Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 251746 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 145 PM EDT Tue Apr 25 2017 .SYNOPSIS...
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Low pressure will move slowly northeastward over eastern North Carolina today, and then push off the Mid Atlantic coast tonight. High pressure will extending from the Atlantic westward into the Southeast states Wednesday through Thursday.
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&& .NEAR TERM /Today and Tonight/...
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As of 945 AM Tuesday... Rainfall rates are improving, but flooding persists in many places this morning. Flood warnings remain in effect for much of north central NC. The mid level low analyzed over SE NC this morning will wobble to the NNE over E NC through today. The band of heavier rain, supported in part by strong upper divergence and steep (~6.5 C/km) 700-500 mb lapse rates atop strong low level mass convergence, will continue to pivot to the west across the NE Piedmont, although rates and intensity have diminished in the last couple of hours with warming cloud tops as the drier air pushing westward over eastern NC, wrapping around the mid level low, steadily erodes the precip shield. The latest HRRR runs and other CAMS support a trend toward lighter rainfall as this band pivots W and WSW into the Sandhills and W Piedmont over the next few hours and decreases in coverage. Additional isolated to scattered convection is expected over NE NC this afternoon beneath another batch of weaker upper divergence, deep 6+ C/km lapse rates, and abundant low level moisture. Have adjusted precip chances through today to account for this scenario. Expect highs of 60-65 over much of the Piedmont and Sandhills, where the stable pool should stay locked in with low level cold air advection and considerable cloudiness, and 65-72 over the Coastal Plain and far southern CWA, which are more likely to see a little sunshine. -GIH Earlier discussion from 745 am: 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/...
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As of 400 AM EDT Tuesday... Lead short wave trough will lift from the Mid MS/TN Valley NE into the Great Lakes on Thulate rsday 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.
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&& .AVIATION /18Z Tuesday through Sunday/...
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As of 135 PM Tuesday... MVFR cigs and patchy showers (yielding brief MVFR vsbys) will dominate central NC terminals this afternoon, followed by gradual SW-to-NE improvement to VFR areawide late tonight. A strong and slow moving upper level low will track toward the NE over eastern NC for the rest of today, before shifting to our NE and off the Delmarva coast tonight. Low level moisture continues to rotate around this low this afternoon, with MVFR cigs over all but RWI, where dry air wrapping around the low has progressed inland from the coast, leading to VFR cigs there, although a period of MVFR cigs remains possible as the moisture over the Piedmont shifts to the NE behind the departing low. Cigs should lift to VFR by 00z at INT/GSO as surface winds become light from the NW, although the moisture circulating around the exiting low will keep a threat of MVFR to IFR cigs at RDU/FAY/RWI into the overnight hours, with RWI potentially not reaching VFR until 10-12z Wed morning. VFR conditions will prevail after 12z Wed areawide as a weak high pressure ridge noses in from the Atlantic. Surface winds will be mostly light and becoming W or NW through tonight. Looking beyond 18z Wed, shallow fog is possible early Thu morning within a light moist flow from the SW, followed by a better chance of MVFR/IFR fog/stratus each late-night through morning, Fri through Sun. A few storms with sub-VFR conditions are possible Sat and Sun afternoon. -GIH
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&& .HYDROLOGY... As of 140 PM Tuesday... The flood watch expired this morning, with no threat for additional heavy rain. However, ongoing high water on area roads and in numerous creeks has prompted an areal flood warning for much of central NC through this evening. In addition, river flood warnings are in effect for several mainstem rivers across the area. See water.weather.gov/ahps2/index.php?wfo=rah for additional information. $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/Vincent SHORT TERM...CBL LONG TERM...CBL AVIATION...Hartfield HYDROLOGY...WFO RAH

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