Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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440 FXUS62 KRAH 261758 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 150 PM EDT MON SEP 26 2016 .SYNOPSIS... A quasi-stationary front across southwestern NC will return north as a warm front today as a cold front approaches from the west. The cold front will move very slowly southeast through the area Tuesday and into Wednesday. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM Monday High pressure off the New England coast extends into east-central NC this morning, with an east-southeasterly flow banking moisture up against the mountains and ceilings varying from below 1000ft in the west to 3000-4000 ft in the east. Persistent convection around the Charlotte Metro area has shown signs of waning in the past couple of hours, likely owing to a relaxation of the nocturnal LLJ and weaker isentropic accent. This precip, along with addition showers expected to trigger within an instability axis running up the foothills this afternoon, will have less moisture and forcing to work with as the mid-level flow carries it eastward. Thus, we will run with POPs varying from 30-40% in the western Piedmont to 20% near US-1. Temperatures continue to be a tough call, especially in the western Piedmont, as a southeasterly wind has developed, but the moisture (stratus) is somewhat trapped horizontally but the mountains and vertically by a weak CAD-like inversion (per 12z GSO raob). However, 850/925mb temps are around 16-18C over the southern and western portions of the Piedmont, so the airmass will support strong warming if/when clouds breaks. We`ve blended in some HRRR and LAMP guidance to help with the uncertainty and possible gradient, which yields mid 70s northeast to mid 80s southeast. Tonight: Sfc cold front is forecast to slip east of the mountains, but remain west of the forecast area through daybreak Tuesday. Upper support is almost non-existent, so expect convection to be tied closed to the low-level moisture convergence along the front and thus expect bulk of shower activity to remain across the NC Foothills and Western Piedmont. Lows in the mid 60s to lower 70s. && .SHORT TERM /TUESDAY AND TUESDAY NIGHT/... As of 415 AM Monday... Low-level frontal zone stretched across central NC will slow down, potentially temporary stall across the area as the closed upper low over the Great Lakes and attendant deep upper trough begins to digs south into the Ohio Valley and southern Appalachians. Axis of 1.6- 1.7" PWAT attendant to the front will be centered across the area Tuesday afternoon and Tuesday night with numerous showers and scattered thunderstorms expected to move slowly south-southeastward across the area. Weak mid-level lapse rates should again limit destabilization and thwart severe threat. We could however see some locally heavy rain and minor flooding with models suggesting rainfall amounts widespread rainfall amounts of a half inch to an inch, with locally higher amounts of 1 to 1.5 inches possible. The front should settle slowly across eastern portions by late Tuesday evening/night with rain chances beginning to taper off from nw to se by daybreak Wednesday. Highs in the mid 70s northwest to lower 80s se. Lows Tuesday night 60 to 67. && .LONG TERM /Wednesday through Sunday/... As of 345 AM Monday... Forecast confidence remains below average due to an atypically complex synoptic pattern expected to evolve over North America mid/late week. The 00Z GFS/ECMWF both indicate that an upper level low amplifying over the Great Lakes early this week will dig southward through the OH valley and cut-off in vicinity of the TN Valley/Mid-Atlantic through mid/late week as an expansive upper level ridge builds over the eastern 2/3 of North America, though disagreement persists w/regard to the precise evolution of the cut- off low. Broadly speaking, long range guidance supports above normal chances for cloud cover/precipitation and slightly below normal temperatures mid/late week, though further details (i.e. precip amount/timing and perhaps severe wx potential) remain difficult to ascertain at this time. -Vincent && .AVIATION /18Z MONDAY THROUGH FRIDAY/...
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As of 140 PM Monday... Stratus is slowly eroding from south to north, leading to VFR at RWI AND FAY, and should yield VFR at RDU by 19Z and GSO/INT by around 21Z. Scattered shower and a few storms will move into the vicinity of GSO/INT this evening, with showers possible throughout the night as a slow moving cold front inches into NC from the west. Most, if not all of the showers will remain west of RDU. If winds are light enough, some MVFR or IFR vsbys are possible at FAY and RWI overnight, though confidence is low. The front and associated showers will continue to shift slowly east on Tuesday, focusing more in the vicinity of RDU by midday. MVFR or VFR conditions are expected to be predominate. Looking beyond the 24 TAF Period: The combination of the stalled front and an upper low over the Tennessee Valley will continue the unsettled weather Tuesday night and Wednesday. Conditions are expected to improve to VFR from northwest to southeast by Wednesday night as drier air filters into the area.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL/BS SHORT TERM...CBL LONG TERM...Vincent AVIATION...BS

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