Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 212344 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 744 PM EDT Tue Mar 21 2017 .SYNOPSIS... A cold front will move through the Carolinas late tonight, accompanied by scattered showers and thunderstorms. Cold Canadian high pressure will build southward from the Great Lakes Wednesday night through Thursday night, perhaps bringing freezing temperatures to some inland locations. The high will move offshore Friday with a warming trend expected over the weekend, along with an increasing chance of showers or thunderstorms by Sunday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... As of 300 PM Tuesday...Deep northwest flow this afternoon will persist into the overnight hours. A strong shortwave will move southeast into the region overnight, with showers and thunderstorms anticipated ahead of this feature. Surface based instability will be diminishing before the wave reaches the area. Forecast soundings and cross sections suggest the lowest 3k-5k ft could be quite stable by the time waning convection moves into the forecast area, sometime after 01Z. Low level stability and the lack of any low level jet lessen the potential for damaging wind associated with convection, but the presence of elevated CAPE and cold temperatures aloft suggests hail will be possible, particularly for portions of interior SC. Elevated instability in this area is highest and the strongest PVA ahead of the shortwave will be found here. Despite several favorable factors think overall coverage of strong/severe storms will be limited. Showers and, for the first part of the overnight period, thunderstorms will be fairly widespread and most areas are likely to pick up anywhere from 0.10"-0.25" before the shortwave exits and the strongest activity moves offshore. The shortwave drags a cold front across the area overnight with northerly flow developing early Wed morning as Canadian high starts building in from the northwest. Low level moisture will linger into mid-late morning Wed, especially along the coast but by midday cooler and drier air will be spreading over the region. Highs will end up a little below climo, upper 50s to lower 60s. Afternoon temperatures may trend down a little earlier than usual as cold advection picks up. Cold advection in the afternoon may also lead to breezy conditions developing after midday and continuing through sunset. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...The question for this period will be...how cold will we get? Wed night will experience better CAA while Thurs night will be the better radiational cooling night. There will be more of a north to south gradient as high pressure builds in from the north as the center shifts east toward the NC/VA coast by Thurs eve and then farther off the coast by Fri morning. This will generally produce a shift in winds from the N to the NE by Thurs and around to the E by Thurs night. The on shore component to the flow will limit the dewpoint temps from dropping by Thurs evening. Up until then, there will be plenty of cold and dry air pushing south as high pressure builds in behind cold front. A deep NW to N flow will maintain pcp water values below .25 inches through Wed night into Thurs morning. Dewpoint temps will drop to the teens on our northern border while the SC coast will see the mid 20s by Thurs aftn. This cool and dry air mass will set the stage for possible freezing temps early Thurs morning and possibly again early Fri morning. 850 temps will start out around 1 to 2 C Wed eve, down from near 13C early Wed. There will be another gradual drop through Thurs down to near 0C as ridge begins to sharpen to the west of area enhancing the CAA. There may be some mid to high clouds spilling over the ridge in a more westerly flow in the low to mid levels through Thurs into Thurs night. The timing may actually act to keep day time high temps slightly lower on Thurs but may help to keep temps a little warmer Thurs night across SW to W portions of area. Overall expect mainly clear skies both Wed and Thurs night with temps down to 30 to 35 over most of NC Wed night and 35 to 40 over SC and along the coast in brisk northerly winds. Thurs temps should rebound into the 50s as CAA battles against the sunshine which may be blocked at times by the clouds. By Thurs night, mainly clear skies will combine with calm winds to produce temps possibly near freezing over spots in Pender and Bladen county while other places should be between 35 and 40 degrees. With such light winds through the lower levels, do not expect much moisture return Thurs night but dewpoint temps will make it back up to 30 or so by daybreak Fri in the coldest spots. This will help temps from plummeting too much Thurs night. Will hold off on any Freeze Watch for now for Wed night because it remains very borderline. && .LONG TERM /FRIDAY THROUGH TUESDAY/... As of 300 AM Tuesday...High pressure off the East Coast should produce a warming trend through the period. Highs in the 70s and lows in the 50s are expected through the period. The best chance of showers or t-storms will probably be late Sunday as a weakening upper system shears out through the Great Lakes but drags a ribbon of moisture and modest lift through the Carolinas. It`s getting close to that time of year where daytime instability could become a large enough factor to pop some showers or t-storms, and Sunday might be our first bout of that for the year. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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As of 00Z...VFR conditions will prevail through mid to late this evening. There-after 2 wx features will combine to produce possible MVFR/IFR conditions from convection later this evening and overnight. The 1st feature will be a cold frontal boundary dropping southward thru the area by daybreak Wed. And the 2nd feature, a mid-level s/w trof moving ESE and across portions of the area by mid to late pre-dawn Wed hrs. Low ceilings will remain possible for atleast several hrs after the CFP along with light showers or drizzle. By midday, expect VFR conditions as ceilings further lift as a drier airmass infiltrates the area. A tightened sfc pg combined with CAA will produce gusty N to NNE winds at 15 to 25 kt from mid daytime morning Wed thru late afternoon Wed with the gustiness dissipating after sunset Wed. Extended outlook...VFR expected through the period. The exception will be possible MVFR conditions late Sunday due to a CFP.
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&& .MARINE... NEAR TERM /THROUGH WEDNESDAY/... As of 300 PM Tuesday...Modest southwest flow continues this afternoon and evening ahead of shortwave and associated surface cold front dropping in from the northwest. Speeds may briefly rise into the 15 to 20 kt range just prior to the front reaching the coast later this evening. Wind speeds will drop with arrival of the front, becoming west-northwest once it passes. Initially the gradient behind the front is weak and offshore flow will be light, but shortly after daybreak Wed northerly flow will start increasing. Cold advection and tight gradient could result in north to northeast flow of 20 to 25 kt developing by Wed afternoon and continuing through the end of the period. Seas 3 to 5 ft this afternoon may briefly drop to 2 to 4 ft overnight as winds shift and decrease in speed. Reduction in seas will be short lived with increasing northerly flow building seas to 4 to 6 ft Wed afternoon. Based on this have decided to raise a SCA for all zones starting Wed afternoon and continuing through the end of the period. SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/... As of 300 PM Tuesday...Strong northerly winds will continue through Wed night into Thurs as high pressure builds south behind cold front. A Small Craft Advisory will remain in effect into Thurs afternoon, at which time the winds will diminish. The center of the high will remain north of the waters as it shifts east toward the NC/VA border by Thurs night and farther off shore by Fri morning. This will produce a shift in winds from N-NE to NE-E through the period. Seas will be up to 5 to 8 ft overnight Wed in N-NE winds up to 25 to 30 kts. Winds and seas will drop below SCA thresholds by Thurs aftn dropping down near 3 ft in a light easterly flow by Fri morning. LONG TERM /FRIDAY THROUGH SATURDAY/... As of 300 AM Tuesday...Canadian high pressure off the East Coast will weaken through the period, assuming a position only a bit farther north than the typical summertime Bermuda High by Saturday. Light easterly winds Friday should become more southerly Saturday. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory from 2 PM Wednesday to 5 PM EDT Thursday for AMZ250-252-254-256. && $$ SYNOPSIS...RGZ NEAR TERM...III SHORT TERM...RGZ LONG TERM...TRA AVIATION...DCH

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