Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 231523 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1123 AM EDT Tue May 23 2017 .SYNOPSIS... A series of low pressure systems will cross central NC through mid- week, causing periods of showers and thunderstorms. Improving weather conditions are anticipated by late in the week. && .NEAR TERM /today through tonight/...
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As of 1123 AM Tuesday... ...Flood watch continues through this evening... Mid-level perturbations, embedded within the deep cyclonic flow around the digging upper low centered over MN/IA and associated long wave trough encompassing much of the central/eastern CONUS, will continue to eject northeastward, atop a quasi-stationary frontal zone bisecting the SE states. With high PWAT of 1.5-1.8"(150 to 200 percent of normal and near daily record values) continuing to pool along this complex frontal zone through tonight, the threat of flooding will persist, with the next batch of moderate to heavy rain expected to move into the area this afternoon as the next prominent upper level disturbance currently over the Deep South/western Florida Pan Handle. With the approach of this disturbance, models predict a wave of low pressure will develop along the front, which will serve to strengthen the low-level moisture convergence, particularly along and just on the cool side of the frontal zone where low-level f-gen will be maximized. Additional storm total amounts of 1-2" are likely with locally higher totals probable. Review of 24 hour rainfall totals over the past 24 hours indicate two areas of heavy rainfall: 1)Across the Sandhills and southern coastal plain where yesterdays convection produced an expansive area of 1 to 2 inches with some localized higher amounts up to 3 to 3.5 inches; 2) More localized/isolated 1 to 2 inches across portions of Forsyth and Guilford counties. In between these two areas, 24 hour rainfall amounts have generally been around 0.50". While the two highlighted areas above will likely be most susceptible to flooding, heavy rainfall of 2 to 3 inches in a short period of time could cause flooding anywhere, thus flood watch will continue for all of central NC. The threat of the heavy rain and flooding looks to be over aoa 06z, once the upper disturbance pushes NE of the area. Hampered by widespread cloud cover and rain, severe threat will be isolated and confined to the southern coastal plain(Sampson/Wayne counties),where weak to moderate buoyancy developing east of the sfc low combined with strengthening effective shear of 40 to 50 kts could support an isolated tornado and straight line damaging winds. Temps have a high error potential today, as any amount of sunshine in the SE CWA could send readings soaring. Will go with highs from the mid/upper 60s NW to the upper 70s/80 SE. Lows tonight 58-65.
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&& .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... As of 410 AM Tuesday... Little change in forecast weather pattern and forecaster rationale since 24 hours ago. Potential severe weather event on Wed looks very similar to the surface evolution/pattern, storm mode, and timing experienced a couple of weeks ago/on May 5th. An initially (slightly) positively-tilted longwave trough from ern Canada to the srn Plains, including an embedded mid-upper low over the mid MS Valley/upper Midwest at 12Z Wed, will migrate ewd and assume an increasingly negative-tilt as it pivots across the Carolinas and middle Atlantic states by Thu and Thu night. Fast, perturbed, and moist SSWly to Sly flow aloft will precede the trough. A complex pattern will result at the surface through the middle of the week. A frontal zone will likely be draped SWwd from a series of waves passing across and offshore the Middle Atlantic coast, marking the srn periphery of weak ridging/CAD/low ovc extending across most of VA/NC at the start of the day Wed, then extending NWwd as a warm front to a low over the wrn OH Valley. That front, edge of the CAD regime, and focus for convection, will then likely retreat Nwd with a narrow wedge of warm sector through srn and perhaps portions of ern NC during the day Wed, then through the remainder of central NC early Wed night, all immediately ahead of, and associated with, a triple point low that will develop and migrate across the wrn Carolinas very late Wed afternoon and Wed night. Initial CAD conditions, and subsequent convection along the retreating warm front, will tend to slow the retreat of the unstable warm sector and nrn bound for any severe threat through much of Wed, such that any strong to severe potential will likely remain from Wadesboro to Goldsboro and Rocky Mount and points SEwd. That unstable warm sector should then surge Nwd through the remainder of central NC early Wed night, immediately ahead of the triple point low, yielding brief --but likely sufficient-- (weak) destabilization to support surface-based QLCS storms capable of producing both swaths of damaging straight line winds and isolated tornadoes along embedded mesovortices/bows/lewps. The cold/occluded front will cause the warm sector and associated severe threat to collapse Ewd and through the Coastal Plain late Wed night-early Thu. Brief drying and clearing will be probable through early midday Thu, but clouds will redevelop with heating, with an additional band or bands of convection --in fast,cyclonic, and CAA-bearing flow aloft-- which will spread NEwd across central NC through late afternoon, the wrn edge of which may result in a strongly forced line of storms along the ern periphery of focused forcing for ascent accompanying the aforementioned upper trough/low. Cold temperatures/steep lapse rates aloft will favor small hail in even marginally strong cores; and a 50-70 kt SSwly speed max on ern fringe of the upper trough will support organized storm modes, including low-topped (splitting) supercells, given long and relatively straight forecast hodographs, which would be capable of producing severe hail and damaging straight line winds. Any tornado threat would be mitigated by both a veering of the low level flow to SWly (Ie. no backing of the sfc flow) and sfc dewpoints aob 60 degrees that would favor evaporatively-cooled downdrafts and cool RFD`s. Temperatures will be slow to climb into/through the 60s on Wed, probably reaching calendar day highs at Piedmont sites between 00Z and midnight, with afternoon highs in the 70s probable over the sern tier or two of counties. Lows in the 60s Wed night, and highs Thu in the upper 60s to 70s, inhibited by both variably to mostly cloudy skies and convection during the afternoon. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... As of 415 AM Tuesday... Dry conditions will return by Thu night, as the upper trough lifts away and weak high pressure expands across the sern states through early Sat. A warm front will develop newd across the central Appalachians later Sat and across the Middle Atlantic states by Sun; with a return to warmer and more humid conditions, and a chance of convection --some probably severe owing to 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 by the weekend-- focused along and north of the front late Sat afternoon onward. && .AVIATION /12Z Tuesday through Saturday/... As of 645 AM Tuesday... Poor aviation conditions will dominate today through tonight. Areas of showers and isolated storms will spread over central NC throughout the day, lasting through the evening, producing mainly MVFR to IFR conditions with low clouds and periods of moderate to heavy rain. Details regarding the specific timing of the heavy rain and storms is uncertain, but we do have confidence in poor aviation conditions dominating through tonight, as low (mainly IFR) cigs are expected to persist overnight even as the heavier rain departs from west to east between 00z and 06z. A surface front oriented SW to NE across central NC will hold in place today as low pressure tracks northeastward along it, leading to erratic winds at central NC terminals, mainly from the SE/S shifting to SW at FAY, and mainly from the NE elsewhere through tonight. Looking beyond 12z early Wed morning, adverse aviation conditions are likely to hold Wed through Wed night as a deep mid level trough and surface cold front approach from the west, bringing another round of heavy showers and a few potentially strong thunderstorms. Improvement to mostly VFR is expected Thu, although scattered afternoon showers generating MVFR conditions are possible. VFR conditions should return for Fri/Sat as a weak high pressure ridge extends into the area. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch through late tonight for NCZ007>011-021>028- 038>043-073>078-083>086-088-089. && $$ SYNOPSIS...Badgett NEAR TERM...CBL SHORT TERM...MWS LONG TERM...MWS AVIATION...Hartfield is the U.S. government's official web portal to all federal, state and local government web resources and services.