Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 221137 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 637 AM EST Sun Jan 22 2017 .SYNOPSIS... A complex and potent storm system will affect the Carolinas today through Monday with potential for severe weather during late this afternoon and evening. Total rainfall amounts through Monday should amount to one to 2 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. Much colder weather will follow Friday and into next weekend. && .NEAR TERM /THROUGH TONIGHT/...
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As of 630 AM Sunday...Two more rounds of pcpn will affect the ILM CWA during the next 24 hrs. The 1st is currently now overhead with mainly stratiform rains with embedded heavier showers. The pcpn from Sat evening helped to stabilize the airmass across the FA prior to this next pcpn area. The embedded thunderstorm activity over GA and southern SC will fall apart by the time it reaches the ILM CWA during this morning. QPF from this pcpn round will run around one quarter of an inch for the ILM NC CWA up to one half inch or slightly hier for the ILM SC CWA. Will see a brief reprieve from the pcpn from midday thru mid-afternoon. The next round of pcpn, and potentially the more potent, will occur from late this afternoon through late this evening. The pcpn will overspread the FA from SW to NE. A closed upper closed low will move from the Gulf Coast States this morning, to the western Carolinas this aftn thru tonight. It`s accompanying sfc low will quickly get captured by this upper closed low later today...and become a somewhat vertically stacked system by Mon daybreak. Plenty of dynamics aloft and at the sfc will be in play with this next round of pcpn. As for severe convection potential, the FA will experience a High Wind Shear environment and a Low Cape, instability environment. Do not need much instability when you are dealing with plenty of atmospheric dynamics, especially this much low level wind shear. Thus, with plenty of twisting in the low levels, rotating tornadic type thunderstorm activity is possible beginning late this aftn thru this evening. Will advertise the possible tornadic threat with damaging wind gusts and hail. The low`s occlusion portion of it`s frontal system, will push across the FA from west to east during the mid to late evening hours. After pushing thru, the pcpn will come to an abrupt end. A dry mid-level punch is the mechanism for pushing this occluded front across the ILM CWA and likely where you will find the most intense pcpn prior to it pushing thru. Will indicate isolated showers after it`s passage for the remainder of the overnight. Temperatures will run up to 15 degrees above normal this period. The CAA after the pcpn comes to an end will lag-some, with the best of it occurring during the next period. As a result, do not expect your normal diurnal temperature curve this period.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
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As of 430 AM Sunday...The Fa will be under the mid-level dry air associated with the "dry punch" that pushed across Sunday night. During Monday, expect the wraparound moisture to push across the FA associated with the Closed Upper Low moving from the western Carolina to only off the DELMARVA Coast by Tue daybreak. Dynamics from weak mid-level vorts rotating around the slowly lifting upper closed low will result in low topped isolated to scattered showers across the FA, especially during the daytime heating on Mon. This pcpn threat will diminish quickly after nightfall Monday. However, low level clouds will continue to persist thru Monday night. For Tuesday, the WNW-NW downslope wind directions thru the atm column will scour out any remaining moisture resulting in finally a Sunny sky for Tuesday and a Clear Tue night. Temps thru the period will slightly lower from each previous max and min temp occurrences. The exception may be for Tue highs when a downslope trajectory may add several degrees to Tueday`s highs. The CAA will end Tue morning with various thickness schemes rising indicative of WAA especially aloft. Overall, followed a consensus amongst the avbl model Mos Guidance except for Tue highs where several degrees were added due to ongoing WAA and the downslope trajectory thru the atm column.
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&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
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As of 3 AM Sunday...Period begins warm and dry with surface high off the east coast and mid level ridge axis overhead. Ridging aloft shifts off the coast during Wed but subsidence will continue suppressing upward motion while pushing highs close to 70 degrees. Cold front moves across the area Thu morning possibly accompanied by isolated showers, however low level convergence is weak and the front lacks strong dynamical support. Inherited low chc pop may be a little generous but will not make any changes at this time. Regardless of shower coverage any rainfall would be meager if forecast soundings are correct in showing a brief 6 hour period of precipitable water values over 1 inch. By Thu afternoon PWATs are around 0.30 inch. Following the cold front cooler air will start building into the region, but its arrival is likely to be later Thu which will result in one last day with temperatures above climo. 850 temps drop 5-10 degrees C between Thu morning and Fri morning and highs on Fri may struggle to reach climo (mid 50s). Temperatures will trend even cooler for the weekend with a reinforcing shot of cold air Sat keeping highs around 50 with lows hover around freezing. Deep westerly flow will keep skies mostly clear and prevent any rainfall.
