Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201821 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 215 PM EDT Fri Oct 20 2017 .SYNOPSIS... A ridge of high pressure will extend across the eastern United States through the weekend. && .NEAR TERM /THROUGH TONIGHT/... As of 1015 AM Friday... Stacked high pressure over the Deep South/TN Valley will maintain dry and seasonably mild air mass over central NC this afternoon and tonight. The circulation around this high pressure system is resulting in a nw flow over our area. The downslope component of the low level flow along with modest compressional warming aloft will lend to a relatively warm afternoon with temperatures well into the 70s, and likely reaching 80 degrees across the southern Piedmont and the Sandhills. Presence of the low level dry air over the region will once again allow temperatures to cool quickly immediately after sunset, falling through the 60s in the early evening, and into the 50s by late evening. Overnight low temperatures in the 45-50 degree range. && .SHORT TERM /SATURDAY AND SATURDAY NIGHT/... As of 350 AM Friday... Mid-upper ridging will linger in the vicinity of the sern US coast, while high pressure drifts off the middle Atlantic and Northeast coast, while also strengthening. The result will be a generally persistence forecast, though with an increase in high cloudiness that may tip sky conditions into the partly cloudy range by Sat night, with associated slightly milder low temperatures in the upper 40s to middle 50s. High temperatures again in the middle 70s to around 80 degrees, or so. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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As of 215 PM Friday... Ridging over the Atlantic coast will shift east and offshore Sunday as a trough over the Mississippi Valley deepens and a cutoff low forms over the lower Mississippi valley. Another near perfect "final fair" day is on tap, with mostly sunny skies and highs climbing to the mid and upper 70s. Warm air advection will keep mins up overnight, with Monday morning`s lows mostly in the mid and upper 50s. Clouds will be on the increase Monday as deepening south to southwest return flow pumps moisture into the area ahead of a strong cold front which will be reaching the mountains late in the day. It will be warm ahead of the front in southerly flow with at least some filtered sun early in the day, and highs will reach the mid and upper 70s. Expect scattered showers showers to develop over the Piedmont, especially in the Charlotte and Triad areas, during the afternoon, with showers becoming likely Monday night as the front pushes across the mountains and accelerates eastward. Mins ahead of the front again will remain mild Monday night...from upper 50s west to the lower 60s east. There are model differences in the timing and evolution of the cutoff low, which will determine mid level dynamics available to support strong low level forcing ahead of the surface frontal zone. Even given unfavorable timing=lessened instability, low level jetting of 50+ knots and strong helicity ahead of the front suggest a line of vigorous showers/thunderstorms late Monday night in the west shifting to the Coastal Plain towards mid day Tuesday. Highs Tuesday will be hampered somewhat by cloudiness, with temperatures topping out near 70 in the west to 75 in the southeast. Cold air advection begins to surge into the area Tuesday night, with dry weather returning, though we could see lingering instablity showers as residual moisture is squeezed out of the airmass. Mins Wednesday morning will range from 45 to 50, with highs Wednesday mostly in the low and mid 60s. Cool air peaks on Thursday, with morning lows mostly from 40 to 45, with some upper 30s in the northwest. Highs will be mostly in the lower 60s with some upper 50s northwest. Friday will warm a bit to the mid and upper 60s as short lived surface high pressure moves offshore and low level flow quickly backs from northwest to southwest.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... As of 145 PM Friday... There is a high probability that VFR conditions will persist across central NC through 00Z Sunday as high pressure at the surface and aloft controls the weather across central NC. The exception will be brief instance of MVFR/IFR fog in vicinity of KRWI and possibly KFAY between 06Z and 12Z Saturday. Otherwise expect clear-mostly clear skies and light winds, primarily out of the east-northeast, except calm at night. The good aviation conditions are expected to persists through early Sunday evening. Later Sunday night and on through Tuesday, an approaching frontal system will draw a moist low level air mass into central NC leading to an increased threat for sub VFR ceilings as well as increasing coverage of showers and a few thunderstorms, especially late Monday through Tuesday. Improving aviation conditions anticipated Wednesday as the front exits our region and chilly high pressure expands toward the Carolinas. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...WSS SHORT TERM...MWS LONG TERM...mlm AVIATION...WSS

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