Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 121846 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 245 PM EDT Thu Oct 12 2017 .SYNOPSIS... A backdoor cold front will settle just south of the state 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 the low level northeasterly flow from 850 mb down to the surface will continue to draw in abundant low level moisture 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 tonight from 61 far N to 68 SE. -GIH && .SHORT TERM /FRIDAY AND FRIDAY NIGHT/... As of 310 AM Thursday... The cold air damming air mass is expected to hold as the parent high over New England continues to build southward into the southern Appalachians. While the isentropic upglide slacks off, reducing the threat for light rain/drizzle, extensive low clouds will persist. This limiteds insolation should yield temperatures notably cooler compared to the past few days, ranging from near 70 in the nw Piedmont where the low clouds will persist all day to the upper 70s in the southeast where partial sun may occur in the afternoon. The dreary conditions will persist into Friday night with extensive cloudiness and patchy drizzle and areas of fog developing. It will remain relatively mild overnight with min temps generally in the 60- 65 degree range. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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As of 245 PM Thursday... Wedge airmass will be cut off from reinforcing cool air advection as the surface ridge progesses 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.
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&& .AVIATION /18Z Thursday through Tuesday/... As of 155 PM Thursday... Adverse aviation conditions will dominate central NC TAF locations through the next 24 hours. A backdoor cold front will settle south of the forecast area late this afternoon, where it will hold stationary through Fri and beyond. Plentiful low level moisture and a steady low level wind flow from the NE will keep skies broken to overcast, with mostly MVFR cigs through sunset, falling to IFR/LIFR this evening and lasting through sunrise Fri with areas of light rain and drizzle, especially at INT/GSO which may see several hours of IFR/LIFR vsbys/cigs in drizzle overnight. Slow improvement to MVFR cigs (but VFR vsbys) is expected starting soon after 15z Fri, with MVFR as the most likely condition areawide through the end of the TAF valid period. Looking beyond 18z Fri, there may be some improvement to VFR (most likely at FAY) Fri afternoon, however MVFR cigs and VFR vsbys will dominate much of central NC through sunset. 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. -GIH && .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...WSS LONG TERM...mlm AVIATION...Hartfield CLIMATE...MWS

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