Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 231550 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 1050 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 10 AM Thursday...Shortwave moving up the east side of the 5h trough, accompanied by deeper moisture and a weak surface wave, continues to increase cloud cover across the area. Rainfall has been slowly but steadily spreading northeast as the low levels saturate giving isentropic lift more moisture to tap into. The biggest issue today will be the eastward drift of the 5h trough axis, which will help shift the best lift and moisture along or just off the coast. Inland areas will remain dry, although an isolated sprinkle cannot be ruled out. Closer to the coast some light rain will be possible, especially in SC, but amounts will be low. Most areas will see little more than a few hundredths (at best) with the highest amounts remaining under a tenth of an inch. Northeast flow and cloud cover will keep highs close to 10 degrees below climo. Only changes for the morning update were to tweak precip chances and introduce pop a little earlier along the SC 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 /18Z THURSDAY THROUGH MONDAY/...
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As of 18Z...High pressure to our west will give us fairly decent aviation weather today with a predominately mid cloud ceiling. A weak wave will ride up the eastern seaboard this evening. Still some uncertainty with respect to rain and ceilings, but think the coast has a decent enough probability to introduce some light rain, just before 00Z at the Myrtles. Ceilings will be lowest there also, but should remain VFR. VFR conditions are expected on Friday with northeast flow. Extended Outlook...Possible showers along the coast Saturday night, otherwise VFR.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 10 AM Thursday...Northeast surge continues this morning with speeds close to 20 kt. Gradient will briefly relax around midday into the early afternoon before tightening back up as the first in a series of weak surface waves moves up the coast. Inherited small craft advisory will remain unchanged for now but it is possible it will need to be extending in time to account for a return of northeast flow around 20 kt later this afternoon and overnight. Seas continue to range from 3 ft near shore to 6 ft close to 20 nm. 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...III SHORT TERM...DCH LONG TERM...MJC AVIATION...DL

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