Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 191931 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 330 PM EDT Sat May 19 2018 .SYNOPSIS... A moist and slightly unstable air mass will remain entrenched across central NC through the middle of the week. && .NEAR TERM /THROUGH TONIGHT/...
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As of 330 PM Saturday... Main adjustment to the near term was to trim the interior portion of the Flash Flood Watch as the threat for flooding has abated since the main moisture axis and best lift has shifted east into the Coastal Plain. Decided to maintain the watch in the Triad due to the scattered convection approaching from the west. Some convective allowing models along with the HRRR suggest heavy showers in the Triad vicinity around sunset. A Bermuda high offshore will continue to funnel tropical moisture re northward into eastern NC through tonight. This plume of moisture which has been aligned south-to-north the past couple of days, will tilt to a more sw-ne orientation tonight as a mid-upper level trough lifts newd across the Great Lakes. The passage of this feature will veer our mid level winds to a more swly direction, primarily across the northern sections, causing the tilt in the moisture plume. While the bulk of the convection will diminish with loss of heating, the passage of the mid level trough well to our north may sustain scattered convection in vicinity of the Triad into the overnight. Additionally, a few showers probable on the periphery of our eastern and se sections due to proximity of the moisture plume and weak perturbations embedded in the plume.
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&& .SHORT TERM /SUNDAY/...
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As of 330 PM Saturday... Sunday, in the wake of the mid level trough to our north, the mean flow will be westerly. This will lead to a modest drying out of the atmosphere, with precipitable water values across the Piedmont near or slightly below 1.4 inches. Meanwhile the atmosphere will remain very moist across the se third of our forecast area, thanks to the continued presence of the moisture plume. A weak 850-700mb trough is projected to cross central NC Sunday afternoon. This feature will aid to focus low level convergence, leading to the development of scattered thunderstorms, primarily between 3 PM and 9 PM. Wind field aloft not supportive of organized/strong convection at this time, though torrential downpours will cause a renewed threat for localized flooding. It should be warmer Sunday afternoon with most places reaching the low-mod 80s.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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As of 220 PM Saturday... Maritime Tropical airmass will remain over central North Carolina through Wednesday with dewpoints in the upper 60s to lower 70s. Diurnal heating and embedded disturbances in deep southerly flow will contribute to scattered convection each afternoon and evening with a lull in activity overnight and early morning. Any convection will have potential to produce very high rainfall rates given the near record level PWs. High pressure building across the Northeast Thursday may push a backdoor cold front into the area Thursday and Friday bringing a drier airmass and lower chances for convection. On Saturday, southerly flow returns bringing tropical airmass northward into central North Carolina and greater chance for convection.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/... As of 145 PM Saturday... Numerous showers and a few thunderstorms will continue to traverse northward across central NC through early this evening. The showers will be most concentrated over the Coastal Plain, generally along and east of I-95. Widespread MVFR conditions due to ceilings and visibilities in showers will be common in this region. Across the Piedmont, variable ceilings ranging from MVFR in vicinity of KRDU to low end VFR in the Triad will occur. Convection will be isolated to scattered, primarily in proximity to RDU. Showers with heavy rain may threaten the Triad terminals by early evening. Aviation parameters may briefly improve late this afternoon-early evening with ceilings generally low end VFR. Ceilings are expected to lower back to the low end MVFR/IFR range after 06Z, and remain low through late morning Sunday. IFR/MVFR ceilings will occur until early Sunday afternoon. Afterwhich, ceilings will lift to the low end VFR. As the moist and unstable atmosphere heats up, scattered convection will occur. Expect MVFR parameters in proximity of the convection. The weather pattern will change little through Thursday across central NC as the warm moist air mass remains in place. This will lead to a good chance of late night/early morning MVFR/IFR ceilings, followed by scattered afternoon and early evening convection. && .RAH WATCHES/WARNINGS/ADVISORIES...
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Flash Flood Watch until midnight EDT tonight for NCZ007>011-021>023- 026>028-042-043-078-089.
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&& $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...WSS LONG TERM...Franklin AVIATION...WSS

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