Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 131907 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 205 PM EST Sat Jan 13 2018 .SYNOPSIS... Chilly high pressure will build into the Carolinas through the rest of the weekend. This high will retreat to our northeast Monday, bringing more seasonable temperatures on Tuesday. A strong upper level trough will cross the region Tuesday night through Wednesday night. && .NEAR TERM /THROUGH TONIGHT/...
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As of 205 PM Saturday... 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
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&& .SHORT TERM /SUNDAY AND SUNDAY NIGHT/... As of 310 AM Saturday... 850mb thermal trough resides immediately to our NW Sunday and Sunday night while sfc high pressure builds into the region. While expecting a good deal of sun, afternoon temperatures will be 12-15 degrees below normal, generally in the 35-40 degree range. With the sfc ridge projected to be overhead Sunday night, sfc wind will decouple around sunset. Temperatures will cool quickly in the cold dry air mass, so expect minimum temperatures by early Monday morning between 15 and 20 degrees. The normally colder locations in the Piedmont will likely be in the 10-15 degree range. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 415 AM Saturday... Medium range guidance remains in good agreement regarding the development and slow ewd progression of highly amplified flow aloft across the CONUS this period. Within this pattern, an 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. While some timing and amplitude details remain, spread in 00Z guidance is much less than 24 hrs ago. 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. Regardless of whether or not a closed low forms within the aforementioned meridional trough, 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 Tue night-Wed morning. This system certainly has the potential to produce measurable snow over the middle Atlantic states, including cntl NC, but forecasting such an occurrence with any degree of confidence at this time range would be premature. Indeed, if the trough aloft is weaker and more positively-tilted as it approaches NC, then a light rain, to inconsequential flake event would result. Stay tuned. Temperatures are expected to otherwise turn colder by Wed, before moderating through the end of the week. && .AVIATION /18Z Saturday through Thursday/... As of 1245 PM Saturday... Lingering MVFR cigs at FAY will exit the area in the next hour or so, as the low level front pushes E and SE of central NC. Otherwise, VFR conditions will be the rule across central NC over the next 24 hours as chilly high pressure begins to build into the area. Lingering moisture at 3500-5000 ft AGL spilling SSW into NC from VA late tonight may bring scattered to briefly broken flat VFR clouds for a couple of hours this evening, but otherwise skies will remain mostly clear. Surface winds will be mainly from the NW or NNW into this evening, with periodic gusts to around 15-25 kts, becoming northerly and diminishing a bit tonight into Sun morning. Looking beyond 18z Sun, chilly high pressure will extend into the region through Mon, with VFR conditions. Next chance for sub-VFR conditions will arrive Tue into Wed as a potent upper level trough slowly crosses the region. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...WSS LONG TERM...MWS AVIATION...Hartfield

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