Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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552 FXUS62 KRAH 270557 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 156 AM EDT MON SEP 26 2016 .SYNOPSIS...
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A cold front will stall across the Carolinas today through late in the work week, bringing unsettled weather through the period.
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&& .NEAR TERM /OVERNIGHT/... As of 910 PM Monday Have adjusted PoPs upward over the western-nw Piedmont as a band of convection has arrived and has begun to slow its eastward progression. This is raising concerns for a localized excessive rainfall, mainly just south of Winston-Salem and Greensboro, encompassing Lexington and Asheboro, and west of RDU, affecting the Chapel Hill/Carrboro area. Some locations in the area described above may receive 2-3 inches of rain in less than 3 hours before 2 Am Tuesday. This may cause a few creeks and streams to leave their banks and may lead to an isolated road closure or two. Believe the threat is too isolated for a flash flood watch but will continue to monitor. The scenario is a classic set-up with a slowing band of convection becoming perpendicular to a sly feed of moist air. Tonight, this west-sw/e-ne band is encountering a sly south of 15-20kts in the 925- 850mb layer, advecting moist air with precip water values 1.6-1.8 inches, close to 150 percent of normal. Additional lift being supplied aloft by 100kt jet crossing the eastern Great Lakes, placing the nw Piedmont in the favored right entrance region. Farther east, mainly for areas east of highway 1, overcast skies and and a few spotty showers are expected though overall coverage and intensity are expected to be spotty and light. Overnight temps will be fairly uniform due to the overcast skies and light sly flow. Min temps mid-upper 60s. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... As of 250 PM Monday... The cold front will inch eastward into the Piedmont on Tuesday, slowed further by system parallel flow induced by the upper low that will close off and dig toward the Tenn Valley. PW will remain relatively high at 1.75", though the source of higher PW off the coast looks to be cut off by a surface wave that lights northeast along the NC coast. Forcing is pretty much limited to moisture convergence along the front, with better height falls later Tuesday night ahead of the aforementioned upper low. Despite weak lapse rates aloft, highs in the upper 70s/lower 80s should result in weak instability and trigger scattered to numerous showers and a few isolated, mainly in the Piedmont. Increasing mid-level wind fields will increase the shear over the region Tuesday afternoon, but weak instability (better Wednesday) will ultimately limit the threat of severe storms. Based largely on WPC guidance, 0.5-1.0" of rain is generally expected. As mentioned above, forcing aloft is a little better late Tuesday, albeit with less instability (though forecast soundings do show some thin MUCAPE that may enhance parcel lift). The front isn`t expected to make much progress eastward, so there may be a limited flooding threat worth watching Tuesday evening, largely dependent on how active the front is tonight and Tuesday. Lows again in the upper 60s. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... As of 345 AM Monday... PoPs will be higher...chance category...in the east on Wednesday due to proximity of the lingering frontal zone where moisture advection will maintain precipitable waters in excess of 1.5 inches. Dry air wrapping into the area around the upper low will be sufficient to produce a chance of thunder...especially I95 eastward. Highs will be similar to Tuesday...mid-upper 70s with some lower 80s in the southeast. Upper cutoff low over the Great Lakes throws a lot of uncertainty into the forecast heading into the late week...but at this point both GFS and ECWMF stall the southerly and easterly progress of the system in the Tennessee Valley and lift it back north into the Great Lakes over the weekend. Dry trajectory and maintenance of neutral temperature advection around the low supports our ongoing dry and seasonable forecast with highs mostly in the mid to upper 80s. Morning lows will feel nippy...with mins falling into the mid to upper 50s. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/...
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As of 156 AM Tuesday... A pre-frontal band of showers and thunderstorms over the NC Piedmont will move slowly eastward this morning and into the midday hours, diminishing/weakening along the way. IFR to MVFR ceilings through 12z should remain confined to KINT, KGSO, and KRDU, along the axis of stronger low-level moisture transport. These sub-VFR ceilings should gradually lift to VFR between 15 to 18z, with additional showers and storms re-developing across western NC and moving eastward this afternoon and evening as the sfc cold front stalls across western NC. Otherwise, at KFAY and KRWI, expect predominately VFR ceilings with some isolated shower or two possible. Looking beyond the 24 TAF Period: The combination of a quasi- stationary front across the Carolinas and a cut-off upper level low settling over the Tennessee Valley will keep unsettled weather in the form of scattered to numerous showers and storms through Thursday. Drier air from the west should gradually advect east into the area late Thursday and into Friday, leading to improving conditions with dry VFR conditions expected Friday and Saturday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...BS LONG TERM...MLM AVIATION...30/BS

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