Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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835 FXUS62 KRAH 240729 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 330 AM EDT Mon Apr 24 2017 .SYNOPSIS... An upper level low and attendant low pressure system will track southeast from the Deep South to the Southeast coast this afternoon, then lift slowly northeast along the Carolina and Mid-Atlantic coast tonight and Tuesday. && .NEAR TERM /through Monday/... As of 910 PM Sunday... Flood watch remains in effect through early Tuesday morning. Highest threat for prolonged steady light-moderate rain will occur across the western third of central NC through the overnight period. Main adjustment to the near term forecast was to adjust PoPs based on radar trends, and adjusted hourly temps based on cooler observed early this evening. An abnormally deep upper level low over the TN Valley early this evening will drift south-southeast to a position along the AL/GA border sw of ATL by Monday morning. The steady stream of moisture ahead of this system that has been riding over the higher terrain of eastern TN/western NC will also re-aligned its orientation with the low`s movement, and extended from coastal SC into the western Piedmont of NC on Monday. Strengthening sly flow in the 925-850mb layer will tap a moist rich air mass residing over coastal GA/southern SC with precipitable water values of 1.5 inches. The increasing isentropic upglide and increasing divergence aloft will lift this moisture, resulting in widespread showers and associated light-moderate rainfall rates. Potential for heavier rainfall rates to develop very late tonight/early Monday morning as low level convergence increases and convective elements from SC drift into our region. Hourly rainfall rates this evening will vary between a tenth of an inch where light rain is occurring, to a quarter of an inch or a little more where heavier showers occur. Expect the higher rain rates to develop after 06Z in the western Piedmont and linger into early Monday morning. The rain so far has primed the pump, saturating the top soil. The enhanced rainfall rates later tonight should quickly run-off, filling creeks and streams, leading to increased flooding potential of creeks, streams, low lying areas prior to daybreak across the western Piedmont, including the Triad region. Expect additional rainfall amounts of 1-1.5 inches across the western half of central NC overnight, and a half inch or less across the eastern half. On Monday, it now appears the focus for prolonged moderate-heavy rain will shift to our southern counties as the low level flow continues to back in response to the deep low drifting east across GA. Strong low level easterly flow will set-up across our southern counties by Monday afternoon-early evening. Low-mid level confluence coupled with persistent upper divergence will maintain strong lift of the moisture rich air mass, resulting in widespread showers and isolated storms. Expect the northern extent of the widespread moderate-heavy showers to remain just south of the Triad, though reach up toward the Triangle area, with coverage expected to taper off to the north-northeast of Raleigh. Additional rainfall amounts of 1-2 inches highly probable across our southern counties with another half to one inch probable across the north. The approach of a sfc low up the SC coast Monday afternoon, may spread an unstable air mass into our southeast counties, roughly east of a Laurinburg-Goldsboro line. Strong kinematics coupled with a slightly unstable, sfc based air mass may support the development of isolated strong/severe thunderstorms with the main severe weather threats strong/damaging wind gusts or a weak tornado. At this time, the probability of occurrence appears low/weak. High temperatures Monday dependent upon the extend of shower coverage and whether the warmer air residing offshore is able to be advected inland in to our southeast counties. Forecast high temps should vary from the mid-upper 50s nw half to 65-70 far southeast. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
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As of 330 AM Monday... The vertically stacked/mature low pressure system will track slowly north across eastern NC Tuesday and Tuesday night and then off the Delmarva coast on Wednesday. With the mid-level dry slot encompassing the area Tuesday morning, there could be a lull/minimum in precip/pops across central NC to start the day. However, diurnal heating and resultant weak destabilization(at least across the eastern and possibly central zones) as the wrap-around moisture band pivots NE through the area, is expected to lead to convective re-development Tuesday afternoon and evening. The threat for severe storms will be muted by the lack of greater instability but given the presence of an occluded front draped somewhere across eastern/east-central NC, cannot rule out an isolated severe threat. Additionally, with the potential for slow- moving/training convection with the wrap-around band, isolated flooding, especially in low-lying or poor drainage areas will be possible. Highs Tuesday afternoon will be challenging, complicated by multiple boundaries draped across the area. Expect one sharp temperature gradient invof of where the aforementioned occluded front sets up across eastern NC, with another tight temp gradient along the lingering CAD airmass across the western Piedmont. Highs ranging from upper 50s NW to mid/upper 70s east. Rain chances will slowly taper off from SW to NE Tuesday night, finally coming to an end across the NE zones early Wednesday morning as the mature cyclone lifts away from the area. Lows Tuesday night in the mid to upper 50s Tuesday night.
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As of 330 AM EDT Monday... In the wake of the low lifting up the Mid-Atlantic coast, low-level swly flow and short wave ridging aloft will mark the return of sunshine and warming temperatures. Highs in the upper 70s to lower 80s Wednesday, warming into the lower and mid 80s by Thursday. On the southern periphery of dampening short wave energy lifting through the MS and Ohio Valleys NE into the Great Lakes, we could see isolated/slight chance of showers and storms Thursday night and Friday. Otherwise, it will remain mostly dry with the main weather headlines being the hot temperatures associated with the dominate subtropical ridge building across the SE US. Highs Saturday and Sunday in the upper 80s to lower 90s.
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&& .AVIATION /06Z Monday through Friday/... As of 230 AM Monday... 24-hr TAF Period: Adverse aviation conditions in the form of IFR/LIFR ceilings and rain are expected through the TAF period as a potent upper level low and attendant surface low track southeast from the Deep South to the Southeast coast. Elevated showers and thunderstorms /heavy rainfall/ will be possible at all terminals late this morning through this afternoon. Northeast winds initially at 5-10 kt will increase to 10-15 knots with gusts to 20-23 knots after sunrise. The FAY terminal could see light/variable or southeast winds along with improved ceilings (MVFR or possibly VFR) for several hours this afternoon, depending on the precise track of the aforementioned surface low as it progresses toward the Southeast coast. Looking Ahead: Adverse conditions are likely to persist in association with a lingering CAD wedge over the area Tue/Tue night. Ceilings are gradually expected to lift/scatter out to VFR during the day Wednesday as the upper level low lifts northeast along the Mid-Atlantic coast. -Vincent && .HYDROLOGY... As of 910 PM Sunday... ...A Flood Watch is in effect through 800 AM Tuesday... The threat for flooding of creeks and small streams is expected to increase late tonight into early Monday across the western Piedmont including the Triad region as the ground saturates and the rainfall becomes heavier. The threat for flooding along creeks and streams expected to encompass the remainder of central NC Monday into Monday night. Minor river flooding will become more likely later Monday and could linger into midweek. Based on our expected rainfall distribution at this time, the Haw river would be particularly prone to minor flooding above Lake Jordan, but any of the mainstem rivers could reach minor flood stage, especially given just a bit more rain than currently forecast. On a positive note, we were on the cusp of drought conditions due to rainfall deficits over the late winter and spring, so this event will turn that around and possibly eliminate much of a drought threat for the rest of the spring season. && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043- 073>078-083>086-088-089. && $$ SYNOPSIS...Vincent NEAR TERM...WSS SHORT TERM...CBL LONG TERM...CBL AVIATION...Vincent HYDROLOGY...WSS/MLM is the U.S. government's official web portal to all federal, state and local government web resources and services.