Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 211816 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 110 PM EST Sat Jan 21 2017 .SYNOPSIS...
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A warm front over the NC/SC border will lift north through tonight as low pressure moves up into the Carolinas. A more complex and potent storm system will affect the Carolinas Sunday into Monday with potential for severe weather during Sunday afternoon and evening. Total rainfall amounts today through Monday should amount to one to three inches. This storm system will slowly depart through Monday leaving high pressure for Tuesday and Wednesday. The next cold front will move across the area on Thursday.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 1100 AM Saturday...Dense Fog Advisory has expired for all areas across the forecast area as fog lifts and visibilities continue to improve. Frontal boundary remains draped from west to east almost directly cutting the NC/SC border with some light pcp along and off the coast. Area of heavier rain with isolated thunderstorms was just creeping in from the south into northeast SC. This boundary will shift north back north as warm front through early this afternoon. Sfc winds will come around leaving a deep warm and moist S-SW flow across the area. Models continue to show a sfc low moving along this boundary as a shortwave tracks up from the SW. As the low exits off to the north overnight the boundary will get a slight push south again but it looks like it should be aligned closer to the VA/NC border by Sun morning leaving our forecast area well entrenched in a warm and moist air mass overnight. The best shortwave energy will move across the area this afternoon through this evening with periods of heavier rain and isolated thunder possible. Strongest convection will remain west aligned with low which should move through the western Carolinas between 4 and 8pm. Expect a break in pcp overnight with another period of low stratus and fog with temps and dewpoints remaining near 60. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 445 AM Saturday...This will become a busy period of changing wx conditions due to the progressive flow basically occurring at all levels. All eyes turn toward the potent upper closed low over Louisiana at sunrise Sunday. This closed upper low does intensify as it moves from Louisiana ENE to the Western Carolinas by daybreak Mon. Looking at the GFS, European, NAM and SREF model comparisons...and for the most part they all agree thru 72 hrs with the mid-level closed Low over Virginia by Monday evening. Its the time line there-after is when the models diverge from one another`s solutions. For Sunday thru Sunday night, is the time period when the upper low captures the sfc low. By Sunday evening, an occluded front will extend from the captured low to the Carolinas Coasts. Aloft, the dynamics associated with the upper closed low along with the twisting and turning of the winds from the sfc to aloft will favor a hodograph that signifies tornadic possibilities. Will definitely have the wind shear from both increasing speeds from the sfc thru aloft and also wind shear in terms of wind direction changes as one goes up thru the atmosphere. The amount of instability avbl will be in question in order for this severe wx to materialize. The old saying, high Shear, low Cape maybe just enough input from each for svr thunderstorms to develop with this event. I`ve seen where 60+ kt winds were howling less than 1200 ft AGL, but with no avbl CAPE for thunderstorm activity to develop and tap those low level jet winds in bringing them down to the sfc. The overall time-line SVR Threat will be from Sunday mid to late afternoon across the SW portions of the ILM CWA...moving across and exiting NE of the ILM CWA by mid to late Sunday evening. Will highlight the Severe potential in the Hazardous Weather Outlook. The stacked low will drift across VA and off the VA Cape by Tuesday daybreak. The sfc cold front pushes well east of the FA late Sunday night thru Monday. Enough moisture will wraparound aloft, keeping the FA within cloudiness along with a low POP for either light showers or patchy light rain or drizzle. There just isn`t any cold air avbl for any type of Wintry Pcpn chances to worry about given this type of system and the Winter season we are currently are in. Overall, temps thru this period will start well above normal, ie. 15 degrees above normal. And will end with temps 5 to 10 degrees above normal. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 300 AM Saturday...Impressive stacked low will be exiting to the northeast Tuesday morning with weak mid level ridge axis to the west shifting overhead. 