Area Forecast Discussion
Issued by NWS Wilmington, NC

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000 FXUS62 KILM 160731 AFDILM Area Forecast Discussion National Weather Service Wilmington NC 331 AM EDT Wed May 16 2018 .SYNOPSIS...
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Tropical moisture will continue to flow across the Carolinas through the weekend and into at least the first part of next week. A weak area of low pressure moving into the southern Appalachians may enhance the potential of heavy rainfall Thursday into early Friday. Bermuda high pressure will remain well offshore through the period.
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&& .NEAR TERM /THROUGH TONIGHT/...
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As of 300 AM Wednesday...At this point, pcpn over the adjacent Atl waters is not as widespread as earlier progs had indicated by this time. As a result, will knock down the initial coverage of the pcpn and associated QPF for the coastal areas. The cutoff mid-level low is progged to become an open trof that basically has it`s trof axis extending from Mobile Alabama southward across the central Gulf of Mexico to the Yucatan Peninsula. This positioning will continue to tap tropical moisture from the Gulf of Mexico and the western Caribbean and take it northeastward across the Southeast U.S. coast including the Eastern Carolinas and the ILM CWA. Anti-cyclonic flow around the Bermuda High, will tap the tropical Atlantic moisture, ie. the Bahamas and southward, and push it across the FA. Will have the days insolation to help fire up convection during the day. And at night, convection will fire up over the increasingly warmer Atl Waters and with progged trajectories taking it onshore during the pre-dawn hrs of both days, Wed morning and Thu morning. Any embedded weak mid-level s/w or vorts will further enhance the pcpn activity. This is definitely noted for later this Wed evening through the overnight Thu early morning time period. Have followed WPC QPF outline for the most part except placed additional QPF across the coastal Horry and Georgetown Counties, especially during the pre-dawn Thu hrs. As for temps, expect around a 10 degree diurnal range of temperatures this period as clouds and pcpn keep the days insolation in check.
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&& .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/...
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As of 300 AM Wednesday...The upper level low that sat over the northeastern Gulf of Mexico for the past several days should open up and lift north across the southern Appalachians with the approach of a shortwave from the west. The deep flow of tropical moisture originating from the Caribbean will continue across the eastern Carolinas, constrained by the Bermuda high well offshore and the trough to the west. Precipitable water values are still expected to climb to 1.8 to 1.9 inches Thursday, and could reach that magical 2.0 inch threshold Friday. According to the SPC sounding climatology website, this would be one of the earliest occurrences of 2.0 inch PW at CHS, and perhaps the earliest ever at MHX. Large scale ascent associated with the upper trough should keep the atmosphere uncapped. Forecast rain chances are 70-80 percent both Thursday and Friday, and 50-70 percent at night. Even with CAPE ranging from 500-1500 J/kg day and night, there should be a diurnal convective pattern apparent with rain chances highest inland during the afternoon/evening, and highest offshore and along the coast late night and in the mornings. Today through Friday night expect a widespread 1.5 to 2.0 inches of rain across the area, but with significant place-to- place variability. Severe weather does not appear to be a significant risk, but 20-25 kt of 0-6 km bulk shear may be just enough to induce some multicell organization with an enhanced risk of training storms and localized flooding rainfall, particularly on Thursday. Highs should only range from 80-83 both days, coolest on the beaches. Overnight lows should range from 68-72. Our local verification program shows the ECMWF has performed best with temperatures over the past few days, followed by the GFS, and then the NAM.
