Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270818 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 417 AM EDT Fri May 27 2016 .SYNOPSIS...High pressure will extend across the area through today. A low pressure system developing off the Southeast coast will drift toward the northwest, approaching the Carolinas and Southeast coast over the weekend. && .NEAR TERM /through Saturday night/... As of 325 AM Friday... Today: Precip chances still appear small and limited to the far NW CWA. Offshore-centered high pressure will continue to ridge westward across the Carolinas through tonight, yielding a light southwesterly flow with no good opportunity for moisture advection into the area. Mid level heights will stay above normal over the area, despite the weak shear axis across the western Carolinas, which should trigger scattered convection over the higher terrain. This activity may drift into the Triad region late in the day, however the weak steering flow from the south will keep much of it west of the forecast area. Elsewhere, the warm and subsiding mid levels will result in minimal to no CAPE, despite the warm surface temps, and deep layer shear will be weak and insufficient to support any organized convection. Will hold onto an isolated late day pop over the far NW with dry weather elsewhere. Slightly above normal thicknesses combined with partly to mostly sunny skies favor highs of 84-88. Tonight: Baggy mid level low pressure over the Bahamas (southwest of the offshore anticyclone) will begin a slow drift toward the FL coast, with a band of vorticity on its NNE side (in tandem with a deepening surface low center) rotating about the low toward the SE coast. This still-light-but-increasing flow aloft from the ESE will draw in high clouds from the offshore convection, such that skies will trend toward fair or partly cloudy tonight from SE to NW. Low 60-65. Sat/Sat night: Rain chances are expected to increase as the baggy mid level low shifts ashore over FL/GA/SC, while the surface low located NNE of the low progresses further to the NW, likely reaching the Southeast coast by Sun morning. This low has the potential to take on some tropical characteristics (see products and bulletins from the National Hurricane Center regarding this possibility), but regardless of its nature, the increased influx of low level Atlantic moisture particularly into the SE and southern CWA along with improving (yet still unfocused) upper divergence and rising PW to 1.5-2.0" should lead to increasing rain chances, focused on the southern CWA, on Sat and especially Sat night. Will trend pops up gradually from SE to NW starting Sat, reaching likely in the SE and good chance NW by late Sat night, with skies trending toward mostly cloudy. While this system could generate gusty winds and some locally heavy rainfall near its center, given that most models keep its center near or just off the GA or southern SC coast through Sat night, such impacts could easily be suppressed well to our south. That said, we`ll be closely monitoring this system as we head into the long holiday weekend. Expect highs Sat 82-86 and lows Sat night 64-69. -GIH && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As of 345 AM Friday... Increasingly wet/stormy for the latter half of the weekend. A strong vorticity max parent to a complex mid to upper-level low now centered near the Bahamas will, according to a preferred GFS/ECMWF consensus, be "kicked" out of the mean low position --across the Carolinas-- by an upstream southern stream shortwave trough now over the Rio Grande. Meanwhile at the surface, the well- advertised low that the Air Force reserve Hurricane Hunter aircraft is scheduled to investigate this afternoon, is forecast to drift northwestward, to a position near the central SC coast by 12Z Mon. An inverted surface trough axis, likely in the form of a maritime tropical warm front, will extend northward from the low and bisect central NC. A deep southeasterly moisture plume, characterized by precipitable water values around 1.75 to 2 inches, will be directed into the Carolinas, between the mean upper low position near the Bahamas and a sub-tropical ridge centered near Bermuda. The presence of the moist axis will ripen the environment for numerous showers and storms, which will aided by forcing for ascent accompanying the mid-upper level vorticity max, and focused by low level convergence along the aforementioned inverted trough/warm front. Despite the presence of the warm front, the low level flow and associated shear are expected to remain weak, at least comparatively so for a nearby tropical cyclone environment, so now heightened risk of severe weather is anticipated. CLouds and convection will yield high temperatures around 80 degrees, albeit with noticeably higher humidity levels driven by upper 60s to around 70 degree surface dewpoints east of the warm front. Lows 65 to 70 degrees. && .LONG TERM /MONDAY THROUGH THURSDAY/...
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As of 410 AM Friday... Forecast confidence decreases by Memorial Day, at least with respect to the eventual position of the probable tropical or sub-tropical low near/over the Carolinas. Solutions from the past couple of runs of the ECMWF indicate the low will be near the south-central NC coast by 12Z Tue, while the same runs of the GFS support a more- southward solution, along the southern SC coast. In either case, the inverted surface trough/warm front will likely remain over central NC Mon and Mon night; and this feature will continue to serve as a focus for slow-moving showers and storms over at least the eastern two-thirds of the CWFA, which may begin to pose a flooding threat, partiuclarly after the previous 24-hr convection. Tue-Thu: Model differences grow through the middle of the week. GFS solutions depict a nearly stationary low over SC, and inverted surface trough extending northward over central NC, with a continued high probability of showers and storms through the end of the forecast period. On the other hand, ECMWF solutions suggest the low will be offshore the NC coast, with relatively dry conditions to the west/over central NC. Given the uncertainty and no clear preferred signal in model guidance, will simply trend the forecast toward climo, with slightly above avg PoP given the proximity of the remnant low. On a larger scale, a pattern change toward western CONUS ridging and a downstream trough west of the Appalachians, with an associated slow-moving /quasi-stationary/ surface frontal zone nearby, suggest conditions may be unsettled late next week and next weekend - continuing the recent run of above avg rainfall.
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&& .AVIATION /06Z Friday through Tuesday/... As of 210 AM Friday... High confidence in VFR conditions dominating central NC terminals today through tonight. A ridge of surface high pressure centered offshore east of VA/NC will continue to extend to the west and southwest, resulting in a light surface flow mainly from the SW over central NC, and sufficiently dry low levels to preclude fog development. Meanwhile, dry and sinking air in the mid levels will suppress most cloud development, with any clouds likely to be based at 4-6 kft AGL. Pockets of shallow ground fog are possible near RWI this morning (due in part to the proximity of water) between 08Z and 12Z, however the latest guidance shows a low enough potential to preclude a mention in the TAF at this time. An isolated storm is possible near INT/GSO late this afternoon or early evening, but coverage will be too low to include in these TAFs. Looking beyond 06Z early Sat morning: VFR conditions are likely to hold through at least early afternoon Sat. Clouds will then thicken and lower from SE to NW -- affecting FAY and RWI first -- starting late Sat, as an offshore low pressure area tracks NW toward the Southeast states. Areas of MVFR/IFR conditions in rain and isolated storms are expected to spread into the FAY vicinity Sat evening before expanding across all central NC terminals late Sat night, continuing into Sun. Areas of sub-vfr fog are possible Sun night and Mon night, with mostly VFR conditions during the day Mon and Tue, however the forecast confidence drops dramatically beyond Sun regarding the path of the offshore low... so aviation interests should monitor the latest forecasts closely over the long holiday weekend. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...26 LONG TERM...26 AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.