Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 140611 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 110 AM EST Sat Jan 14 2018 .SYNOPSIS...
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Chilly high pressure will extend across the Carolinas today and tonight. The high will retreat to our northeast Monday, bringing more seasonable temperatures to our region on Tuesday. A strong upper level trough will cross the region Tuesday night through Wednesday night.
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&& .NEAR TERM /THROUGH TONIGHT/... As of 740 PM Saturday... Stratocumulus layer is thinning as it tries to spread south and west concurrent with the dry surface ridge oozing down the Atlantic seaboard. Have made some tweaks to current coverage and trend towards clear by sunrise per forecast soundings off the HRRR and RAP. Dew points are running a couple of degrees below forecast, so some minor tweaks there. Otherwise...steady as she goes. Previous Discussion: A complication has popped up for this evening`s forecast. The surface trough is currently moving SE of the forecast area, with periodically gusty NW winds and falling dewpoints in its wake. Meanwhile, another low level boundary, evident on high-res visible satellite imagery, extends from south central VA along the Roanoke River basin southeastward to the central Outer Banks, pushing toward the S and SW. Stratocu lingers both ahead of and behind this feature, within a diffuse front and zone of weak low level convergence evident at 900-850 mb, and we`re even seeing some spotty light rain and drizzle at Ahoskie in the last hour. This moisture is trapped beneath a growing subsidence inversion aloft and near the top of a well-mixed surface-based layer, and with weak flow through that layer, it`s lacking any opportunity to disperse horizontally, too. The GFS has been consistently showing this deck of clouds pushing SSW into central NC through this evening, and now the recent HRRR runs depict it as well, even showing deep enough moisture for a little precip at the ground over the NE Piedmont around mid evening. And based on the HRRR forecast soundings, with little to no ice in the cloud and with falling surface wet bulbs as colder air rushes in, whatever falls may transition from patchy drizzle to patchy freezing drizzle in some areas. In any case, anything that might make it to the ground would be extremely light and short-lived. Have added a brief period of patchy drizzle along this feature from now through mid evening from the NE CWA southwestward through the central Piedmont. Otherwise, expect partly to mostly cloudy skies over the N and E CWA through evening, trending toward gradual clearing overnight as drier air is entrained in the low levels. Lows 20-26, with some teens likely in the normally colder areas. -GIH && .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 240 PM Saturday... The weakening mid level shear axis will be heading to our east Sun morning, as the cold surface high noses in from the N. The column is projected to be stable and quite dry, and expect plenty of sunshine Sun. Taking the 925 mb parcel down to the surface dry adiabatically yields highs of 33-41, very close to the earlier forecast and statistical guidance. A slug of moisture aloft and weak mid level DPVA arrives late Sun night from the SW, so expect a few high clouds to streak into the area from the SW overnight. Lows 14-20. -GIH && .LONG TERM /MONDAY THROUGH SATURDAY/... As of 230 PM Saturday... A initially strongly positively-tilted, and similarly strongly meridional trough aloft, will pivot across the MS Valley Mon-Tue, then to the East Coast while assuming a neutral tilt, by Wed-Thu. Forecast details in the Tuesday night to Wednesday period continue to evolve with latest model guidance. At the surface, increasingly modified Arctic high pressure will be in the place from Atlantic Canada to the sern US early next week, while an occluding clipper low will have migrated to the Great Lakes through Tue. Along the trailing Arctic front, an initially flat, triple point wave will meanwhile develop from the mid MS Valley to the cntl Appalachians through Tue. A warm front preceding the triple point is expected to cross cntl NC Mon night, but not manifest as a noticeable increase in surface temperatures until diurnal heating on Tue. The Arctic boundary is then forecast to collapse east of the Appalachians and across cntl NC Tue night, with following Arctic high pressure that will build into, and modify over, the sern US through the end of the week. Strong jet dynamics and deep layer frontogenesis accompanying the upper jet/front and related low level frontal zone should be sufficient to support at least a light precipitation event over cntl NC Tue night-Wed. That precipitation would likely fall in the form of light rain or rain mixed with snow early Tue night, since temperatures will have warmed considerably, into the upr 40s to lwr 50s for most Tue afternoon; and the models are typically too quick in surging cold air masses east of the cntl Appalachians of VA/NC. However, partial thickness values and boundary layer temperatures are both forecast to become supportive of a west to east changeover to snow late Tue night into Wednesday. If the trough aloft is weaker and more positively-tilted as it approaches NC, then a light rain, to inconsequential snow event would result. Temperatures are expected to otherwise turn colder by Wed, before moderating to around or slightly above seasonal normals by the end of the week. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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As of 110 AM Sunday... There is a high likelihood of VFR parameters across central NC through 12Z Monday. Chilly high pressure at the surface will continue to build into central NC today. Nly sfc winds 7-12kts will occur with infrequent gusts 15-18kts probable, especially between 14Z-18Z, and mostly in vicinity of KRWI, KFAY, and KRDU. Sfc winds will subside to near cal by sunset. and remain light and variable on Monday. VFR parameters should continue through late Tuesday. An upper level trough will increase the cloudiness late Tuesday through Wednesday, lowering cloud bases to low end VFR and possibly high end MVFR close to daybreak Wednesday. Ceilings should lift/dissipate Wednesday night into Thursday as central NC experiences subsidence/sinking air in the wake of the departing upper level trough.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...Hartfield/mlm SHORT TERM...Hartfield LONG TERM...MWS/Franklin AVIATION...WSS

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