Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 132321 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 721 PM EDT Tue Mar 13 2018 .SYNOPSIS... Strong low pressure off the New England coast will continue to move slowly north through tonight. Arctic high pressure across the Northern Plains will build south through tonight and then east across the northern Gulf Coast Wednesday and Thursday. Temperatures will warm Thursday and Friday before another shot of cold air reaches the area Friday night and Saturday. Warmer, but cloudier weather will return early next week, with another storm system approaching by Tuesday. && .NEAR TERM /THROUGH WEDNESDAY/... As of 600 PM Tuesday...After in-house met discussion including 18Z guidance, decided to go with a Freeze Warning along the northern periphery of the ILM CWA, which includes the 6 most northernmost counties for the time between 4 am and 9 am Wed. Could see a brief decouple of the winds this evening but should pick back up after midnight tonight as a mid-level s/w trof rotates thru late. Could see a shallow stratocu or altocu cloud deck partially affect the FA overnight into daylight Wed but most of that should remain north of the FA. Latest MOS guidance still wants to paint 30-32 degree lows tonight and this is taking into account what in essence should keep min temps slightly hier overnight. This will not be a deep freeze, that may manifest come Thu morning. Previous....................................................... As of 300 PM Tuesday...Downsloping westerly mid level flow will back to SW overnight ahead of strong approaching clipper-like shortwave. This feature sets up an interesting if not slightly uncertain forecast for our northern (particularly agriculturally sensitive) forecast zones. Specifically, the need for a Freeze Warning is unclear at this time due to some conflicting signals. Temperature guidance depicting at least marginally freezing temperatures for a short time tonight. However these same MOS numbers seem to be at odds with their parent guidance. The latter shows that clouds increase with the shortwave whereas the former MOS bulletins hint at clear skies all night. Am leaning towards the clear sky solution being erroneous as there is clearly a large swath of cloudiness currently associated with the circulation and vort center (though that could change on the leeside of the mountains). Flurries associated with this same feature has been discussed but they should remain to our north if they materialize at all. Hopefully during the next shift temperature and cloud cover trends will shed more light on the need for a Freeze Warning. The renewed cold air advection underway by 12Z will keep highs every bit as chilly if not colder than those observed today. && .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...The deep upper trough will begin to lift out from the East Coast, but a pair of shortwaves embedded in the jet will maintain cyclonic curvature to our upper level flow through Thursday. A sharp upper ridge across the High Plains Wednesday night will deamplify as it moves into the Arklatex region by Thursday night. At the surface, Canadian high pressure will move eastward along the Gulf Coast, crossing Florida on Thursday and moving offshore Thursday night. Wednesday night is likely to be the coldest night of the week across the Eastern Carolinas as lighter winds with the surface high to our southwest combine with a cold airmass and clear skies. Models have stabilized over the past 36 hours with their depiction of low temperatures in the upper 20s inland and lower 30s near the coast. I`ve knocked off several degrees from these numbers across the peat/pocosin soils mainly across southeastern North Carolina with lows predicted as cold as 25 degrees in spots. This is unfortunately where many of our local blueberry/strawberry farms are located, and growers are hopefully preparing for this freeze event. As a surface trough moves off the Mid-Atlantic coast Thursday afternoon/evening, our pressure gradient will tighten substantially. Warm advection on westerly winds should allow highs to rebound into the 60s area-wide, with wind gusts during the afternoon potentially reaching 30 mph. Lighter breezes will continue through Thursday night, helping hold low temperatures in the 40s and perhaps near 50 on the beaches. Models show a strong mid and upper level WNW wind across the Appalachians with a subsidence inversion sitting just above the ridge tops Thursday night, a scenario sometimes associated with orographic cirrus development. Should this occur, we might need to add a few more degrees to Thursday night`s lows. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 PM Tuesday...The East Coast trough will continue to lift to the northeast on Friday, as a low-amplitude mid/upper ridge crosses the Mississippi River valley. This will allow a surface high to surge southeast and push a backdoor cold front into or through the forecast area Friday night. Will carry low PoPs as Gulf moisture surges across the area ahead of fropa. The cool high will settle over eastern NC Saturday ahead of a quick moving shortwave and surface reflection which will move across the Carolinas Saturday night, and offshore Sunday. Associated rain chances will come to an end late Sunday, and temps will rebound from Saturday`s unseasonable cool readings, but still remain 3-5 below climo. The pattern will remain quite progressive early next week, with another shortwave and associate surface low on the doorstep by Tuesday. && .AVIATION /23Z TUESDAY THROUGH SUNDAY/...
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As of 00Z...VFR this TAF valid period. An upper impulse with a corresponding surface reflection will pass around midnight Z. Light winds will become light northwest with 6K cigs most likely northern terminals. After 14Z northwest winds will increase with gusts 20-25 kt. Scattered to broken mid clouds expected with best cig potential KLBT-KILM. Extended outlook...VFR through Friday. Possible MVFR Fri night and Sat.
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&& .MARINE... NEAR TERM /THROUGH WEDNESDAY/... As of 615 PM Tuesday...Winds and seas have dropped below SCA thresholds and have let the SCA expire with the issuance of a MWW. But did highlight, SCA thresholds will again be met during Wed daylight into nightfall. This after the passage of a mid- level s/w trof that re-tightens the sfc pg after its departure early Wed. Winds will drop to W to WNW around 15 kt this evening and become NW 15 to 25 kt occasional G30 kt by or just after daybreak Wed, that continues thruout the day on Wed. Significant seas will be on the low side due to the limited fetch given wind directions for seas to build upon. There is a roughly 1 to 3 foot Easterly ground swell at 12+ second periods that will be pushing across the local waters during the next few days which will help produce a wider than normal margin for significant seas fcsts across the local waters this period. Previous................................................... As of 300 PM Tuesday...Wind remains as-is or even slackens slightly through about 06Z as very weak surface reflection of a powerful upper level system approaches from the northwest. After 06Z this feature moves through and flow turns to NW in a renewed surge of cold air. Wind could briefly pulse up to SCA levels but confidence is a little too low to raise flags at this time. Any 6 ft seas remain outside of the 20nm forecast zones according to both WNA and locally generated NWPS. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Canadian high pressure will take a path eastward along the Gulf Coast, crossing Florida on Thursday and moving offshore Thursday night. With the high so far to our south, we`ll maintain an offshore wind through the period. Unfortunately this is likely to be a strong offshore wind developing during the day Thursday and continuing through Thursday night as a trough moves off the Mid-Atlantic coast, tightening the pressure gradient substantially and accelerating our winds to 20-25 knots with gusts near 30 knots away from shore Thursday night. It`s a near certainty that we`ll need a Small Craft Advisory beginning Thursday afternoon. .LONG TERM /FRIDAY THROUGH SUNDAY/... As of 300 PM Tuesday...Offshore flow will be the rule Friday as surface high pressure moves off the east coast of Florida. A cold front will drop south across the waters Friday evening, with a quick shift to northeast winds. High pressure behind the front will move off the east coast of NC Saturday, and result in onshore flow through the day. The gradient will strengthen behind the front in the NE surge, and winds may reach into a 15-20 kt range late Friday night into Saturday morning. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Freeze Warning from 4 AM to 9 AM EDT Wednesday for SCZ017-023- 024. NC...Freeze Warning from 4 AM to 9 AM EDT Wednesday for NCZ087-096- 105. MARINE...None. && $$ SYNOPSIS...MBB NEAR TERM...DCH/MBB SHORT TERM...TRA LONG TERM...TRA/CRM AVIATION...MRR is the U.S. government's official web portal to all federal, state and local government web resources and services.