869 FXUS62 KILM 122123 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 523 PM EDT Sun Mar 12 2017 .SYNOPSIS... A trough of low pressure off the Georgia coast will develop into a low pressure system Monday afternoon, then will move northward along the East Coast Tuesday and Wednesday. Canadian high pressure advancing across the Midwest will push very cold air into the Carolinas, with hard freezes possible Wednesday, Thursday and even Friday mornings. && .NEAR TERM /THROUGH MONDAY/... As of 520 PM Sunday...Biggest change with this update was to issue a Freeze Warning for roughly the northwestern half of the forecast area (north of a line from Lake City and Marion to Whiteville and Burgaw) for tonight. Temperatures should slip to 30-32 degrees across this area after midnight. Unfortunately for local farmers tonight will not be the worst weather of this week; that's looking like Wednesday and Thursday nights when hard freezes will likely drop lows deep into the 20s. Satellite shows the clearing line advancing southwestward at around 15 mph across southern NC. Linear motion extrapolation brings clearing into Wilmington around 8 PM and Florence between 10 and 11 PM. Observed temperatures at 5 PM are running well below the GFS or NAM MOS guidance, so I have used a blend of raw RAP/HRRR/NAM models to construct hourly temperature curves through the night. The speed at which temperatures fall overnight will be strongly determined by how quickly skies clear out. Synoptic models suggest late tonight moisture will again increase with low clouds shifting back onshore, and this may cause temperatures to rise several degrees. Discussion from 300 PM follows... Our late season winter event has wound down. But in its wake has been left such an error in temperature guidance that making frost/freeze decisions for the overnight hours difficult at best. Even though the LAV has finally started initializing better than the MET/MAV it too wants to show rising temps through the evening and that just seems unlikely based upon upstream observations. Guidance also seems to be clearing out the cloudiness way to quickly this evening, further arguing against any temperature rebound of more than a degree or two (despite the warm advection going on aloft). && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 330 PM Sunday...Isolated to scattered showers will gradually taper off across the area Monday night into early Tuesday morning as a coastal sfc low gradually moves up and away from the Carolina coast. Do not anticipate any wintry precipitation as temperatures will remain above freezing, with overnight lows in the mid 30's inland to lower 40's along the coast. As the system continues to move northeastward and expand into the northeast, strengthening from a mid-level shortwave will allow for a cold Canadian airmass to infiltrate in behind the system into the Carolinas on Tuesday. With dry conditions expected Tuesday and Tuesday night, high temperatures will warm into the mid to upper 50s during the day on Tuesday, but into the night hours, temperatures will drop to around or below freezing, with the upper 20's inland and lower 30's along the coast. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 330 AM Sunday...Winter is not quite over yet. The mild to warm temperatures experienced much of this winter season will be just a memory when compared to this period and week. Agricultural Interests will be tested this period with daily lows Wed, Thu and Fri mornings in the 20s to around 32 at the immediate coast. This is 15 to 20 degrees below normal. Daily highs will see temps struggling into the 40s Wed and Thu with 50s Fri and around 60 Sat. This too is 15 to 20 degrees below the norm. Wed and Thu. The longwave pattern aloft will have a nicely amplified upper trof affecting nearly the eastern half of the United States. This pattern will result in very cold air with Arctic origins plunging southeastward across the Carolinas from central Canada. The upper trof axis will transition to just off the coast from the Carolinas this period, resulting in fortunately a dry forecast but again very cold. Wind chill readings will run in the teens at times with winds staying active Wed into Thu. By late Thu thru Fri, winds will finally drop off but the cold temps will continue. Saturday may see a rebound of temps back to normal with the threat of light liquid pcpn. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... AS OF 18Z...Dry air pushing in strongly from the NW, shutting off precipitation at the coastal terminals over the next hour or two. Other than some lingering cirrus clouds the rest of the afternoon will see decreasing clouds and generally VFR. Clouds will return overnight ahead of the next system, first along the coast then inland. Flight category reduction will be minimal, but should decrease soon after the TAF period as low pressure develops off our coast later Monday. Extended outlook...MVFR/IFR conditions are possible in rain and low ceilings late Monday afternoon through Monday night. VFR conditions should develop by late Tuesday morning and persist through Thursday. && .MARINE... NEAR TERM /THROUGH MONDAY/... As of 520 PM Sunday...No significant changes are needed to the marine forecast with this update. Stronger NE winds are still expected to develop overnight with deteriorating seas as well. Discussion from 300 PM follows... Pinched NE gradient to continue through the period as will Small Craft Advisory as the area remains in between a very chilly high wedged up east of the Appalachians and a weak trough off the coast. As this trough closes off into a low late Monday the wind will become lighter and turn counterclockwise in direction. The Advisory continues however as conditions will go downhill quickly following its passage. SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 330 PM Sunday...Expect Small Craft Advisory to continue across all waters late into Monday night, thereafter continuing across AMZ- 252 and AMZ-250 through the remainder of the forecast period as increased wave heights continue. Increased wave energy will continue through the period as a coastal low offshore slowly pushes farther away from the coast. Seas around 6 to 8 ft through late Monday will drop to 4 ft across the southern waters, while 4 to 6 fters continue across the northern waters. Northeast winds around 15 to 20 kts will persist late, becoming southwest into Tuesday morning, with sustained winds around 15 kts. LONG TERM /WEDNESDAY THROUGH FRIDAY/... As of 330 AM Sunday...SCEC to borderline SCA will occur Wed diminishing to SCEC or lower Thu and even lower speeds by Fri. The one constant thing this 3 day period will be wind directions from the NW thruout this time-line. During Fri, the center of high pressure will drop southward across the waters resulting in wind speeds finally dropping into the single digits. With an offshore NW wind direction, significant Seas will range from 1 to 3 ft nearshore ie. 0 to 10 nm out, and 3 to 5 ft outer waters ie. 10 to 20 nm out. By and during Fri, seas will further drop to 1 to 3 ft thruout. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Freeze Warning from midnight tonight to 9 AM EDT Monday for SCZ017-023-024-032-033. NC...Freeze Warning from midnight tonight to 9 AM EDT Monday for NCZ087-096-099-105. MARINE...Small Craft Advisory until 2 AM EDT Tuesday for AMZ254-256. Small Craft Advisory until 8 AM EDT Tuesday for AMZ250-252. && $$ SYNOPSIS...TRA NEAR TERM...TRA/MBB SHORT TERM...SGL LONG TERM...DCH AVIATION...MBB