Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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495 FXUS62 KRAH 251934 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 334 PM EDT Tue Apr 25 2017 .SYNOPSIS... Low pressure will move slowly northeastward over eastern North Carolina this afternoon, and then push off the Mid Atlantic coast tonight. High pressure will extend from the Atlantic westward into the Southeast states Wednesday through Thursday. && .NEAR TERM /through Tonight/... As of 215 PM Tuesday... Lingering high water on many area roads and in creeks necessitated an areal flood warning through this evening for a large chunk of central NC. However, the heavy rain threat is done, and water should continue to recede on roads and in creeks. Flooding will persist, though, on many mainstem rivers (see hydro section below). The mid level low, stacked nearly atop the surface low, will move to the NE over coastal areas of NC through early evening, before passing off the Delmarva coast tonight. Confluent cyclonic low level flow acting on residual moisture favors a lingering threat of scattered showers on the W/SW side of the low into the evening as it pulls away slowly. A storm or two also remains possible over the far NE CWA, where observed mid level lapse rates are around 6-6.5 C/km, low level lapse rates are nearing 7 C/km, and MUCAPE is 500-1000 J/kg, thanks to some sunshine. Vorticity lobes pivoting around the low may also contribute to ascent. Will hold onto areas of chance pops into early evening. Drier air eventually building in from the WSW in the wake of the low overnight will lead to a clearing trend from SW to NE, with NE sections the last to see the benefits of downslope flow and falling dewpoints. Expect lows tonight in the lower 50s west ranging to around 60 in the far E. -GIH && .SHORT TERM /Wednesday and Wednesday night/... As of 305 PM Tuesday... Mid level ridging will build gradually over the area from the SW through Wed night, with a drying column and 850-700 mb stabilization. Expect little more than scattered flat diurnal cumulus clouds Wed afternoon. Thicknesses and good mixing up through 850 mb support highs of 79-84. Skies should be mostly clear Wed night, although the light SW flow leading to increasing dewpoints topped with strengthening warm advection just off the surface may encourage formation of fog areas late Wed night. Lows 59-63. -GIH && .LONG TERM /THURSDAY THROUGH TUESDAY/...
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As of 330 PM Tuesday... A fairly stout upper trough will lift out of the southern Plains on Thursday, though the core of the upper forcing will pass through the Ohio Valley. Limited moisture transport off the GOMEX and lack of better forcing should result in a decreasing chance of convection as the front attempts to cross the mountains late Thursday. The front it self may nit actually make it across the mountains, so just a few showers are possible as a pre-frontal trough moves into the Piedmont. A sub-tropical ridge will then expand across the Southeast through the weekend as an upper low develops over the southwest US, resulting in thicknesses nearing 1410m and near record heat peaking Saturday. these thicknesses support highs climbing in the upper 80s and lower 90s, about 10-15 degrees above normal. Climatological convective chances will be diurnally driven and focused in the higher terrain, though GFS forecast soundings indicate rather strong instability by Saturday, which is plausible given that the upper ridge is centered to our south and the cap will be weaker to the north. Height aloft then lower Sunday and Monday as the aforementioned upper low lifts toward the Great Lakes, but the influence of the upper ridge may still be felt over the east, leading to highs more in the lower 80d west to upper 80d east. A stronger cold front attendant to the upper low will is forecast to move through Monday, bringing a better chance of showers and storms and temps falling back toward normal by the middle of next week.
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&& .AVIATION /19Z TUESDAY THROUGH SUNDAY/... As of 135 PM Tuesday... MVFR cigs and patchy showers (yielding brief MVFR vsbys) will dominate central NC terminals this afternoon, followed by gradual SW-to-NE improvement to VFR areawide late tonight. A strong and slow moving upper level low will track toward the NE over eastern NC for the rest of today, before shifting to our NE and off the Delmarva coast tonight. Low level moisture continues to rotate around this low this afternoon, with MVFR cigs over all but RWI, where dry air wrapping around the low has progressed inland from the coast, leading to VFR cigs there, although a period of MVFR cigs remains possible as the moisture over the Piedmont shifts to the NE behind the departing low. Cigs should lift to VFR by 00z at INT/GSO as surface winds become light from the NW, although the moisture circulating around the exiting low will keep a threat of MVFR to IFR cigs at RDU/FAY/RWI into the overnight hours, with RWI potentially not reaching VFR until 10-12z Wed morning. VFR conditions will prevail after 12z Wed areawide as a weak high pressure ridge noses in from the Atlantic. Surface winds will be mostly light and becoming W or NW through tonight. Looking beyond 18z Wed, shallow fog is possible early Thu morning within a light moist flow from the SW, followed by a better chance of MVFR/IFR fog/stratus each late-night through morning, Fri through Sun. A few storms with sub-VFR conditions are possible Sat and Sun afternoon. -GIH && .HYDROLOGY...
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As of 300 PM Tuesday... Rainfall across central NC over the past 48 hours ranged from 4 to as much as 8 inches across the Tar, Neuse, and Cape Fear river basins, with the heaviest amounts tending to fall across the upper and middle Neuse basin. Significant widespread flooding has largely receded on smaller creeks and streams, and most roads have been re- opened. However, ongoing high water on some roads and on numerous creeks has prompted the extension of an areal flood warning for much of central NC through early tonight. This rain resulted in major river flooding on the Neuse river at Clayton, while downstream, Smithfield is expected to reach major flood stage this evening. Flooding at forecast points in the Tar river basin will reach moderate flood stage, while only minor flooding is expected at forecast points along the larger Cape Fear basin. See water.weather.gov/ahps2/index.php?wfo=rah for the latest forecasts and for additional information.
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&& .RAH WATCHES/WARNINGS/ADVISORIES...
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None.
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&& $$ SYNOPSIS...SMITH NEAR TERM...HARTFIELD SHORT TERM...CBL LONG TERM...SMITH AVIATION...HARTFIELD HYDROLOGY..Moneypenny

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