Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 270026 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 825 PM EDT Fri May 26 2017 .SYNOPSIS... A weak trough will extend down through western and central North Carolina. An upper level disturbance will cross the region late Saturday through Saturday night, followed by another disturbance Sunday afternoon. && .NEAR TERM /OVERNIGHT/... As of 825 PM EDT Friday... A rare pristine/unmodified elevated mixed layer characterized by H7- H5 lapse rates on the order of 8.5-9.0 C/km will advect eastward across the southern Appalachians into the Carolinas tonight. Marginal nocturnal destabilization will occur as mid-level lapse rates become nearly dry-adiabatic, however, poor low-level moisture will maintain considerable CIN and preclude significant destabilization through 12Z Sat. With clear skies and calm winds, expect overnight lows ranging from the upper 50s to lower 60s, warmest in the S/SW. Severe Potential on Saturday: The aforementioned EML will set the stage for strong to extreme diurnal destabilization Sat afternoon in the N/NW Piedmont as rich low-level moisture advects beneath it from the W/SW. With central NC firmly embedded in the westerlies and equilibrium levels approaching ~13km, effective deep-layer shear (0- 8km) will likely reach 40-45 knots Sat aft/eve. Diurnal heating and low-level moisture advection are expected to erode the CAP across the N/NW Piedmont by late afternoon, however, significant uncertainty persists with regard to whether or not convection will develop since the magnitude/timing of forcing will highly depend on the evolution of upstream convection overnight and early Sat. The latest convection allowing models suggest at least isolated development will occur north of Hwy 64 late Sat aft/eve. If deep convection develops over or propagates into central NC late Sat afternoon, thermodynamic/kinematic profiles would support intense supercells capable of producing destructive hail (1.75-2.75") and wind (65-75 mph). -Vincent && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 350 PM Friday... Low amplitude shortwave disturbances riding atop the flat subtropical ridge in place across the southern U.S. will set the stage for scattered upstream convection to move into the area within a west-southwesterly WAA belt spreading east into the southern Appalachians late tonight/early tomorrow morning and then into central NC on Saturday. The convection should align closely to a wavy west-east frontal zone that will initially push east into VA during the afternoon, and then gradually sag south into central NC during the evening and overnight, likely aided by the expected convective and associated outflow. While an EML plume advecting into the area may help to bolster destabilization across the area, it may also serve to limit convective coverage especially south of US 1. Will keep a good/high chance across the far north with only slight chance pops across the south, with a decrease in pops with cooling after sunset. A strong mid-level wind field will result in favorable deep layer shear of 30 to 35 kts, along with moderate instability to support a cluster or two of severe storms capable of producing large hail and damaging straight-line winds, mainly along and north of HWY 64. Warming H8 temperatures to 15 C tomorrow(+ 5C from Friday) with a corresponding 20 meter rise in low-level thicknesses to 1420 meters will support a quick return to above normal temperatures. Highs in the mid to upper 80s north to lower 90s south. Lows tomorrow night in the mid to upper 60s with some patchy fog possible where any heavy rain falls. && .LONG TERM /Sunday through Friday/... As of 300 PM Friday... A short wave trough over the TN valley Sunday morning will move east and across the Carolinas by late day. Scattered showers/tstms are expected along and ahead of it, developing over the mountains around mid-day and moving east across our cwa during the late afternoon into early evening. With 2000+ J/kg cape and 40+ kt of deep layer shear forecast in the models, the environment would appear to support at least isolated strong to severe tstms. Given the position of an old boundary along and north of hwy 64, look for the best chance for such activity to be across the northern half of our CWA. Short wave ridging behind the aforementioned short wave will provide a break in the weather Sunday night into Monday morning, but the next short wave moving through the longwave trough centered over the Great Lakes will move across the Carolinas late day Monday into Monday night, helping to push a weakening cold front across our area. This system will provide the next chance for showers and tstms Monday afternoon through Monday night. For the rest of the long term period, will keep pops near or above climo each day as the aforementioned cold front will stall across the region and a series of mid level short waves embedded in the broad cyclonic flow move across the region. Above normal temps forecast through the period. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 825 PM Friday... Weak high pressure south of the area will produce VFR conditions for the 24 hour TAF period. A frontal zone will be developing north of the area on Saturday, and there could be a few showers and storms develop across the northern tier of central NC, possibly impacting the INT/GSO/RDU sites towards 21Z late tomorrow afternoon. West/southwest winds will pick up a bit tomorrow, with 10 knots expected by 16Z with gusts to 20 knots. Outlook: A series of upper level disturbances along the frontal zone will nudge the front south into the area Saturday night. There will thus be a chance of showers and mainly late day storms on Sunday, and again on Monday through Wednesday as a cold front slowly approaches from the west and potentially stalls over the area.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...BV SHORT TERM...CBL/BV LONG AVIATION...mlm is the U.S. government's official web portal to all federal, state and local government web resources and services.