame remains `seasonably cool, and dry` as a series of upper troughs progressively traverse the coast, the strongest brings cold air advection Sunday. The coolest portion of this time period looks to be daybreak Monday, when high pressure becomes centered over the inland Carolinas under clear skies at first light. The breeziest part of the forecast will be Sunday as high pressure builds in from the west. Late in the extended period for days 6/7, a return and moisture flow slated, as a moderately strong upper trough digs into the central MS Valley, hence, a warm air advection trend appears on tap for next Tue/Wed, with a slight chance of rain as a warm front arrives from the south in the return flow. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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As of 12Z...High pressure to our west will give us fairly decent aviation weather today. A weak wave will ride up the eastern seaboard this evening. Clouds will lower to at least mid cloud. There is still some uncertainty as to how far inland the moisture will get. Looks like the worst case scenario would be some light rain at the coastal terminals with a VFR ceiling around 4k feet. Will fine tune overnight forecast with the next model run. Extended Outlook...Possible showers along the coast on Friday, and Saturday night, otherwise VFR.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 300 AM Thursday...Northerly surge through this morning will produce marginal SCA conditions. N-NE winds up to 20 kts with higher gusts will produce seas up over 6 ft with WNA model showing highest within the first few hours after daybreak today. The high will shift east with winds veering to northeast through today. Northeast winds around 20 kt continue into this morning before surge eases and the gradient relaxes. Winds will diminish to 15 kt by midday, but should see winds increase slightly tonight as low pressure moves up from the south and gradient tightens again. Seas will remain 4 to 6 ft through this morning before starting to decrease as wind speeds drop off. Seas should remain 3 to 5 ft through tonight but may be on the high end overnight into early Fri. SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... As of 300 AM Thursday...SCA will likely be ongoing at the start of this period due to a tightened sfc pg as the sfc low just offshore pulls away from the Carolina Coasts. Weak sfc high and it`s elongated center, will push across the Eastern Carolinas and off the coast Fri night thru midday Saturday. NE 15 to 20 g25 kt winds early Fri will back to the North thru Northwest Fri aftn thru early Sat with wind speeds subsiding to 10 to 15 kt as the sfc pg relaxes. The sfc pg will re-tighten-some Sat aftn and evening due to the approach and passage of the next cold front. This CFP not as dramatic as previous ones but nevertheless westerly winds to increase to around 15 kt ahead of the front becoming northerly 10 to 20 kt with few gusts up to 25 kt. Significant seas will have peaked at the start of this period followed by a general subsiding trend Fri aftn thru midday Sat before bouncing back into a slight uptrend Sat aftn and night. With wind directions generally offshore, there will be a limited fetch for which seas to build upon during Sat aftn and night. At best, a short term SCEC remains possible for late Sat aftn and night. LONG TERM /SUNDAY THROUGH MONDAY/... As of 300 PM Wednesday...High pressure will build into the area waters behind cold front through the day Sunday. The breeziest day and highest seas will be Sunday as North winds up to 20 KT prevail, with a few higher gusts. Wave guidance showing 4-5 feet offshore Sun, thus a precautionary headline may be needed. As the high pressure center nears, N winds will veer to NE and weaken on Monday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Small Craft Advisory until 3 PM EST this afternoon for AMZ250- 252-254-256.
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&& $$ NEAR TERM...RGZ SHORT TERM...DCH LONG TERM...MJC AVIATION...43

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