Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 260817 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 415 AM EDT MON SEP 26 2016 .SYNOPSIS... A quasi-stationary front across southwestern NC will return north as a warm front tonight 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 345 AM Monday Today: Southerly moist upglide/weak WAA atop a quasi-stationary frontal boundary that extends across the western piedmont/foothills will support a small chance of showers across the TRIAD this morning. The shower activity should dissipate into sprinkles as it encounters the low-level ridge axis and associated drier and stable air in place across the eastern piedmont and coastal plain. The parent high anchoring this low-level ridge axis down the Mid-Atlantic Coast will quickly move offshore today in advance of a cold front and northern stream trough moving into the central and southern Appalachians. This will allow the quasi-stationary frontal boundary over the western piedmont to retreat northeastward throughout the day, paving the way for warmer air just to our southwest to spread ne. Yesterday, we saw temperatures in the warm sector across the southwestern piedmont soar into the lower 90s. While low-level cloud cover should temper temperatures reaching these levels today, expect to see a sharp SW to NE temperature gradient with temperatures ranging from lower to mid 80s southwest to lower/mid 70s northeast, highly sensitive/dependent to the exact timing of the retreating warm front. With weak to moderate instability developing as the warm air spreads north and maximized across the foothills and western piedmont, the better convective rain chances this afternoon/early evening will remain confined to western portions of the forecast area. Weak deep-layer shear and poor mid-level lapse rates will limit severe potential. 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/...
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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.
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&& .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 /06Z MONDAY THROUGH THURSDAY/... As of 115 AM Monday... IFR to MVFR ceilings are expected overnight, lowest at KINT and KGSO in closer proximity to a a quasi-stationary frontal boundary that extends across the western/southern piedmont. Additionally, sely moist upglide atop a quasi-stationary frontal boundary will support a small chance of showers over the TRIAD overnight and into the morning hours. Any sub-VFR conditions in the east(KRWI and KFAY) should become VFR by 14 to 15z, with KRDU expected to become VFR between 15 to 18z. Ceilings will be much slower to improve at KGSO and KINT, with MVFR or low end VFR lingering into the afternoon 18 to 21z time frame. Moisture pooling ahead of a cold front moving into the mountains will also support a small chance of showers and possibly a thunderstorm late in the afternoon/early evening with rain chances increasing overnight with sub-VFR ceilings as the front approaches the NW Piedmont. Looking beyond the 24 TAF Period: A cold front will move very slowly se through the area Tuesday and into the day on Wednesday. Showers and storms with associated periods of sub-VFR conditions are expected to accompany the front. Conditions are expected to improve to VFR from northwest to southeast Wednesday-Wednesday night as drier air filters into the area. During midweek, a rather unsettled pattern is expected to evolve as a deep upper low sags southward from the Great Lakes into the Central Appalachians. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...CBL LONG TERM...Vincent AVIATION...CBL is the U.S. government's official web portal to all federal, state and local government web resources and services.