Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 201018 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 618 AM EDT Mon Mar 20 2017 .SYNOPSIS... High pressure across the Carolinas this morning will settle across Florida tonight. A cold front approaching from the north will move across the area Wednesday morning. Canadian high pressure building southward will provide chilly conditions Thursday with the potential of frost or another freeze. The high will move offshore Thursday night with moderating temperatures expected for the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 300 AM Monday...Nearly ideal radiational cooling ongoing early this morning, and temps are falling faster than any available guidance can depict. Many sites are 34 or less as of 3am, with a few of the typically colder spots, Back Island RAWS, Conway AWOS, Supply RAWS, at or below freezing. Despite the colder temps, do not expect a widespread freeze event, and issuing a freeze warning at this time would do little to help agricultural interests anyway. Have shown mins tonight falling to 32 or less in several spots, with widespread sub-35 expected, and the ongoing frost advisory continues. This means you can expect some frost on those eggs this morning if you try to balance them - the vernal equinox occurs at 6:28 AM! The synoptic pattern responsible for this cold night is a large area of high pressure ridging down from the Great Lakes, combined with dry NW flow through much of the column upstream of a closed mid- level low off New England. This flow will allow the surface high to gradually shift SE today and re-center across the Gulf Coast and into the western Atlantic. With dry W/NW flow persisting aloft, abundant sunshine and a slowly rising thicknesses will allow temps to recover close to seasonable norms this aftn. Highs will range from the low 60s in the vicinity of Cape Fear, to the upper 60s along the South Santee and in the Pee Dee. This is on the warm side of the guidance and in some places even a bit above the warmest numbers, as strong March sunshine combined with downslope flow should warm the area nicely from the cold morning lows. A cold front will begin to approach from the north tonight as the high shifts further to the SE, and between these two features SW winds will begin to increase. This will drive warm advection tonight, which will work in tandem with increasing cloudiness advecting southward to insulate the surface and create a much warmer night. Lows by Tuesday morning will fall only to around 50 at the immediate coast, mid to upr 40s elsewhere. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...Surface high pressure over Florida and the Bahamas will weaken Tuesday as the upper level ridging across the Gulf gets beaten down by a developing longwave trough over the eastern U.S. A surface cold front across the Mid-Atlantic states will slip southward into North Carolina Tuesday night and into our area just before daybreak on Wednesday. The spread in model timing with this front is still a bit larger than we`d normally see at 60 hours out. The 00z GFS is faster than the 00z ECMWF or NAM despite similar timing of the 500 mb shortwaves embedded within the developing longwave trough. I favor the slower ECMWF/NAM timing. There is not a great inflow of moisture into this system on Tuesday. The flow aloft is generally westerly and 850/700 mb moisture appears to arrive on a circuitous route from the Texas and then eastward across Arkansas and Tennessee. For this reason I am not keen on bringing PoPs into the forecast until Tuesday evening and night when significant lift develops in association with a train of shortwave disturbances. Lapse rates appear steep enough aloft to continue to mention thunder in the forecast as well. The cold front will push through from north to south Wednesday morning. Shallow cold advection initially extending only up to around 4000 feet AGL will probably create persistent clouds and potentially some patchy light rain or sprinkles during the day. Drier air should arrive by Wednesday evening with clearing skies and continued cold advection. Unfortunately for farmers or just those of us ready to get our spring gardens planted, another freeze or frost event is possible late Wednesday night, especially across SE North Carolina. && .LONG TERM /THURSDAY THROUGH SUNDAY/... As of 300 AM Monday...Canadian high pressure over the eastern Great Lakes Thursday morning will move off the Mid-Atlantic coast Thursday night and farther offshore Friday. After a chilly day Thursday with highs only in the 50s we could see one last night of frost or freeze conditions Thursday night with light winds in the vicinity of the high. By Friday return flow around the high should begin to modify the airmass with highs returning to the 70s by Saturday. The next synoptic frontal system should begin to move across the Southeast states this weekend, perhaps spreading showers and t-storms into the Carolinas Saturday, but with better chances by Sunday. SPC, in their extended range convective outlook, mentions weak instability across the warm sector including the Carolinas but with too much uncertainty to consider a severe weather risk for now. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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As of 12Z...VFR conditions will continue over the next 24 hours as surface high pressure sinks from the Carolinas down into Florida. Surface winds will back from northerly to southwesterly with speeds generally under 10 knots. Extended outlook...VFR expected through the period except for possible MVFR/IFR conditions from low ceilings and convection ahead of the next cold front Tuesday night into Wednesday.
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&& .MARINE... NEAR TERM /THROUGH TONIGHT/... As of 300 AM Monday...Expansive high pressure will build across the waters today before re-centering to the S/SE tonight. This will persist a weak gradient through the day, so this mornings north winds of 10-15 kts will ease quickly to become light and variable through the aftn before rising again to 10-15kts from the SW tonight. An easterly swell will remain in the wave spectrum today at around 11 sec, and will likely be the dominant wave group this aftn during the period of lightest winds. However, this will become increasingly masked by an amplifying SW 5 sec wave tonight. Seas of 2-4 ft this morning and again tonight will bookend otherwise more placid wave heights of 1-3 ft much of the aftn. SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... As of 300 AM Monday...High pressure over Florida and the Bahamas will dissipate Tuesday as a cold front moves south across the Mid-Atlantic states and into North Carolina Tuesday night. Admittedly models still have a 6-to-8 hour spread in timing of when the front will actually arrive, ranging from midnight (00z GFS) to around sunrise Wednesday morning (00z ECMWF and NAM). I am still favoring the later timing and my forecast shows southwest winds Tuesday continuing through Tuesday night. Once the front does go through Wednesday morning, strong northeasterly winds will develop with a Small Craft Advisory almost certainly needed for Wednesday night, if not beginning during the day on Wednesday. LONG TERM /THURSDAY THROUGH FRIDAY/... As of 300 AM Monday...Canadian high pressure over the Great Lakes on Thursday will sink southeastward to the Virginia coast Thursday night, then will move offshore Friday. Clockwise winds blowing around the high will probably maintain Small Craft Advisory conditions for most of Thursday, if not Thursday night. By Friday a weaker pressure gradient on the west side of the high should allow veering winds to diminish to less than 15 knots. A significant east to northeast backswell is expected to continue through Friday due to the large area of strong winds covering the western and central Atlantic around the periphery of this high. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...Frost Advisory until 8 AM EDT this morning for SCZ017-023-024. NC...Frost Advisory until 8 AM EDT this morning for NCZ087-096-099- 105-107-109. MARINE...None. && $$ SYNOPSIS...TRA NEAR TERM...JDW SHORT TERM...TRA LONG TERM...TRA AVIATION...TRA is the U.S. government's official web portal to all federal, state and local government web resources and services.