Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250627 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 227 AM EDT Thu May 25 2017 .SYNOPSIS...
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A cold front will cross the area this morning, followed by the passage of a strong upper level trough this 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/... 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 && .SHORT TERM /Friday through Friday night/... 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 && .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 /06Z THURSDAY THROUGH TUESDAY/...
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As of 220 AM Thursday... A band of strong storms now extending from near HBI to RCZ to FLO will sweep northeastward and affect RDU, FAY, and RWI during the next few hours. Small hail and wind gusts up to 40 kts will accompany the storms. Otherwise, IFR-MVFR ceilings will gradually lift and scatter from west to east through 12Z, as a lead cold/occluded front and following drier air in the low levels spreads east across central NC this morning. Scattered to numerous showers and storms, again with hail and strong wind gusts, will redevelop by late morning to midday, as a potent upper level trough and associated very cold temperatures aloft pivot northeastward across the forecast area. While mostly small hail will be common, some may exceed one inch in diameter between 17-23Z. Outlook: At least a couple of clusters of showers and storms, some strong to severe, and with gusty outflow winds surging well away from them, will return to portions of central and/or northern NC for Sat afternoon through Sunday. The approach and stall of a couple of cold fronts east of the Appalachians may result in a band of MVFR ceilings over central NC Mon night, and also a small chance of diurnal convection both Mon and Tue.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...WSS SHORT TERM...Hartfield LONG TERM...MWS AVIATION...MWS

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