Area Forecast Discussion
Issued by NWS Wilmington, NC

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561 FXUS62 KILM 160604 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 104 AM EST Thu Nov 16 2017 .SYNOPSIS... Canadian high pressure to our north will continue to bring near seasonable temperatures and dry conditions following a weak cold frontal passage by Thu morning. A brief cool down on Friday will be followed by mild and breezy conditions on Saturday ahead of an approaching strong cold front. This cold front will bring a small chance of showers before passing off the Carolina Coasts by early Sunday. Cool and dry Canadian high pressure will build back over the Carolinas, bringing a chance for freezing temperatures and/or frost both Monday and/or Tuesday mornings of next week. The high will migrate off the Carolina coasts by the middle of next week bringing a return to milder temperatures. && .NEAR TERM /THROUGH TODAY/... As of 745 PM Wednesday...A mid-level s/w trof within relatively zonal flow aloft, will push across the area late tonight. It will help push a cold front across the area and off the Carolina coasts around daybreak Thu. Scattered pcpn along the front at the moment will dissipate after pushing across the Appalachians. Any leftover cloudiness will more likely scour out by the time it reaches the Carolina Coasts due to W to WNW downslope flow aloft. The stratocu deck from off the Atlantic continues to partially cover the Cape Fear Region and northward. With flow at all levels becoming W to NW overnight into daytime Thu, the low level stratocu deck will both scour out as it gets pushed back off the NC Coast later tonight. Some tweaking of temps applied, mainly to hourly temps that are affected by the low cloud deck. But the overall min fcst still looks aok. Previous........................................................ As of 300 PM Wednesday...High pressure extending down from the north will weaken as a shortwave pushes the tail end of cold front toward the Carolinas from the NW through tonight. The low to mid level flow will back around to W-NW by this evening. Moisture profiles and sounding data show main layer of increased moisture from 7k-12k ft for a few hours overnight. Overall, expect a slight uptick in mainly mid to high level clouds as shortwave moves through overnight tonight but without much moisture return in the low levels, the front will go through mostly unnoticed with just a reinforcement of dry high pressure into Thurs. Temps tonight will be a few degrees above last night as clouds help prevent ideal radiational cooling. The increased westerly downslope component to the flow and plenty of sunshine on Thurs will produce temps in the mid 60s. The deeper cooler northerly flow will come later on Thursday as H5 trough lifts north and east with reinforcing shot of cool Canadian high pressure. && .SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...Cold front will be offshore to start the period leaving cool and dry weather in its wake. NW flow aloft combined with dry canadian surface high pressure building southward, PWATs will fall to around 0.25 inches during Friday, leaving clear sky conditions and bright sunshine. Cool advection and the airmass having Canadian origin will keep temps below climo Friday, rising only to around 60 in the shallow cold air despite full sunshine. Mid- level flow becomes more zonal into Friday night pushing the surface high offshore and allowing warm advection to develop late. This will manifest as increasing SW winds and moisture return, with advective stratocu possible along the coast Friday night. This flow will keep mins in the low 40s Friday night, a few degrees warmer than Thursday night which will feature better radiational cooling. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 300 PM Wednesday...The Subtropical Ridge will get suppressed deep into southern Mexico and the Caribbean as a trough develops across eastern North America this weekend. The key feature will be a shortwave moving across the area Sunday morning, preceded by a wave of clouds and light showers Saturday night. This system will be followed up by an airmass equally cold to the one we had back on November 11th which has the potential to bring freezing temperatures to portions of the eastern Carolinas Monday morning. Saturday looks to be a wonderful day with a brief warmup to above- normal temperatures expected. 850 mb temps surging to around +11C should equate to highs in the 72-74 range, the warmest day since back on November 7th. As the trough and a surface cold front approach from the west Saturday Night, a narrow band of moisture ahead of the front should yield scattered showers mainly after midnight. The flow is deeply westerly with no Gulf or Atlantic inflow, so even spots that pick up rain will likely only get a few hundredths of an inch total. After frontal cloudiness clears out during the day Sunday, insolation will be offset by cold advection and highs should only reach 60. We`re forecasting lows in the lower 30s as far south as Florence, Marion, Whiteville, and Burgaw Sunday Night as 850 mb temps plunge to around +1C. Up through Monday all the models were in great agreement with each other. Differences become apparent Monday night with regards to how quickly the incoming Canadian High moves across the Carolinas. The 00Z and 12Z ECMWF are both much faster moving the high across and offshore Monday night and Tuesday compared to the GFS. WPC prefers the ECMWF and its ensemble mean to the 06Z/12Z GFS, therefore I have altered our forecast with this in mind. A faster return flow behind the departing high pressure should make Monday night`s lows several degrees warmer than our previous forecast, and will lead to a faster return of clouds as Atlantic moisture increases Tuesday-Wednesday. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 06Z...Mid-level cloud associated with a weak disturbance aloft will exit to the east around daybreak. High pressure building in from the northwest today with a dry cold front passing late in the day. Light northwest winds this afternoon will become northerly overnight and increase as cold surge arrives. VFR conditions will prevail through the TAF period. Extended Outlook...VFR with a chance of showers and possible MVFR/SHRA Saturday into Sunday.
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&& .MARINE... NEAR TERM /THROUGH THURSDAY/... As of 800 PM Wednesday...The sfc pg will slightly tighten during this evening and overnight, ahead of an approaching cold front. This will yield Northerly winds at 10 kt, becoming NNW-NW 10 to 15 kt after the cold frontal passage Thu morning and hold at these speeds thruout the day on Thu. Significant seas will run 1 to 3 ft with a few 4 footers possible across the outer waters off Cape Fear. Due to the NW to NNW wind directions, the wind wave, 3 to 5 second periods, portion of the significant seas will be limited due to fetch constraints. This will leave a 2 to 3 foot Easterly ground swell at 8 to occasionally 10 second periods the more dominant player within the sig. seas. Previous................................................... As of 300 PM Wednesday...High pressure extending down into the waters from the north will shift east and weaken through tonight as a weak and dry cold front approaches from the NW. Overall expect winds to lighten and back to the NW by this evening. Winds will remain NW between 10 to 15 kt through Thursday. Seas will subside a bit more basically running 2 to 4 ft through Thurs. SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/... As of 300 PM Wednesday...Cold front offshore to start the period will leave winds increasing to 15-20 kts while veering from NW to N through Friday morning. These winds will veer further to the NE but weaken on Friday as high pressure builds southward towards the waters, becoming light and variable briefly before shifting around to the S at 10 kts or less as the high shifts offshore Friday night. Seas will be nearly entirely wind-driven this period, driving amplitudes to 3-5 ft Thursday night into Friday on the gusty north winds, before falling back slowly to around 2 ft Friday night. LONG TERM /SATURDAY THROUGH MONDAY/... As of 300 PM Wednesday...Southwesterly winds will increase during the day Saturday and especially Saturday night ahead of o occasionally 15 kt late tonight.a cold front which should move offshore before daybreak Sunday. Behind this front, winds will shift northerly with cool Canadian air spreading across the area. Small Craft Advisory conditions may be met beginning late Saturday afternoon through Sunday morning, with breezy but lighter offshore winds continuing into Sunday night. Winds should veer northeasterly on Monday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...DCH NEAR TERM...DCH SHORT TERM...JDW LONG TERM...TRA AVIATION...III

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