Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250806 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 405 AM EDT Tue Apr 25 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 /Through Tonight/... As of 1000 PM Monday... Most of North Carolina resides in the left exit region of a jet streak rounding the base of a compact negatively-tilted trough across the southeastern CONUS. The center of a compact surface low pressure can be found across far eastern South Carolina and is moving northeastward with time. A secondary (and stronger) subtropical low is approaching the coast of North Carolina, and is starting to merge with the aforementioned low pressure system to its west. Closer to home, the region remains in a strong CAD regime with the wedge front delineating slightly more warm and moist air and the CAD to its west located across the eastern CWA. As the lows merge, continued DCVA (as well as frontogenetical forcing, and isentropic upglide along a wedge front draped across the southeastern CWA) will continue to enable widespread ascent. Coupled with an anomalously moist atmosphere across the CWA that increases toward the east (the 00z KMHX sounding reflects a PWAT of 1.83", breaking the previous daily record by nearly nearly 0.3"), widespread rainfall continues areawide. Currently, the heaviest rainfall is confined to two main bands--one across Edgecombe to Franklin counties and another across Wayne and Johnston counties. Both bands seem to combine across Wake, Chatham counties. While rainfall rates aren`t particularly intense within the bands (generally a few tenths per hour approaching 0.5"/hr in the heaviest segments), the long duration of the rainfall is leading to 6 hourly rainfall rates of 1-2". Unsurprisingly, recent storm reports indicate a few closed roads across the CWA with rivers rising in the heaviest bands toward flood stage. However, some slight drying is being noted across the far NE CWA into the NE coast of North Carolina (likely in association with vertical mixing of a pocket of drier air centered around 925 mb) leading to an erosion of the northern precipitation band. As the combined low pressure system translates northeastward across the coast of North Carolina, the bands of heaviest precipitation will likely pivot slightly northeastward with time. A quick peak at the latest suite of model guidance indicates a narrow axis of MUCAPE may build into the eastern CWA enabling slightly heavier precipitation rates as the band moves northeastward (especially between 03-06z). Indeed, a few flashes of lightning are occurring across the NC coast within the aforementioned precipitation band. As the band shifts northwestward, an additional 1-2" with isolated pockets of 3-4" seems likely across the NE CWA (e.g. Edgecombe, Nash, Franklin counties) as well as parts of Wake, Durham, Chatham, and Orange counties. The latest mesoscale discussion from the WPC lines up well with this reasoning. && .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 /06Z TUESDAY THROUGH SATURDAY/... As of 155 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. A persistent rain continues to fall across portions of central NC early this morning, resulting in generally IFR/low end MVFR conditions. However, periods of LIFR cigs will be possible in areas of light rain and/or brief lulls in the precip ahead of the mid/upper low (such as KFAY currently). Sporadic wind gusts of up to 22 kts or so will continue to be possible across the northern TAF sites early this morning, before diminishing from east to west through 12Z. Will continue to keep LLWS in the TAFs at KGSO/KINT/KRDU/RWI as easterly winds at around 2 kft are expected to be around 45-50 kts or so through 09Z. However, given this will mostly be speed shear (with generally unidirectional flow) expect this will only create marginal LLWS conditions (especially given some of the gustiness expected). Surface winds will then decrease after daybreak. While the main area of rain will shift northward of the area by 12-15Z today we can still expect some lingering showers/rain, especially moisture wrapping around the departing low pressure system across the northeastern portions of our area (KRWI/KRDU). In fact we could see a few storm develop if we are able to destabilize enough this afternoon. While cigs should improve today, possibly becoming VFR temporarily, think we should generally maintain MVFR cigs. Outlook: Cigs should remain MVFR through tonight, although cigs may drop back to IFR through this evening into the overnight. After the low shift to our NE tonight, high pressure ridging will take over, and we`ll see cigs rise to VFR Wed morning. VFR conditions will then dominate through Sat. && .HYDROLOGY... As of 420 PM Monday... ...Flood Watch remains in effect through 12Z Tuesday... Much of the rainfall so far has been moderate, with most places so far spared by the heavier rain rates. This is expected to change through the evening hours as increasing lift and moisture lead to an uptick in rain rates. Several creeks around central NC are experiencing rises, with a few approaching minor flooding, and this should persist through tonight, with retreating water levels Tuesday. Urban and street flooding, particularly in the typical flood-prone areas, have been common all across central NC. A few main stem rivers are projected to approach or exceed flood stage over the next couple of days in response to this rainfall, including parts of the Yadkin, Haw, Little, Cape Fear, Rocky, and Tar Rivers. Rainfall since last night has been around 1 to 3 inches, and an additional 1-3 inches of rainfall are expected through tonight, with locally higher totals possible. -GIH && .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...BB/MWS SHORT TERM...CBL LONG TERM...CBL/Smith AVIATION...BSD/Hartfield HYDROLOGY...Hartfield

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