Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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648 FXUS62 KRAH 211757 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 158 PM EDT SAT MAY 21 2016 .SYNOPSIS...Deepening low lifting up the mid Atlantic coast will drag a surface front and attendant second wave across the area this evening. A strong upper level low pressure area will swing over the region tonight through Monday, bringing continued unsettled weather. && .NEAR TERM /today through tonight/... As of 955 AM Saturday... Rest of today: Primary band of steady widespread showers is currently moving through eastern portions of the Coastal Plain, near a surface low pressure center over NE NC, and is on pace to be out of the CWA shortly, as its primary driving mechanisms -- including mid level DPVA (associated with a vorticity max) and an upper divergence max -- pivot ENE in the base of the incoming longwave trough. A second and much smaller wave noted on water vapor imagery shifting east out of the northern NC mountains is apt to spawn another band of showers that will sweep eastward across the northern CWA over the next several hours. Finally, and most notably, models show yet another vorticity lobe tracking out of the mountains and across NC/VA later this afternoon into this evening, in tandem with lowering surface pressures as the primary low over WV fills with new low pressure forming over the NC Foothills. This upper forcing will likely have available to it at least marginal diurnal instability, provided there is sufficient insolation this afternoon. However, timing of this feature among the hi-res models varies quite a bit, and thus the presence of sufficient instability to support any resultant convection is in question. Both convection-allowing and parameterized models do show good deep layer bulk shear of 40-50 kts this afternoon/evening, and the HRRR shows organized convection over the mountains pushing eastward and into the CWA later this afternoon, a pace similar to most NCAR ensemble members and the hi- res ARW/NMM. Will retain the general flavor of the earlier forecast in bringing scattered showers and storms across the area late afternoon into early evening. The marginal instability will limit storm severity today, however a few storms could still become strong with strong wind gusts primarily across the southern CWA (along and south of highway 64), particularly if the clouds break enough to allow a couple of hours of good heating. Given the current cloud breaks already, have made minor temp adjustments upward to a range of 70 NE to near 80 near the SC border. -GIH Earlier discussion from 400 am: For this evening, widely scattered showers will move back in and across central NC from the NW and as the next short wave assoc with the closed low moves across our area. While the airmass across the NW Piedmont will not have recovered from the CAD and is expected to remain cooler and stable, a sfc boundary trailing the exiting coastal low is progged to extend across portions of central NC generally along and south of Hwy 64. South of this boundary, the airmass may be warm enough to support isolated thunderstorms, some of which could become marginally strong due to 30-40 kt of 0-6km bulk shear coincident with the area of best CAPE south of the boundary. Right now, SWODY1 shows much of our CWA (mainly south of Hwy 64) in a marginal risk for severe tstms later today, with isolated severe tstm wind gusts the main threat. Lows tonight in the mid 50 nw to around 60 S/SE. && .SHORT TERM /Sunday and Sunday night/... As of 400 AM Saturday... The risk for scattered showers and isolated thunderstorms will continue through this period as the closed low over PA drifts south across the Mid-Atlantic region and NE NC. POPs during this time will be highest NE in closer proximity to the upper low center, and lowest SW closer to the subsident region of the pattern and subsequent drier airmass. In fact, there`s a good chance that places west and south of a line from Lexington to Fayetteville may remain dry during this time. Temps will continue to run 5-10 deg below normal. Highs Sunday in the lower to mid 70s and lows Sunday night in the lower to mid 50s. && .LONG TERM /Monday through Friday/... As of 300 AM Saturday... Monday and Monday night: An upper level low over NC will gradually shift eastward then northeastward along the Mid-Atlantic coast through Monday night. A slight chance for showers will linger on the back side of the low as it pulls away. The associated surface low will strengthen as it moves north-northeastward along the coast. Surface winds will be mainly NW, shifting to more westerly as the low departs. As a result, expect highs Monday topping out in the mid 70s and overnight lows in the mid 50s. Tuesday through Friday: The upper level low and attendant trough will quickly move away from the area, replaced by ridging aloft. Similarly at the surface, high pressure will build into the region, though central NC will still be on the back side of the departing surface flow Tuesday, resulting in lingering westerly winds. As the low races off to the NE Tuesday night, surface winds will become more southerly. With the surface high and upper level ridge over the region skies will be mostly sunny/clear mid week with moderating temperatures. Weather will remain dry, likely through Wednesday night, with a slight chance for showers and afternoon thunderstorms returning late in the week. Model agreement still is not great at this time so will keep chances limited to slight. Highs in the upper 70s to mid 80s Tuesday will moderate into the mid to upper 80s by Wednesday, where they will remain through the end of the week. Overnight lows will generally be in the mid 60s. && .AVIATION /18Z Saturday through Thursday/... As of 158 PM Saturday... 24 hour TAF period: Largely in response to strong insolation, lingering CAD over the region continues to weaken. Ceilings have lifted to either MVFR or low-end VFR across the area, with most areas expected to lift to low-end VFR by 21z. As the mid-level trough begins to move over the area, scattered showers and thunderstorms are expected to re-develop across central NC between 21z-06z, resulting in local IFR conditions. More widespread IFR conditions will develop later tonight due to low clouds and some fog, esp invof areas that received heavier rain. The low ceilings/stratus will be slow to lift through the day on Sunday morning, with the potential for MVFR ceilings to persist at eastern/northeastern NC(KRDU and KRWI)until late in the afternoon. Meanwhile...western and southern most terminals could see VFR conditions return by mid morning. Beyond 18z Sunday: the risk for sub-VFR conditions with scattered showers will continue through at least mid-day Monday as a closed low gradually moves south across eastern NC. VFR conditions expected to return by Tuesday and remain for the mid-week period as the closed low moves east and short wave ridging moves over our region. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield/RAH SHORT TERM...RAH LONG TERM...RAH AVIATION...CBL

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