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&& .AVIATION /12Z SUNDAY THROUGH THURSDAY/... As of 06Z...With the exit of the 1st round of pcpn, the FA has become more stable due to the subsidence in the wake of the pcpn now exiting off the Outer Banks. Sfc SSW-SW winds will remain active across the FA keeping dense fog development to a minimum early this morning. As winds back to the SSW and S later this morning, will have to keep an eye on any sea fog development and any inland push to it. The next round of pcpn is already making headway from the Gulf Coast states as a warm front lifts northward early this morning. This pcpn should be pushing across the FA from SW to NE, roughly between 08Z thru 15z. The pcpn will be moving over an airmass that has been stabilized and thus the thunderstorm activity, if any, will be held to a minimum. And finally, the final round of pcpn, with an increased potential for severe Thunderstorms, will occur between 1/22 at 21Z thru 1/23 at 05Z. This will be associated with the intensifying upper closed low and its accompanying sfc low, both finally lifting NE from the Gulf Coast States to the western Carolinas by 1/23 06Z. The dry punch in the mid-levels will push across the area during the mid to late evening hours, ending the pcpn after pushing across. Plenty of atmospheric dynamics associated with this final round of pcpn along with a meandering sfc boundary. Enough to warrant placing Gusts up to 45 kt during the convection this evening. Extended outlook...Expect mainly VFR, except for possible MVFR/IFR during Mon from clouds and reduced vsby from pcpn. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 400 AM Sunday...SCA all waters thru Tue afternoon. Looking at SSW to SW winds increasing to the 15 to 25 with gusts to 30 kt this aftn and evening. Some guidance indicates winds may temporarily back to the SSE-SE prior to the pcpn ending. For now, will hold onto the SSW-SW directions. The cooler shelf waters will help prevent the higher winds just off the deck from reaching the sfc. The possible convection moving across the area waters will have the capability to tap those stronger winds aloft and bring them down to the ocean sfc. This will be advertised in the Hazardous Weather Outlook. Significant seas will build to 5 to 8 ft by late this aftn and persist in the 6 to 9 foot range tonight...highest off Cape Fear. Wind driven waves at 4 to 7 second periods will dominate the significant seas. An underlying 10 second period 1 to 2 foot easterly ground swell will remain present. SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 400 AM Sunday...SCA will be ongoing at the start of this period and will extend thru 6 pm Tuesday. Cyclonic flow aloft and at the sfc will dominate the local waters thru Tuesday. This due to a closed low and it`s accompanying sfc low, now stacked" moving from the Western Carolinas to off the DELMARVA Coast Tue morning, and to off Cape Cod by Wed morning. Sfc ridging from Florida will extend northward across the local waters Tue night. A tightened sfc pg will be ongoing at the start of this period and will very, very slowly relax with time. Looking at SCA speeds Mon into Tue, with SCEC speeds late Tue and Tue night. Directions will run SW becoming WSW late Monday...and W to WNW during the day on Tuesday. Decent CAA Mon into early Tue will help keep the winds elevated. Significant seas thru Monday Night will run 4 to 7 ft, except up to 8 ft south of Cape Fear to Little River Inlet during day Mon night due to the fetch associated with the westerly wind direction. Seas will finally subside late Tue aftn thru Tue night to a 2 to 4 foot range, except remaining somewhat elevated across the waters south of cape fear to Little River Inlet due to the fetch associated with westerly wind direction. LONG TERM /WEDNESDAY THROUGH THURSDAY/... As of 3 AM Sunday...Southwest flow around western side of high pressure will gradually increase Wed and Wed night as gradient increases ahead of a cold front. Front moves across the waters late Thu morning with offshore flow developing in the afternoon. Ahead of the front southwest winds will peak around 20 kt Wed night and Thu morning. Winds veer to west-northwest Thu afternoon with speeds remaining 15 to 20 kt into Fri morning. Seas 2 to 3 ft at the start of the period will build to 3 to 5 ft later Wed and could exceed 6 ft in some areas late Wed night. Cannot rule out short duration SCA just prior to the front passing. Post front offshore flow will knock seas down, from 3 to 5 ft Thu afternoon to 1 to 3 ft Fri morning.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory until 6 PM EST Tuesday for AMZ250-252-254- 256. && $$ SYNOPSIS...III NEAR TERM...DCH SHORT TERM...DCH LONG TERM...III AVIATION...DCH

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