Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 241756 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 155 PM EDT Mon Apr 24 2017 .SYNOPSIS... A strong and deep low pressure system will slowly cross the region through Tuesday, producing wet and unsettled weather. Behind this low, a ridge of high pressure will extend into the region for mid to late week. && .NEAR TERM /Today and Tonight/... As of 910 AM Monday... Forecast of steady moderate to heavy rain covering central NC remains valid. Deep mid-upper low pressure wobbling into west central GA with a negative tilt will continue to draw deep moisture into the Carolinas, with PW values expected to near 1.5", which would place values near record highs, according to PW climatology. Low level moisture transport and convergence are expected to remain focused over our area, from Laurinburg, Lumberton and Fayetteville up through SW portions of the Triangle region in particular, and this is where the primary bands of significant rainfall should line up. The surge of moisture and precip intensity should increase through the day as 850 mb onshore-directed flow strengthens to 35 to 45 kts, pumping greater amounts of Atlantic moisture into the area, north of a shortwave riding from the Bahamas northward off the SE coast through the day. Have raised storm total rainfall to near 5 inches in the SE (Laurinburg/Raeford/Fayetteville) to 3-4 inches in the Triad, 2-3 inches in the Triangle, and near 2 inches in the far NE. Street flooding remains likely, along with rapid creek rises especially in the Triangle to the south and west. No changes to the flood watch at this time. It will remain chilly today with widespread rain and thick clouds, with highs from the lower 50s NW to the mid-upper 60s in the far eastern Coastal Plain. -GIH Earlier discussion from 345 AM... Overview: An upper level low centered over northern AL at 06Z will track SE/ESE to the Southeast coast this afternoon and evening. An attendant surface low will track eastward to the GA/SC coast this evening, then lift slowly northeast along the North Carolina coast late tonight. Precipitation: With the upper level low /attendant surface low/ expected to track E/SE across GA/SC and an established CAD wedge in place over central NC, the narrow warm sector in southern GA/SC is expected to shift N/E through eastern SC to coastal NC this aft/eve. As such, convection should remain elevated in nature over central NC. A N-S oriented band of elevated convection over western NC will shift eastward into central NC today and assume a NW-SE orientation this afternoon as the upper level low progresses SE from northern AL to eastern GA and low-level flow strengthens/backs to the Southeast off the Atlantic. In close vicinity to the warm front (southern Cumberland and Sampson counties), a narrow window for sfc-based convection (and an attendant severe weather potential) cannot be ruled out this afternoon. Otherwise, any threat for severe weather should remain along/east of Hwy 17 near the Carolina coast. The primary band of elevated convection will assume a W-E orientation tonight as the upper low passes to the south and low-level flow over central/eastern NC backs to an easterly direction. The heaviest rain will fall where the band of elevated convection pivots as it transitions from a N-S orientation to a W-E orientation this afternoon into tonight. Temperatures: With regard to temperatures, a pronounced CAD wedge is expected to remain in place across the N/NW Piedmont through tonight, with little variation in temperature (upper 40s to lower 50s). From the Triangle south and east, the modified CAD wedge should vary little through the day (except perhaps in the far SE Coastal Plain for a few hours this afternoon), though temperatures will likely rise from east to west overnight as surface winds strengthen from the east and advect a higher theta-e airmass inland from the coast. -Vincent && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... 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. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... 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. && .AVIATION /18Z Monday through Saturday/...
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As of 155 PM Monday... High confidence in poor aviation conditions through at least 06z tonight. Thick IFR and occasionally LIFR based clouds will persist over central NC as a deep and strong low pressure system slowly crosses the area through Tue, exiting to our northeast Tue night. Periods of rain through 06z will affect all sites with occasional MVFR to IFR vsbys, along with the mainly IFR cigs. Cigs will slowly lift Tue morning to MVFR with decreasing vertical extent as drier air just off the ground arrives from the S. The rain will decrease in coverage and intensity later tonight, although scattered showers will persist after sunrise Tue as the core of the upper low passes overhead. Surface winds will be mainly from the NE at 7-12 kts through tonight, occasionally gusting to 15-20 kts during the evening and overnight hours, especially at GSO/RDU/RWI as an easterly low level jet at 1000-2000 ft AGL extends into the area. This low level jet may lead to a risk of low level wind shear at INT/GSO/RDU/RWI from late evening into the overnight hours. Surface winds will then decrease late tonight (after 09z) and become more from the N or NW Tue. Looking beyond 18z Tue, cigs should remain MVFR through Tue night, with infrequent MVFR vsbys in scattered showers, although cigs may drop back to IFR through Tue night especially at INT/GSO as a cool stable air mass persists there. After the low shift to our NE Tue night, high pressure ridging will take over, and we`ll see cigs rise to MVFR then VFR through Wed morning. VFR conditions will then dominate through Sat. -GIH
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&& .HYDROLOGY... As of 330 AM Monday... ...Flood Watch remains in effect through 12Z Tuesday... Widespread heavy rain is expected to develop over central NC today into tonight. Storm total rainfall amounts of 3-5" are expected, with locally heavier amounts possible where the primary band of elevated convection pivots /persists the longest/. Flooding of local creeks and streams can be expected. Main stem rivers will experience significant rises in water levels this afternoon into tonight, particularly the Yadkin, Haw, Neuse, Tar, Roanoke, and Cape Fear. && .RAH WATCHES/WARNINGS/ADVISORIES... Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043- 073>078-083>086-088-089. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...Hartfield HYDROLOGY...Vincent/RAH

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