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&& .LONG TERM /SATURDAY THROUGH TUESDAY/... As of 300 PM Tuesday...It`s starting to appear that we transition seamlessly from one period of unsettled weather directly into another. The first will be the extension of widespread rain resulting from the Gulf system that will have been affecting the area since the short term period. And while this system will have an increasingly hard to discern surface reflection its persister weakness in the flow aloft to our west will lead to deep layer tropical moisture flux into the Carolinas. Previously it appeared that this feature (aloft) would lift out over the weekend and a trend towards drier weather may get underway. Now there is good agreement in guidance that another disturbance aloft drops into the weakness to our west and deep layer southerly flow is maintained through nearly the entire column depth. Pinpointing where this means best rain chances will set up is difficult. Guidance presently favoring coastal areas- have nudged forecast accordingly. Temperatures will be close to climatology by day but elevated at night due to widespread cloud cover. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 06Z...Latest 88d trends indicate pcpn to move onshore from Winyah Bay northward during the next several hrs. The most concentrated areas of showers will occur between Myrtle Beach to Cape Fear. Looking at MVFR with possible IFR conditions from any tstorm action across the coastal terminals. Should see additional pcpn with thunder to fill in across the Atlantic waters and push onshore during the Wed morning hours. For the LBT and FLO terminals this morning...a low stratus deck and partial reduction of vsby from fog remains possible but will not lean to heavy on the either one as a few of the onshore movement of showers will occasionally make it this far inland. Overall, this pcpn activity will translate inland later this morning and with the days insolation, convection will likely fill in across the inland terminals. The coastal terminals will see a relaxing of the onshore movement of pcpn other than occasional showers. By nightfall and thruout this evening, will see a reduction of pcpn coverage across all areas. This will be short-lived as pcpn over the Atl Waters begins to fire back up after 04Z and take aim for the coastal terminals. Extended Outlook...Periods of MVFR or IFR from lowered cigs/vsbys associated with tropical type showers and tstorms. Activity will be more numerous along the coast during the pre-dawn hours thru mid daytime morning each day. Then translate to the inland terminals from midday thru early evening each day. && .MARINE...
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NEAR TERM /THROUGH TONIGHT/... As of 300 AM Wednesday...SSE to S flow will slowly increase across the local waters this period in response to the slowly tightening of the sfc pg. Will increase wind speeds from 10-15 kt today to around 15 kt with gusts to 20 kt during tonight. The significant seas will also follow suit and slowly build thruout this period, reaching a solid 3 to 5 ft late tonight with 6 footers possible by daybreak Thu. The ESE ground swell at 8 to 9 second periods will be the dominant player within the seas spectrum. The increasing SSE-S flow and resulting wind-waves will combine with the ESE ground swell to push significant seas to the 6 ft SCA threshold by Thu morning. An SCA will likely be posted commencing Thu morning. Pcpn coverage of showers and embedded Tstorms is not as widespread over the local waters attm. Will continue the trend of the most areal coverage across the local waters occurring during the pre-dawn Wed hrs thru mid daytime Wed Morning followed by a reduction of pcpn coverage. This scene will play out again during the pre-dawn Thu hrs. The tropical rains will at times reduce VSBY to less than 1 NM. SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... As of 300 AM Wednesday...Bermuda high pressure will remain centered east of Bermuda this week. The Gulf disturbance that was being monitored for possible tropical development earlier in the week should be inland across southern AL/GA Thursday morning, then should move up through the southern Appalachians and into eastern KY Friday. As the disturbance makes its closest approach to our area Thursday, a pulse of stronger southerly winds is expected, with speeds increasing to nearly 20 knots sustained. Since there is already a long fetch in place from the Bahamas up to the Carolina coast, sea heights should build to 5-6 feet, and a Small Craft Advisory is being issued for Thursday. Winds should decrease to near 15 knots for Friday as the disturbance moves north. Waves of showers and thunderstorms are expected through the period as a stream of tropical moisture pulled out of the Caribbean crosses the area. Locally heavy rainfall will reduce visibility to 1-2 miles at times, and lightning will be a risk. LONG TERM /SATURDAY THROUGH SUNDAY/... As of 300 PM Tuesday...A large area of high pressure will be found well offshore through the period. To our west the pressure gradient will be somewhat poorly defined due to the slow moving feature aloft lifting north out of the Gulf of Mexico. This will keep conditions a bit shy of advisory levels and possibly also preclude SCEC as well since the coast-parallel winds may cap nearshore seas at 3ft even as offshore seas run 4-5ft.
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&& .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...Small Craft Advisory from noon Thursday to 9 PM EDT Friday for AMZ254-256. Small Craft Advisory from 8 AM Thursday to 9 PM EDT Friday for AMZ250-252. && $$ SYNOPSIS...TRA NEAR TERM...DCH SHORT TERM...TRA LONG TERM...MBB AVIATION...DCH

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