Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 212354 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 740 PM EDT Sun May 21 2017 .SYNOPSIS... A warm front will lift north into central NC as a weak low pressure tracks NE across the state tonight. A cold front will stall over central NC Monday. Another system is expected to move NE along this boundary enhancing rain again Monday night into Tuesday. && .NEAR TERM /THROUGH TONIGHT/... As of 740 PM Sunday... Updated the forecast to speed up the timing of the showers/scattered thunderstorms across much of the region overnight. A mesoscale low was tracking NE toward Charlotte as of mid-evening. A warm front extended from the low across southern NC, just south of Fayetteville and north of Wilmington. This front is forecast to move north in advance of the low pressure track NE across central NC this evening. The front may make it to the Triangle before the meso-low and the associated cold front pass the region likely between 200 and 400 am in the morning. In addition, there has been some rotation noted with the scattered thunderstorms that developed just on the cool side of the warm front (near Southern Pines, Raeford, and west of Fayetteville early evening). However, since the convection has been concentrated north of the boundary, the threat of severe storms appears given the stability noted (due to the Cold Air Damming) in place from the Triad to the Triangle to near FAY) on the cool side of the warm front. This cool and stable air is courtesy of the slowly departing surface high that was 1028+ mb off the New England coast - extending down into the Piedmont of NC/upstate SC. As the meso-low tracks toward the Triangle area, the warm front will lift north, and according to most of the hi-res convection allowing models - bring a round of showers/storms northward from the current position into the Triad and Triangle areas. However, the severe threat should remain minimal given the extent of the CAD stability and minimal convective development expected in the small area that would be favorable for severe storms over the far SE Coastal Plain and Sandhills. Rainfall on the order of 0.5 to 1 inch is likely just to the NW of the track of the meso-low, putting the Triad and NW part of the Triangle in the heavier rain. Once the rain tapers off later tonight with the passage of the low pressure, expect low clouds/fog to linger over all but the SE where some clearing can be expected. Lows in general should hold in the lower 60s NW and fall into the mid to upper 60s SE. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 315 PM Sunday... Unsettled weather pattern persist for Monday and Monday night. Lead mid-upper level vort max will continue to lift slowly northeast across southern VA Monday morning. This feature will provide enough forcing to cause a band of showers/isolated thunder to cross the northeast Piedmont/Sandhills and northern coastal plain during the morning hours. This feature should depart our region by mid day. Subsidence in its wake will likely suppress atmosphere enough to limit afternoon convection. Expect just isolated convection Monday afternoon-Monday evening. Next mid-upper level s/w will begin to influence the weather over our Piedmont counties Monday night with an increasing threat for showers and thunderstorms. The next s/w will move along a lingering surface trough stretched southwest-northeast over the western Piedmont. The increasing low level confluence along this boundary coupled with deep southwest flow will enhance the potential for training showers/storms along this feature, especially late Monday night into early Tuesday. Will maintain likely PoPs for now across the western Piedmont but if model trends continue, categorical PoPs will be necessary. A smaller than normal diurnal temperature trend will occur due to extensive cloud cover and morning showers in the east. Highs Monday upper 70s-lower 80s. Low temps Monday night generally mid-upper 60s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 235 PM EDT SUNDAY... Model consensus is a little better depicting a vigorous wave lifting out of the north central Gulf and riding deep southwest flow northeast into NC on Tuesday. Timing issues abound, however, as the GFS would like to lift the wave out a little further north and considerably (~9 hours) faster, which maintains a heavier rain axis west of the area, but cuts off the heavier rain abruptly Tuesday afternoon. Per its more consistency over the past couple of days, will maintain our ongoing ECMWF bias in the timing and QPF amounts, with categorical PoPs into Tuesday night and total rainfall amounts Tue-Thu in the 2.25-3 inch range. The bulk of the heavy rain (up to 2 inches) will fall Tuesday and Tuesday night and there will be a threat of flooding, particularly in our more urban areas, as the southwest flow and slow eastward translation of the system will encourage training convection. Strong low level convergence and low level jet of 40-50 Kts will be sufficient to produce strong storms, but severe potential will be diminished due to limited instability with the widespread antecedent cloudiness and weak mid level lapse rates...your basic high shear/low CAPE environment. Highs will range from ~70 northwest to mid and upper 70s in the coastal plain. Convection...particularly stronger convection...will diminish with loss of diurnal influence as the surface wave lifts north of the area early Tuesday night. However, southwest flow maintains relatively deep moisture transport overnight and through the day on Wednesday as a second cold front approaches from the west. As such, will maintain likely PoPs into Wednesday night, and we could see some pretty vigorous storms develop ahead of this second front on Wednesday afternoon as we will get some modest mid level cooling and drying behind the initial wave to steepen mid lapse rates. Will raise PoPs to the 60% range through the day, diminishing to a chance of showers Wednesday night into Thursday as we get dry-slotted by wrap- around from the cutoff low over the northern Ohio Valley. Highs Wednesday and Thursday will range from 75 to 80. Dryness returns at last on Friday and should persist through the weekend. Initial northwest flow flattens through the weekend, and the cool airmass moderates from the 70s Friday to the low to mid 80s Saturday and Sunday. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... As of 155 PM Sunday... There is a high likelihood of adverse aviation conditions across central NC through Tuesday as a series of upper level disturbances crosses the moist air mass in place across central NC. Each disturbance will kick-off scattered showers and thunderstorms with associated MVFR/IFR ceilings and visibilities. The first disturbance will cross central NC this evening through Monday morning. Another is expected to affect our region late Monday night into Tuesday. In between the periods of showers and storms, MVFR/low end VFR ceilings will prevail due to the available moisture in the atmosphere. The unsettled weather will persist through Wednesday. An improving weather pattern is anticipated by Thursday with VFR conditions highly probable for Thu-Fri. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...WSS LONG TERM..mlm AVIATION...WSS is the U.S. government's official web portal to all federal, state and local government web resources and services.