Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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073 FXUS62 KRAH 121522 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1022 AM EST Tue Dec 12 2017 .SYNOPSIS... A pair of dry cold fronts will cross central North Carolina today. Cold high pressure will build in tonight through Wednesday. A fast moving upper level disturbance will move through the region Wednesday night. && .NEAR TERM /today through tonight/...
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As of 1022 AM Tuesday... As of 10 AM...the initial cold front was analyzed in sfc obs moving across the Triad. It will continue moving east and will cross the rest of our CWA by early afternoon. As the upper BL and mid levels cool, we`re likely to see some shallow cu develop, but given the overall dry airmass preceding it, we are expecting the weather to stay dry today. The midlevel trough axis, and secondary sfc front assoc with the more potent surge of colder air, is now crossing the Ohio River Valley. The secondary front, ushering in the surge of colder air, is expected to arrive this evening. In terms of temps the rest of today... behind the first front temps may rise only a few more degrees (highs in the upper 40s), while east of the front we should see temps climb into the lower-mid 50s for highs today. No signif changes with the morning update. Prev disc as of 255 AM Tuesday...High and mid clouds have begun streaming SW to NE across the CWA on schedule, along a mid level speed max ahead of the approaching trough and initial surface front. This mid level jet and leading cold front will shift east off the coast by mid afternoon, leading to a decrease in mid/high clouds but an increase in flat cu with the onset of deep mixing. Overall, skies should average out partly to mostly cloudy. Post-front surface winds will veer to WNW and NW and surge to 12-16 kts with gusts to 22-28 kts, and perhaps periodically higher. A secondary uptick in winds will arrive with the next reinforcing cold front late in the day, which will bring the substantially colder air. With the mountains serving to delay the onset of strong cold air advection, high temps should still be within a couple degrees of normal, from the upper 40s to near 50 NW to the mid-upper 50s SE. Much colder and drier air will start to pour in by mid to late afternoon, with clearing skies toward nightfall. Dewpoints will fall through the 20s and teens overnight, as temps bottom out in the 20-26 range, with perhaps some upper teens in outlying areas. We will stay mixed through the night, so expect sustained winds to stay up around 7-14 kts overnight, with sporadic gusts to 15-22 kts possible, mainly across the N and E. Morning wind chills should drop to 10-20 degrees. -GIH
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&& .SHORT TERM /Wednesday through Wednesday night/... As of 320 AM Tuesday... A chilly day with thicknesses starting out 45-55 m below normal, suggesting highs from the upper 40s to mid 40s N to S despite mostly sunny skies. A fast moving clipper that will be dropping over the Midwest early Wed will dive through the Mid Atlantic region Wed evening, followed immediately by a second potent wave passing by further north late Wed night. The initial and more southern-track wave will bring a batch of scattered to broken mid clouds across the area Wed evening, with the greatest cloud cover across the northern sections of NC. This moisture aloft may be deep enough and the attending DPVA strong enough to generate some precip, although the subcloud layer should be too dry for much (if any) of this to reach the ground, given the expected large surface dewpoint depression. Have opted to mention a brief period of possible flurries across the far N, between Roxboro and Roanoke Rapids, Wed evening. Skies should trend back to fair after midnight as the wave departs. Lows from the mid 20s to around 30. -GIH && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 AM Tuesday... Predominantly zonal flow aloft mid week will slowly transition to weak troughing in the east by mid day Friday. Several waves of energy will rotate along the trough axis out of the upper mid west during the long term period. The first system should pass just to our north Thursday morning, introducing only a short period of enhanced cloud cover to the northern piedmont counties. A second, much stronger wave, will rotate around a digging trough axis Friday night into Saturday, bringing a surge of much cooler temperatures and enhanced POPs to the area. This wave looks to initiate the frontogenesis process just off the VA/NC coast, keeping most of the precipitation offshore. This trend will be worth keeping an eye on though, as faster development could see POPs sneak a bit further west into our coastal plain counties. A brief period of high pressure builds in from the south Saturday into early Sunday, allowing southerly to southwesterly flow, along with near normal temperatures to reestablish ahead of an approaching cold front set to move through early Monday. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... As of 645 AM Tuesday... High confidence in VFR conditions for the next 24 hours across all of central NC. But a surge of strong and gusty winds today may lead to handling difficulties with aircraft this afternoon through tonight. A dry cold front and potent upper level trough will cross the area today, bringing a period of VFR cigs with cloud bases over 5,000 ft AGL and unrestricted vsbys. Surface winds will veer from SW to WNW and NW with frontal passage, occurring around 14-15z at INT/GSO and 15z-18z at RDU/RWI/FAY. Sustained speeds post-front of 12-17 kts, with gusts to 22-28 kts, are likely, continuing through much of tonight as colder air pours into the area. Surface winds will decrease overnight and back to WSW by daybreak Wed. Looking beyond 12z Wed, VFR conditions will hold through Wed, then the approach and passage of an upper level disturbance across VA and northern NC may bring a period of cigs (likely VFR but may be briefly high-end MVFR) Wed night with a possible flurry. VFR conditions should then dominate Thu through Sat, although yet another disturbance may bring a period of MVFR cigs Fri. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...np/Hartfield SHORT TERM...Hartfield LONG TERM...JJM AVIATION...Hartfield

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