Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250518 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 115 AM EDT Thu May 25 2017 .SYNOPSIS...
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A cold front will cross the area late tonight through Thursday morning, followed by the passage of a strong upper level trough Thursday afternoon. Quiet and dry weather will return Friday. Warmer temperatures and chance for showers and storms will return over the weekend. A cold front will approach from the west on Memorial Day.
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&& .NEAR TERM /THROUGH THURSDAY NIGHT/...
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As of 915 PM Wednesday... A stacked low pressure system over the lower OH Valley will remain nearly stationary overnight. A s/w rotating around the base of the upper level low will usher a cold front west/southwest- east/northeast across central NC overnight. The initial band of convection that crossed the region late this afternoon/early evening has aided to stabilize the atmosphere somewhat though bulk effective shear is still strong enough to support organized convection in the form of broken bands. Thus expect a 20-30 mile band of convection along/ahead of the cold front overnight. Wind gusts 30-35 mph may occur with the stronger showers and storms along with briefly heavy rain. Partial clearing may occur behind the sfc front toward morning, especially across the sw half of the region. Though clouds will quickly fill back in later Thursday morning ahead of the upper level trough. Overnight temperatures should vary from the upper 50s/near 60 west to the mid 60s along and east of I-95. -WSS Thu/Thu night, as of 115 PM Wednesday: Another convectively active day expected on Thursday although with a different character and a more limited coverage and threat. A vigorous closed mid and upper-level low and upper-level trough axis over the eastern OH and TN valleys on Thursday morning will become negatively tilted and cross central NC between 18 and 00 UTC. At the surface, an initial cold front will extend north to south across the eastern Piedmont of NC at 12 UTC and then push east reaching the coast by 18 UTC as a second cold front reaches the Foothills of NC by 18 UTC and then the coastal region toward 00 UTC. The radar should be relatively quiet during the morning rush hour although some scattered showers are possible along the initial cold front that will be moving from the Piedmont into the Coastal Plain. Ahead of the front, dew points will range in the mid and even upper 60s supportive of convection. As the front exits, dew points will fall into the mid and upper 50s. Ahead of the approaching upper trough, large scale forcing for ascent will increase during the day Thursday. This will be supported by increasingly cold air aloft with 500 MB temperatures of -18 to -20 deg C which combined with steep low level lapse rates will lead to widespread cloudiness and the development of scattered showers and thunderstorms very late in the morning and into the afternoon. Cold air aloft resulting in suppressed freezing levels and an evolving but still robust wind field supporting shallow supercells, will support numerous cells with small hail and a few storms producing larger hail. As the previous shift noted, long and relatively straight forecast hodographs would lead to some splitting supercells and the potential for severe hail and damaging straight line winds. Limiting factor for severe weather will be the amount of instability while high cloud bases will reduce the tornado threat, they will support enhanced downburst winds. The greatest severe weather threat will be from 16 to 22Z, especially across the northern and western Piedmont. Convection will decrease from west to east during the late afternoon as the secondary cold front moves through and the air mass stabilizes. High temperatures will range in the lower 70s northwest to upper 70s southeast. Fair and dry conditions are expected Thursday night as heights rise and a surface high pressure extends into the region from the south. Low temperatures will range in the mid 50s to around 60. -Blaes
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&& .SHORT TERM /Friday through Friday night/...
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As of 115 AM Thursday... The mid level low over the Northeast early Fri will continue moving to the NE along the coast of the Canadian Maritimes through Fri night, with its trailing trough axis lifting NE away from NC Friday morning. Rising heights aloft and a drying/stabilizing air mass -- as agreed upon by the latest model runs -- supports plenty of sunshine with no pops. Low level thicknesses start the day well below normal but do start to recover in the afternoon, indicating highs just a tad under normal, 79-84. Fast mid level winds from the WNW Fri night will likely draw some high level moisture across the region, and we could see a little orographic enhancement of these high clouds, based on the forecast thermal and moisture profiles. Expect lows of 60-64. -GIH
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&& .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 125 PM Wednesday... In the wake of the strong, negatively-tilted trough axis forecast to exit the Middle Atlantic coast late Thu and Thu night, height rises aloft/ridging and associated subsidence, will sweep to the East Coast and yield dry and mild-warm conditions on Fri, as underlying surface high pressure settles across the southeastern U.S. A warm front will develop ewd across the central Appalachians and into the srn Middle Atlantic states (VA/NC) this weekend, though there remains uncertainty with respect to the precise location, particularly given probable modulation by convection/outflow. Nonetheless, there has been a consistent signal in model guidance in recent days that would suggest a couple of episodes of convection will likely develop along and north of the boundary Sat afternoon through Sun, before the front likely retreats nwd in advance of a weakening cold front forecast to settle into NC on Mon. Some storms may be severe, given relatively strong wind fields, and steep lapse rates related to a large plume of EML that will likely have overspread much of the sern U.S. and srn Middle Atlantic states, around the top of a progressive sub-tropical ridge along the Gulf coast. The next trough aloft will amplify and progress slowly across the central U.S. early-mid next week, with associated surface lows likely to lift across, and occlude over, the Great Lakes. Trailing fronts will consequently weaken as they drift east of the Appalachians and perhaps serve as a focus for primarily diurnal convection. Continued warm, in the 80s. && .AVIATION /00Z THURSDAY THROUGH TUESDAY/... As of 755 PM Wednesday... 24-Hour TAF period: Showers and storms continue to move through Central NC as of the 00Z issuance, lingering longest north and east of KRDU, which includes KRWI and surrounding areas. Light rain continues in and around KINT, KGSO, and KRDU. A lot of uncertainty still exists for the TAF period with respect to cigs and visbys. Largely expect visbys in the MVFR or VFR range with the showers, VFR elsewhere. Cigs are generally VFR, although they may fluctuate between VFR and IFR going from scattered to broken around 15 kft and 25 kft. Winds will be southerly, backing from SSE to SW through the period. Winds may briefly decrease to around 5 kts or so, but otherwise will be 8-12kts with gusts picking up Thursday morning. Additional showers and thunderstorms are possible during the day Thursday, accompanied by the usual reduced cigs and visbys. Looking ahead: Skies will clear out late Thursday night with a return to VFR conditions Friday and Saturday. There will be a chance for more convection late Saturday into early next week as a cold front approaches, however VFR conditions should dominate through Tuesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...WSS SHORT TERM...Hartfield LONG TERM...MWS AVIATION...KC

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