Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 121200 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 700 AM EST Fri Jan 12 2018 .SYNOPSIS... The last day of the "January Thaw" is upon us. Low pressure over the lower Mississippi Valley will move northeastward along a cold front, that will reach the Carolinas late this evening and overnight. Expect widespread 70s for highs today along with showers and maybe a rumble of thunder late this afternoon into tonight. A cold frontal passage will occur late tonight followed by much cooler and drier air infiltrating the region. A secondary cold frontal passage will occur by mid to late Sat morning followed by high pressure with Arctic origins. Expect cold and dry conditions Sun into Mon with a brief warm-up Tue of next week. A reinforcing shot of Arctic air early Wednesday will affect the area thru Fri. && .NEAR TERM /THROUGH TONIGHT/... As of 330 AM Friday...Our "January Thaw" is progged to come to an end this period. A transition back to a very cold longwave pattern will transpire during the short term period. Early this morning, the FA lies in between a large amplitude south to north upper ridge with it`s axis well off the East Coast of the U.S. And at the same time, a large amplitude nearly full latitude upper trof extends northward along the Mississippi River Valley and well northward into Canada. A mid-level closed low at the bottom of the upper trof is progged to open up and briefly negatively tilt as it accelerates NE, basically along the spine of the Appalachian Mountains to the PA/NY border by Sat daybreak. All of this has and will result in 2 main fluxes of northward moving pcpn, which includes the 1 affecting the FA currently. This will be followed by a "dry" period, relatively speaking, between late this morning thru mid to late this afternoon. This next or 2nd flux of pcpn will have additional dynamics that influence the possibility of isolated thunder. With 50+ kt winds progged to drop to 930mb at the peak of the pcpn activity, isolated strong wind gusts will be possible and may even occur with the stronger showers without thunder. As always for this time of the year, the lack of instability will limit convective development. Sea fog over the adjacent Atlantic waters as seen with GOES_16 10.3- 3.9 micron channel, will continue to plague the coastal waters and the immediate coast given the onshore direction of SSE-S winds thru early this evening. As winds veer to the SW during this evening and WSW overnight with drier air, sea fog development and resulting coverage will decrease and become non-existent by daybreak Sat. Temperatures are basically a confluence of avbl guidance with more emphasis with a slightly warmer bias with the NAM and GFS guidance. Will see widespread 70s for highs today except along the immediate coast where onshore flow over SSTS in the 40s will keep max temps in the 60s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...A return to winter occurs this weekend as two dry cold front cross the region, reinforcing a deep eastern CONUS trough into the Carolinas. One cold front will be offshore Saturday morning, but the true temperature-crashing boundary will exit the coast during the aftn. 850mb temps fall from around +3C to +5C early Saturday, to -3C to -5C Saturday night. Another boundary will cross the area Sunday evening, reinforcing the cold air and finally bringing the mid-level trough axis to the east. This is important because despite two cold fronts (late Friday and then again Saturday aftn), as the trough axis hangs back to the west, SW flow atop the surface wedge will keep moisture trapped near the surface much of Saturday so cloud cover will be extensive. This cloud cover combined with cold advection Saturday will keep temps much cooler than Friday, with highs near seasonable normals in the low to mid 50s, followed by mins Saturday night dropping into the upper 20s. Although the column will dry Sunday, continued cool advection and lower thicknesses will bring a return to abnormally cold weather, with highs only rising into the low 40s, and mins near 20 far NW zones, mid 20s SC coast. Of course this cold is all relative, as it will still be 10+ degrees warmer than what we experienced just last week. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 300 PM Thursday...A very progressive pattern will impact the eastern Carolinas this period. A deep longwave trough will be positioned across the eastern third of the nation with several shortwave troughs migrating through the base of the trough. Some lingering shortwave energy will be shifting off the coast on Sun. Another mid-level trough will follow during Mon. The amplified pattern will get reinforced with an upper low moving across the Great Lakes early in the week and then shifting S across the Ohio Valley and perhaps as far south as the Tennessee Valley. This low will then cross the central Appalachians Wed before lifting out across the Mid-Atlantic and New England states Wed night through Thu night. Although model solutions have not come to a consensus as of yet, and certainly this is not unusual, the Euro model is showing coastal trough development Mon night and Tue with an area of low pressure initiating off the Carolina coast Tue night and then moving well N of the area by/during Wed. If this scenario does unfold, there could be some precipitation on and near the coast. As far as precipitation type, at this point we will forecast a cold rain, but the window of above freezing temps and support for an all liquid event is not wide and so there could be a changeover to light frozen precipitation