Area Forecast Discussion
Issued by NWS Wilmington, NC

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656 FXUS62 KILM 102318 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 618 PM EST Sat Dec 10 2016 .SYNOPSIS... Arctic high pressure will maintain some of the coldest temperatures of the season through tonight. A warming trend will begin Monday as a coastal trough pushes ashore. A cold front will move into the area Tuesday followed by a stronger cold front Wednesday night. As a result, a chance of rain can be expected Sunday through Wednesday with colder temperatures returning Thursday and Friday. && .NEAR TERM /THROUGH SUNDAY/...
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As of 630 PM Saturday...Based on 6 PM observations I have lowered forecast lows by a couple degrees in the Wilmington area, with lesser changes at other cities. With such ideal radiational cooling conditions expected for the next 6-8 hours (calm surface winds, light winds at 1000 feet aloft, very dry air, clear skies) I have ramped our local "radiational cooling" tool up to its maximum setting. This local forecast editing tool takes soil type into account and cuts up to 7 degrees off model-blended low temperatures where peat/pocosin soils produce localized cold spots on calm, clear nights like tonight. Parts of the Angola Bay gameland in northern Pender County, NC could conceivably dip to 17 or 18 degrees by 3:00 AM! Discussion from 300 PM follows... Expansive high pressure centered near the TN VLY is ridging eastward across the Carolinas. This feature will continue to push to the E/NE tonight beneath fast and increasingly zonal mid-level flow. The combination of subtle warm advection off the surface and the shifting high pressure overhead will lead to rapid decoupling tonight, and winds will become nearly calm. Calm winds and clear sky conditions allow for good radiational cooling overnight, and mins are forecast to drop into the low to mid 20s away from the immediate coast. This is more in line with the cooler MAV numbers, as guidance tends to underestimate the lows during the 2nd, better radiational night, after a cold front. The exception to these colder temps will be very near the coastline, where a developing coastal trough late will turn winds more to the east, onshore, and may create some advecting stratocu late. So while temps inland will drop to values very close to last night, the coast should end up several degrees warmer, a degree or two either side of 30.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 230 PM Saturday...The moderating area of arctic high pressure will shift off the coast during Sunday while a weak coastal trough shifts onshore. The flow aloft will primarily be zonal through the period helping move a cold front into the area during Monday. Regarding moisture trends, expecting a sharp return of low-level moisture by Sunday afternoon. Although clouds will be returning during Sunday the level of saturation in the h7-h5 layer will be lacking. Isentropic lift will increase Sunday afternoon allowing rain chances to climb during the day, but more-so by Sunday night into Monday. The lack of deep moisture will preclude any significant QPF with this event with POPs carrying into Monday night. Temperatures will be somewhat complicated during Sunday with the coastal trough in the vicinity, at least until it becomes absorbed in the synoptic flow. As a result, expecting high temperatures around 50 across the far inland areas to the upper 50s at the coast Sunday. Very little temperature variation heading into Sunday night with ample cloud cover and weak return flow ahead of the cold front. Lastly, high temperatures Monday could approach 70F across the eastern two thirds of the forecast area in the relatively warm southwest flow prior to frontal passage. Highs around 70 are markedly higher than normal for this time of year (upper 50s). && .LONG TERM /TUESDAY THROUGH SATURDAY/... AS OF 230 PM Saturday...Progressive west-east flow aloft will continue across this part of the country with a fairly de-amplified pattern overall. H5 heights will slowly increase over the area late in the week with a trough to develop across the western United States and ridge in the east. During Tuesday an area of weak low pressure will develop off the NC coast with the first cold front moving through by Tuesday. Ample low-level moisture will maintain mostly cloudy skies through mid week with a continued chance of light showers. A better surge will arrive Wednesday night into Thursday as another area of cold high pressure ridges into the Carolinas from the Midwest. Drier conditions will take hold with below normal temperatures Thursday and Friday. Temperatures will begin to recover this weekend as return flow develops with high pressure shifting offshore. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 18Z...High confidence in VFR through tonight, but aviation conditions will deteriorate on Sunday. High pressure ridging into the area from the west will move overhead through tonight. This will continue SKC with light N/NW winds becoming near calm after sunset. Despite a clear and calm night, fog is not expected due to the very dry air, and VFR will persist into daybreak. On Sunday, winds will begin to increase to 5-10 kts from the east as a coastal trough develops offshore, creating slowly lowering clouds. Attm any restrictions are progged to hold off until just after this valid period, but at least SCT stratus/stratocu is expected at all terminals on Sunday. Extended Outlook...MVFR/-RA Sun evening with IFR Mon morning. VFR developing Mon. Periods of MVFR/-RA Mon night through Wednesday with IFR most likely during the morning hours. VFR Thursday. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 630 PM Saturday...No significant changes are needed to the forecast as 5 and 6 PM observations match closely with the previous forecast. Discussion from 300 PM follows... High pressure ridging to the east will deflect just to the NW of the local waters through tonight. SE of this high, a coastal trough will begin to sharpen in the offshore waters before drifting west on Sunday. The pressure gradient in the vicinity of these features remains light through Sunday morning, so winds will remain around 10 kts or less with slow veering from N to ENE late. These light winds and lack of a significant swell will keep wave heights just around 2 ft through the period. SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... As of 230 PM Saturday...Northeast flow around 10 knots Sunday morning will gradually veer to the east, then a southeast direction during Sunday afternoon with a coastal trough transitioning inland. The pressure gradient will increase by early Sunday evening and marginal Small Craft Advisory conditions are possible, mainly for the Cape Fear waters. The Small Craft Advisory conditions should be short-lived as the stronger pressure gradient shifts farther offshore by Monday morning. The improved maritime weather will persist into the afternoon with the overall flow veering to a west wind Monday afternoon. Light offshore winds are likely by Monday night. Seas will be highest as the winds peak in the wake of the coastal trough`s passage inland late Sunday afternoon into early Monday morning. Otherwise seas will be 4 ft or less Monday through Monday night. LONG TERM /TUESDAY THROUGH THURSDAY/... As of 230 PM Saturday...Weak low pressure is expected to form in the vicinity of the NC coast during Tuesday and push a weak cold front across the waters. A stronger surge is expected Wednesday night into Thursday with the passage of another front and sharp cold air advection in its wake. Brisk northerly flow will occur as a result during Thursday. Seas will range from around 4 ft on Tuesday and lower to around 3 ft during Wednesday. Seas will build again Wednesday night into Thursday in response to the surge.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DRH NEAR TERM...TRA SHORT TERM...SRP LONG TERM...SRP AVIATION...JDW

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