Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 130025 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 825 PM EDT Thu Oct 12 2017 .SYNOPSIS... A backdoor cold front will settle south of North Carolina tonight. Behind the front, a cool high pressure area will build down the East Coast through Saturday. && .NEAR TERM /THROUGH TONIGHT/... As of 215 PM Thursday... The backdoor cold front will continue pushing south of the forecast area tonight, with a cooler high pressure area pushing in from the NNE, generating a cold air damming regime. Water vapor imagery confirms abundant drying in the mid and upper levels behind the broad mid level trough pushing SE off the New England coast, and this, along with a southward push of a subtle shear axis south of the area, has contributed to the lack of precip over the area today. But a little heating across the south has pushed MLCAPE up to 1000 J/kg, and we`re likely to see scattered showers and isolated storms over far southern sections through the rest of the afternoon. The low level northeasterly flow from 850 mb down to the surface will continue to draw in abundant low level moisture into the area through tonight. Low level moist isentropic upglide will increase and deepen tonight with nocturnal stabilization, so what is now very patchy and extremely light drizzle should increase in coverage overnight, and will indicate a trend toward widespread light drizzle, particularly over the Piedmont. The best chance of larger hydrometeors leading to measurable amounts will be over the NW Piedmont, where upglide atop the heart of the stable pool should be greatest. Expect lows from 61 far N to 68 SE. -GIH && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 315 PM Thursday... The damming wedge will hold in place through central NC through Fri and Fri night, with low level stability reinforced by an anticyclone just above the surface-based stable pool extending through the mid levels. Heating will result in some lifting and breaks in the stratus through the day across the southern and eastern sections, along the shallower edges of the wedging ridge. Isentropic upglide wanes during the morning, leaving just small chances of patchy light rain through the day, mainly in the NW. Low level thicknesses will still be slightly above normal, but with the cloudiness, highs should be closer to normal, from around 70 N to upper 70s to near 80 far SE. Shallow fog is possible Fri night, as a lack of clouds aloft allows for good radiative cooling down to the dewpoint within light winds. Lows 59-65. -GIH && .LONG TERM /SATURDAY THROUGH THURSDAY/... As of 245 PM Thursday... Wedge airmass will be cut off from reinforcing cool air advection as the surface ridge progresses offshore well east of the Mid Atlantic. As such, the cool air will be undergoing modest erosion from the top down, and the south and east may break out during the afternoon. Deeper cool and moist axis across the western Piedmont will likely hold the cloudiness in all day, with highs stalling in the mid 70s in the northwest while the southeast reaches low to possibly mid 80s. Return flow will be underway as the cooler airmass will be scoured and mixed out by Sunday, with highs rebounding to the low and mid 80s. Latest GFS is ~6 hours faster bringing our long awaited cold front across the mountains Sunday night. This timing difference won`t be a huge concern, as the front will be moving quickly and be strongly sheared, which will just about eliminate any Gulf connection to provide additional moisture advection. In addition, instability will be very low as well due to the fronts moving through early in the day, so potential for strong convection will be very limited and confined to the southeast in the early afternoon. Cold air advection will be underway early as well, with highs barely reaching 70 in the northwest, with some very low 80s southeast. Cool high pressure settles in Monday night through midweek...with highs Tuesday and Wednesday mostly in the mid 60s north to very low 70s south...warming a bit by late week to the low and mid 70s as the airmass modifies. Mins will be downright chilly....falling mostly to the mid and upper 40s each morning from Tuesday through Thursday. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/...
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As of 810 PM Thursday... 24 Hour TAF Period: Adverse aviation conditions are expected to continue through the 24 hour TAF period, as a CAD airmass encompasses all of central NC. This will lead to east to northeasterly low level across the area with lowering cigs overnight. Expect cigs will fall in to the IFR category later this evening/into early Friday morning, with even some LIFR cigs early Friday/Friday morning. Patchy drizzle and light rain will also be possible tonight into Friday, with the best chance at KGSO/KINT. Cigs will slowly increase some on Friday, though likely remaining IFR at KGSO/KINT and MVFR at KRDU. Cigs may briefly rise late in the day at KFAY AND KRWI to VFR. Outlook: IFR/LIFR conditions should return for Fri evening through much of Sat morning. Slow improvement of cigs through the MVFR category to low-end VFR is expected Sat afternoon. Sub-VFR conditions may return late Sat night through daybreak Sun but won`t be as thick or long-lasting as tonight`s poor conditions. VFR conditions are expected Sun, but a strong cold front pushing through Sun evening will bring sub-VFR conditions Sun night through early Mon. Improvement to VFR is expected during Mon, with clearing skies Tue.
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&& .CLIMATE... Record high minimum temps for October 12: GSO: 64 in 2002 RDU: 68 in 1990 FAY: 68 in 1990 && .RAH WATCHES/WARNINGS/ADVISORIES... None. $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...mlm AVIATION...BSD/Hartfield CLIMATE...MWS

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