Area Forecast Discussion
Issued by NWS Wilmington, NC

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746 FXUS62 KILM 211452 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 952 AM EST Tue Nov 21 2017 .SYNOPSIS... A coastal trough just off the Carolina coasts and an approaching cold front from the northwest will combine to produce light pcpn late this afternoon thru tonight...with the coastal areas seeing the best shot of seeing measurable rainfall. High pressure will follow and slowly build in from the west Wednesday thru Friday. At the same time, low pressure will pass just south and east of the area Wed night thru Thu with the immediate coast again seeing the best chance for rainfall. A strong cold front will approach from the west during Sat and will sweep across the forecast area and off the coast to well offshore by late Sat night. Strong, dry and cold Canadian high pressure will follow Sunday thru early next week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 930 AM Tuesday...Coastal trough offshore today will try and make its way west. However it may struggle to do so into tonight as weak surface wave/low moves up the coast. Surface low in eastern TX would normally help the trough move onshore, but this feature is pushed south by another shortwave dropping south through the impressive 5h trough. The first in a series of shortwaves rounding the base of the trough later today will head up the Southeast coast this evening and overnight, lifting the developing surface wave/low with it. Isentropic lift will generate some light to moderate rain along and just off the coast overnight. If the trough does briefly move onshore it would be most likely to do so during the first half of the evening and would lead to slightly higher rainfall rates along the immediate coast. Did not make a lot of changes to previous forecast but did slow northward progression of rain a little bit. Cloud cover will keep highs in the 60s today with inland areas, which started out 5 to 10 degrees cooler than the coast, ending up in the lower 60s while the coast will reach upper 60s.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 330 AM Tuesday...First thing Wednesday morning, weak low pressure accelerating ENE, will be pulling away from the FA taking any patchy pcpn and cloudiness with it. A coastal trof along the immediate coast, will get pulled back over the Atl waters during the morning. A cold front will drop from the NW, and sweep across the FA by midday and off Carolina coasts before stalling offshore and parallel to the coastline Wed night. Will observe partial clearing during Wed aftn and evening as weak CAA occurs via partial thicknesses schemes ie. 1000-850mb along with 850mb temps dropping. Max temps will run in the mid 60s slightly cooler than MOS guidance but normal for this time of the year. Min temps Wed night will also run about normal with lows in the upper 30s to low 40s. For Thu thru Thu night, models are defying unity with respect to the final wx outcome of this time period. This is in reference to a northern stream 5H s/w trof that drops to the SE States during Thu and progresses eastward Thu night. Sfc low pressure will develop along the stalled front offshore from SC late Thu and accelerates to the ENE Thu night, pulling away from the ILM CWA. The European and to a degree the NAM are both drier than the GFS fcst. This likely due to a less amplified or a flatter 5H s/w trof when both compared to the GFS. Will stay closer 12 UTC guidance has jogged eastward. I did trend the forecast into a dry bias, where the sfc low with best POPs and QPF staying off the ILM CWA Coast. Will still exhibit low chance POPs, mainly well east of the I-95 corridor to the immediate coast. By daybreak Fri, any pcpn and cloudiness across the FA will be accelerating off to the ENE, away from the FA. For Max temps Thu, will see widespread 50s via European MOS due to clouds and low chance pcpn. On a side note, the wetter GFS MOS Guidance indicates upper 40s for Thu highs well inland, ie. along and west of the I-95 corridor. Friday morning lows will exhibit climo norms, with upper 30s to near 40 covering it. && .LONG TERM /FRIDAY THROUGH MONDAY/... As of 245 PM Monday...The extended forecast will be mostly influenced by an almost standing wave trough across the eastern third of the conus. Ridging will remain focused across the four corners region. There remains some indication of a couple of systems moving across the baroclinic zone to the east but the 12 UTC guidance has jogged eastward. I did trend the forecast in the early periods a little drier so its essentially a dry forecast throughout. Overall temperatures will run a little below normal starting out on the cooler side of climatology with a brief warmup for the weekend. This will be followed by another cold shot early next week. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... As of 12Z...Mainly jet cirrus today. A developing low pressure system near Florida will track up the eastern seaboard this evening, bringing a chance for rain mainly at the coastal terminals. After the low passes to the northeast, winds will swing around to northwest, with a brief period of IFR ceilings/vis expected. Conditions should improve after daybreak on Wednesday. Extended Outlook...MVFR conditions may develop in low clouds and light rain early Wednesday morning,. VFR Thursday. MVFR to IFR conditions are possible late Friday into Saturday in low clouds and rain. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 930 AM Tuesday...Weak coastal trough over the waters today and tonight will keep winds light, generally 10 kt or less. Direction will vary between N-NE to E-SE depending on the location of the trough, which will try and move onshore late in the day. Confidence is low on whether or not the trough will move onshore but regardless of its location the weak gradient will maintain light winds well past midnight. Late in the period, as cold front moves east of the waters, offshore flow will develop and speeds will increase to 10 to 15 kt. Lack of any real cold advection limits gust potential. Seas around 2 ft this morning will build as surface wave to the southwest moves northeast, peaking at 3 to 4 ft late in the period. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 330 AM Tuesday...Wednesday will be highlighted with CAA under northerly winds in the morning veering to the NE in the aftn and night. Wind speeds will run 10 to 20 kt Wed into Wed night as CAA and a tightened sfc pg contribute to the winds. With significant seas building to 3 to possibly as high as 6 ft during Wed night into Thu. Majority of the seas will come from short period, 5 to 6 second wind waves. For Thu thru Thu night, depending where the sfc low develops and intensifies relative to the ILM Coastal Waters, will determine both winds and locally produced seas. GFS again wants to intensify a low that is just short of a Gale late Thu. Will follow this trend but keep the low further offshore along with the best sfc PG. Will definitely see SCEC and possible SCA conditions Thu into Thu night and will highlight in the Hazardous Wx Outlook. Sig. seas will hold in the 3 to 6 ft range Thu into Thu night with a few 7 footers possible. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 245 PM Monday...Northeast winds of 10-15 knots will prevail through the first two days of the extended marine forecast. There may be a few hours of 15-20 early on but overall 10-15 should do it. By Saturday a modest southwest flow will develop ahead of another cold front which should move across later in the weekend. Significant seas will trend downward from 3-5 feet early to 2-4 and possibly 1-3 feet by Saturday.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...III SHORT TERM...DCH LONG TERM...SHK AVIATION...DL

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