Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251158 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 758 AM EDT Tue Apr 25 2017 .SYNOPSIS... An upper level low and attendant surface low pressure system will track northeast along the North Carolina coast today, then progress offshore the Mid-Atlantic coast tonight. && .NEAR TERM /Today and Tonight/...
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As of 745 AM Tuesday... ..Flash Flood Watch will be allowed to expire at 8 am EDT... Heavy rain will persist for several more hours in the Triangle, northern Piedmont and NE Coastal Plain before winding down ~15Z as the primary band of elevated convection pivots SW-NE over the western Piedmont and weakens as the Atlantic moisture feed is cutoff over central NC (on the western periphery of the upper level low tracking NE along the Carolina coast). The watch will be allowed to expire given that heavy rain will persist for just a few additional hours and flooding is ongoing at this point /numerous flash flood warnings are in effect/. -Vincent 400 AM Discussion: The NW-SE oriented band of elevated convection streaming inland from the Atlantic early this morning has been associated with strong low-level warm advection (~50 knot easterly H85 flow) and DPVA assoc/w small amplitude waves rotating around an upper level low centered in vicinity of the SC coast at 07Z. Now that the upper level low is tracking east of -79 degrees longitude (roughly), the aforementioned band of elevated convection has pivoted toward a WNW-ESE orientation and will pivot W-E by ~12Z and SW-NE over the N/W Piedmont by ~15Z. Expect the heaviest rainfall /precip rates/ to shift along and north of Hwy 64 from Rocky Mount to the Triangle over the next few hours before weakening after ~12Z. The upper level low tracking eastward this morning will assume a NE motion along the NC coast this afternoon/evening. As shortwave energy /DPVA/ rotates cyclonically from the northern periphery to the western periphery of the upper low centered along the NC coast this afternoon, convection is expected to re-develop over portions of the area. Confidence in coverage is lower than average, however, the bulk of activity should be confined from the Triangle into the northern Piedmont and NE Coastal Plain. Marginal destabilization, low equilibrium levels, and close proximity to the upper low suggest little potential for convective organization this afternoon. Given weak steering flow near the upper low, an isolated flash flood threat could accompany convection that develops in the NE Coastal Plain this afternoon, assuming it persists for a few hours. -Vincent
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&& .SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/... As of 400 AM Tuesday... In the wake of the low pressure lifting up the Mid-Atlantic coast, low-level southerly winds and short wave ridging aloft will mark the return of sunshine and warming temperatures. Highs ranging from upper 70s NE to lower 80s south. Lows Wednesday night in the upper 50s to lower 60s. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 400 AM EDT Tuesday... Lead short wave trough will lift from the Mid MS/TN Valley NE into the Great Lakes on Thursday with trailing sfc cold front expected to stall out west/northwest of the mtns. Associated convection is expected to be ongoing Thursday morning across Tn, Al, and Ga Thursday morning. However with the better trough dynamics/forcing lifting off well to the north Thursday afternoon and evening, the showers and storms should exhibit a steady decline/weakening trend as they cross the mtns Thursday afternoon/evening. Will leave isolated chances across the far western zones Thursday afternoon, otherwise it should remain dry with temperatures steadily rising in the SWLY WAA regime. Highs in the lower to mid 80s west to upper 80s central and eastern areas. The synoptic pattern will favor near record heat by Saturday, owing to a 590+dm H5 ridge, Bermuda highs and H7 anticyclone over SC. Thickness are progged at 1410m Saturday, 50m above normal and indicative of upper 80s to lower 90s. The main question is how quickly another shortwave ejecting out of the Central/Southern Plains, this one potentially stronger, will cause the ridge to retreat offshore a bit. Heights are forecast to lower slightly on Sunday, more so across western NC. Highs in the mid 80s west to near 90 central and eastern area. A cold front will bring the next chance for rain/storms to the area on Monday with cooler temps following on Tuesday. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/...
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As of 745 AM Tuesday... 24 Hour TAF Period: Adverse aviation conditions are expected to continue through the 24 hour TAF period (high confidence) as a deep mid/upper level low moves across the region. Expect IFR/LIFR conditions to prevail at most terminals through this evening, though periods of MVFR/VFR conditions will be possible. The primary band of elevated convection /heavy rain/ will affect the RDU/RWI terminals through late morning. After a lull, scattered convection may re-develop at the same terminals later this afternoon. Ceilings are expected to improve by or shortly after midnight at the GSO/INT terminals, though IFR/LIFR ceilings may persist through the TAF period at eastern terminals. Outlook: After the low shifts NE along the Mid-Atlantic late tonight, VFR conditions are expected to prevail by mid-day Wednesday. VFR conditions will prevail through Sat. -Vincent
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&& .HYDROLOGY... As of 400 AM Tuesday... The flood watch will be allowed to expire at 800 am EDT as precipitation rates decrease and the primary band of elevated convection weakens/pivots to a W-E orientation north of Hwy 64 followed by a SW-NE orientation over the W/NW Piedmont by 12-15Z. If convection redevelops in the NE Coastal Plain this afternoon, an isolated flash flood potential could briefly exist given weak steering flow and slow/nearly stationary motion. -Vincent $$ SYNOPSIS...Vincent NEAR TERM...Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...BSD/Hartfield HYDROLOGY...Vincent

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