Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 120830 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 330 AM EST Tue Dec 12 2017 .SYNOPSIS...
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Today will be breezy and the warmest day of the week. The passage of a strong cold front later today will usher in Arctic air tonight and through Wednesday night. Temperatures will quickly moderate Thursday and Friday. A cold front may bring some light rain Friday and a brief cool down Saturday before seasonable temperatures return Sunday followed by the risk for showers on Monday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM Tuesday...KLTX VAD wind profile showing that just above the well defined surface-based inversion low level jetting is increasing, already up to 30kt at 1kft. This is in response to the strong upper trough and surface cold front approaching from the NW. Low level wind fields will remain this strong or even strengthen another 5kt through daybreak, the ramifications of which mainly confined to aviation. Given a little daytime heating however gusty winds should quickly materialize at the surface soon after sunrise. The resulting rapid erosion of the inversion should lead to an impressive temperature spike (15 degrees from 14-15Z?) followed by more typical if not slightly rushed rises in the moderately strong prefrontal WAA regime. By midday into early afternoon the front will rapidly cross the region, reversing the diurnal temperature curve as afternoon values drop rather quickly and the still gusty winds turn to the NW. Almost ironically tonight`s temperature curve may be fairly typical due to conflicting/offsetting factors. It will be breezy enough for mixing and thus normally a slower, flatter temp curve. This will be offset by the fairly robust CAA behind the front.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/...
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As of 300 AM Tuesday...The Arctic surge will drop dewpoints into the single numbers and teens on Wed as 850 mb temps drop as low as -11C. It will be sunny and cold with highs in the lower to mid 40s. NW to W winds of 10 to 20 mph will make it feel as if it were below freezing for much of the day. Minimum relative humidity will be as low as 25 to 30 percent Wed afternoon. As one deep trough lifts out Wed, another will begin to dig more modestly across the Great lakes and Midwest and then across the east coast late Wed night and Thu. It now looks like the brunt of the cloud cover will brush us by to the N. However, an impressive wind field will overspread the area with 50-60 kt of wind lowering to around 2 kft. These very strong winds will tend to keep the air near the ground moving and with the brunt of the cold and dry advection having passed, it should not be as cold Wed night. We should see dewpoints recover Wed night with low temps no lower than the upper 20s and lower 30s. The strong winds in the lower levels of the column will lift out Thu and under the influence of SW flow, highs should reach the mid 50s with plenty of sunshine. Light surface winds will return Thu night and we will begin to see clouds increasing from W to E ahead of yet another deep trough and surface cold front. These clouds will cap minimums in the mid and upper 30s with lower 40s at the coast.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/... As of 300 PM Monday...The East Coast longwave trough will reload late this week as another strong shortwave moves through the Carolinas on Friday. This upper system should induce low pressure to develop at the surface over North Carolina during the day Friday. Moisture is going to be tough to find given deep layer winds have so much offshore component, virtually eliminating Gulf of Atlantic inflow. In fact the only moisture I can find arrives in the 850-700 mb layer from the northwest -- most likely Pacific moisture that came onshore in British Columbia several days earlier. Dynamics are going to be so strong that I still think there will be some light measurable rainfall around, and I`m including a 30 percent chance of showers in the forecast for Friday. Dry weather will develop for Saturday and Sunday as a weak upper level ridge pokes north from the Caribbean and surface high pressure moves eastward along the Gulf Coast. Model depictions of another shortwave trough arriving on the East Coast Monday vary quite a bit from model to model, reducing confidence about what impacts we may see. PoPs of 30 percent have been introduced into the forecast for Monday along with some increased cloud cover. Temperatures will be on a roller coaster ride through the weekend, likely coolest on Saturday as the upper trough moves overhead and offshore. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 06Z...Though VFR expected through the period still not the smoothest of sailing for aviation concerns. Winds are very light/less than 5-7kt across the area as high pressure sinks into the Gulf. An approaching front and disturbance aloft will really tighten the gradient as the night wears on, increasing wind speed through the column. As the stalwart surface-based inversion holds strong this will mean a wind shear layer develops atop the inversion. By mid morning the inversion quickly mixes out for a windy afternoon in the prefrontal flow regime. FROPA will then bring a sharp change in direction by early afternoon. Wind may stay gusty through the evening albeit with a gradual decreasing trend. Extended Outlook...VFR.
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&& .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 300 AM Tuesday...Westerly winds to back to SW and increase ahead of a fairly sharp cold front approaching from the NW. Expect advisory criteria to be met by daybreak and continue through the period. The actual wind shift and FROPA will come late this afternoon and steepen wave faces while slightly decreasing nearshore dominant wave height as wave shadowing effects start to develop. SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 300 AM Tuesday...Small Craft Advisory conditions are expected to linger across at least portions of the waters Wed morning with the dry and cold surge slowly waning during Wed. However, a developing deep and strong WSW flow should keep winds elevated through much of the period. Winds will likely be near Small Craft Advisory criteria, 20 to 25 kt, Wed night into Thu with a 50 kt jet at 2 kft. Seas Wed morning will be highest offshore, up to 4 to 6 ft. Seas will subside during Wed before building to 3 to 5 ft Wed night into Thu with perhaps a few 6 ft seas across the outermost northern waters. Diminishing winds late Thu and Thu night will result in subsiding seas. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 PM Monday...An active and windy weather pattern will continue Friday as a Canadian cold front slides across the area. Low pressure is expected to develop along the front, helping produce a surge of offshore winds Friday night. The latest GFS model is actually showing gale-force winds Friday afternoon and night, but other model guidance is not that strong, instead keeping winds strong, but below 30 knots. Our forecast will go with this weaker wind forecast for now, implying a period of Small Craft Advisory conditions (W winds 20-25 kt) Friday into Friday night. Winds and seas should improve on Saturday as Canadian high pressure builds in from the west.
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&& .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Small Craft Advisory from 6 AM this morning to noon EST Wednesday for AMZ250-252-254-256.
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&& $$ NEAR TERM...MBB SHORT TERM...RJD LONG TERM...TRA AVIATION...MBB

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