5h ridge does expand north slightly Tue into Wed, increasing mid level subsidence, but it shifts off the coast by midday Wed. Under the mid level ridge a weak surface high will build in from the west. The high is a modifying maritime tropic airmass and lacks cold air. As a result temperatures Tue and Wed will remain well above climo. Mid level subsidence and a lack of deep moisture helps keep the region free of precip as well as limiting cloud cover. A cold front, trailing low pressure moving from the eastern Great Lakes to southeast Canada Wed into Thu, moves into the area Thu. Deep southwest flow ahead of the front will help spread Gulf moisture over the region. Precipitable water values approach 1.5 inches just prior to fropa and there should be some potential for isolated showers, especially if a slower solution similar to the latest GFS, verifies. GFS also depicts a weak wave developing along the front prior to the boundary reaching the forecast area. ECMWF is a little faster with the front (in part because it doesn`t develop the surface wave). While temperatures ahead of the front will be well above climo, the passage of the front begins a downward trend in temperatures as another high builds in. Temperatures will be near climo for Fri and then below climo on Sat. The cold air does not arrive in 1 big surge, instead it oozes into the southeast over a period of a couple days. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 18Z...Difficult flight conditions as periods of IFR and MVFR prevail this TAF cycle. The onshore flow will also plague coastal terminals at times with VSBYS < 1/2 NM. -RA/SHRA also in the mix 22Z-02Z, then again Sunday AFT 14Z. Winds mainly SSE-SSW this period at speeds of 11KT or less. Extended outlook...Thunderstorms are expected on Sunday with IFR conditions possible. There is potential for strong to severe thunderstorms Sunday afternoon into the evening. Monday thru Wednesday, MVFR to mainly VFR conditions expected. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 100 PM Saturday...Dense Fog Advisory issued for all waters for areas of fog with vsbys less than a mile. SCA for all coastal waters beginning at 6 am Sunday and persisting thru 6 pm Tuesday. A sfc frontal boundary will move back north as a warm front as low pressure tracks up into the Carolinas through this evening. Winds to the north of this boundary will shift from E-SE to S-SW and south of the boundary the winds will be S to SW. Winds 10 kts or so will pick up to 10 to 20 kt by daybreak Sunday. Overall the local waters will remain in the warm sector under increasing S to SW winds. Will indicate isolated thunder, mainly across outer waters. Significant seas will be at their lowest today when compared to what they will become during the next 3 days. The seas will begin their rising trend tonight with 3 to 5 footers possibly by daybreak Sunday. Wind driven waves at 5 to 6 second periods, will dominate the significant seas spectrum this period. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 445 AM Saturday...SCA thresholds to be met by Sunday morning and will persist thru Tuesday daybreak. Much will depend on the behavior and potential strength of the mid-level closed low that captures it`s sfc companion and becomes vertically stacked by the end of this period. For 2 to 3 days out, the big 4 models are in decent agreement with one another with regard to the intensity and timing of this eventually stacked system. When you observe 990`s and 980`s sfc lows being advertised across the ILM CWA, then for Marine purposes, a SCA is a "given" with an increased potential for Gale Warnings may be needed especially when models indicate 980`s sfc lows moving in the vicinity. I may be underdone with the winds for Monday as I remained somewhat skeptical of various model solutions. Will be looking atleast at 20 to 30 kt windspeeds with hier gusts. Significant seas will have already been on the increase at the start of this period. Ww`ll likely be pushing atleast 10 ft just outside of the ILM coastal waters off Cape Fear and Romain. The only "saving grace" is that winds will be veering to the WSW to WNW, ie. Offshore trajectory, late Monday, thus limiting the avbl fetch for significant seas to build upon from. LONG TERM /TUESDAY THROUGH WEDNESDAY/... As of 300 AM Saturday...Strong offshore flow to start the period will gradually subside during Tue as high pressure builds in from the west. Conditions Tue morning will likely require headlines but unsure if SCEC or SCA will be warranted. Gradient gradually relaxes Tue with speeds dropping under 15 kt Tue night as winds veer from northwest to southwest. Surface ridge axis moves overhead Wed morning with speeds around 10 kt. Ridge axis shifts offshore Wed with a steady increase in southwest winds in the afternoon and evening. Solid 15 kt southwest winds Wed afternoon will increase to 15 to 20 kt Wed night. Offshore flow Tue leads to a steady reduction in seas, dropping from near SCA thresholds Tue morning to 1 to 3 ft Tue night. Southwest flow developing and then increasing Wed will start building with values peaking between 3 to 5 ft late Wed and Wed night.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Dense Fog Advisory until 6 AM EST Sunday for AMZ250-252-254- 256. Small Craft Advisory from 6 AM Sunday to 6 PM EST Tuesday for AMZ250-252-254-256. && $$ NEAR TERM...RGZ SHORT TERM...DCH LONG TERM...III AVIATION...8

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