Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 240639 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 238 AM EDT Mon Apr 24 2017 .SYNOPSIS...
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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.
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&& .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 /Monday night through Tuesday/... As of 330 PM Sunday... The threat of flooding will continue with heavy rain gradually tapering off from the west Monday night into Tuesday morning. The severe threat should end as the low pressure and cold front shift offshore early Tuesday. Rain will continue over much of the eastern half of the region through at least mid day as the low tracks up the coast. Cloudiness and northerly low level flow will keep many areas in the upper 50s and 60s Tuesday, with the warmest readings in the SW, where some clearing may take place. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... As of 330 PM EDT Sunday... A short wave ridge will quickly move across our region Tue Night through Thu night, resulting in dry warming weather during this time. Highs Wed and Thu in the 80s and lows in the upper 50s to lower 60s. A weak short wave in the sw flow is progged to move across the area early Fri. Will include a slight chance pop for daytime Fri. Otherwise, the ridge over the se is progged to amplify over the weekend, keeping the precip-makers to our north and west, and an above normal airmass over our area. Highs in the upper 80s and lows in the mid 60s during this time. && .AVIATION /06Z Monday through Friday/...
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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
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&& .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...Badgett LONG TERM...np AVIATION...Vincent HYDROLOGY...WSS/MLM

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