Tue night before ending. There is also some concern that as a vigorous shortwave pivots across the area, it could bring some light snow or flurries to portions of the area late Tue night or on Wed. Lack of model agreement keeps me from including POPs any higher than slight chance to small chance and will confine mentionable POPs to the coast for the time being. At the surface early next week, we expect high pressure to wedge down the coast. Temp profiles support below normal temps with 850 mb temps cooling as we move from Sun to Tue and as low as minus 5 to minus 9C. 850 mb temps will drop as low as minus 12 to minus 15C in the wake of the coastal low as Arctic air overspreads the region Wed and Thu. It does not look like a repeat of the magnitude nor certainly the duration of the last outbreak, but highs for much of the week will be in the 40s with perhaps only upper 30s to near 40 Wed and Thu. Lows will be mainly in the 20s and as cold as the teens, especially by Wed night. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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As of 12Z...VLIFR to IFR sea fog at KCRE/KMYR will persist through the day, with only tempo periods where improvement to IFR/MVFR will occur, which will be mainly during times of shower activity. KILM terminal may be just far enough inland to miss the dense fog/stratus and have indicated VFR at KILM for this morning, but will need to monitor. Inland terminals will be MVFR tempo IFR through the day. Models indicate a strong round of precipitation around noon today, with the bulk of the activity this evening. Thunderstorms remains a possibility, and have added to add to TAFs for this evening. Pcpn will end from SW to NE...by 02Z KFLO/KLBT and around 06Z at KILM. Extended Outlook...VFR. Gusty west to northwest winds will occur in the wake of a dry cold frontal passage Sat afternoon. The next cold frontal passage will occur late Tuesday with MVFR conditions possible due to isolated pcpn.
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&& .MARINE... NEAR TERM /THROUGH FRIDAY/... As of 345 AM Friday...SCA continues across all waters Dense sea fog is the main issue plaguing mariners across the local waters. This will continue thruout the day with pockets of rainfall alleviating the severity of the dense fog at times. Nevertheless, very mild and moist air, with sfc dewpoints in the 60s, will advect across SSTs in the 40s and keeping the sea fog machine pumping away into this evening. Winds just off the deck will increase to 35 to 40 kt by late this aftn and evening. However, it will be difficult to mix this mild air to the ocean sfc due to cold SSTs. Once CAA occurs late tonight after the initial FROPA, some of these stronger winds aloft will be able to mix to the ocean sfc as wind gusts. Will include isolated thunder with the 2nd influx of convection later this aftn and evening due to favoring dynamics. Overall SSE-SSW sustained windspeeds of 15 to 25 kt today thru this evening, with gusts up to 30 kt mainly immediately ahead of the cold front from mid- evening to just after midnight. Winds will veer to the SW at 15 to 25 with G30 kt after FROPA during the pre-dawn Sat hours. Already risen significant seas in the 5 to 8 ft range except up to 9 ft across the outer waters off Cape Fear and Romain respectively. As a westerly component in the wind field increases tonight, ie. after the CFP, seas will begin to drop by a foot by daybreak Sat. An ESE ground swell at 9 second periods will actually dominate the significant seas as seen and progged with Spectral Density (ie. Power) Charts for the local waters. SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... As of 300 AM Friday...One cold front offshore to start the period, while a secondary front will cross the waters Saturday aftn. This will cause winds to shift from west early, to NW during the aftn, and then N by Sunday morning, with speeds generally 15-20 kts regardless of direction. The large swell that has been plaguing the waters the past few days will erode during Saturday, so seas are expected to fall below SCA thresholds, to 3-5 ft, by Saturday evening as the wind wave becomes more significant within the spectrum. A surge of N winds will occur the first half of Sunday as another boundary pushes offshore and high pressure builds in from the NW. This will drive winds briefly back up to 20-25 kts and seas up to 6ft, and another brief SCA may be required before conditions improve at the end of the weekend. LONG TERM /MONDAY THROUGH TUESDAY/... As of 300 PM Thursday...High pressure will wedge across the Carolinas Sunday. A coastal trough is expected to develop offshore early next week and some of the models are showing an area of low pressure initiating off the Carolina coast Tue or Tue night. Confidence in where and when this low develops is low. Northerly winds will be mainly in the 15 to around 20 kt range into Mon. Wind speeds should decrease to 10 kt or so late Mon and Mon night. Seas will be 4 to 5 ft Sun with some residual 6 ft seas possibly lingering across the northern waters. Seas should only very slowly subside to 3 to 4 ft late Mon and Mon night. && .ILM WATCHES/WARNINGS/ADVISORIES...
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SC...None. NC...None. MARINE...Dense Fog Advisory until 6 PM EST this evening for AMZ250-252- 254-256. Small Craft Advisory until midnight EST Saturday night for AMZ250-252-254-256.
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&& $$ SYNOPSIS...JDW NEAR TERM...DCH SHORT TERM...JDW LONG TERM...RJD AVIATION...MRR

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