Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 141447 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 945 AM EST Sun Jan 14 2018 .SYNOPSIS... 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. && .NEAR TERM /THROUGH TONIGHT/...
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As of 945 AM Sunday... Forecast looks good. Aside from shallow moisture around 850 mb beneath the inversion aloft noted on the 12z GSO sounding, dry air is in place and upstream, so expect little more than a few flat cu and wispy high clouds today as subsidence dominates. Despite the abundant sunshine, low level thermal profiles and cold air advection today support highs of just 33-40, 15-20 degrees below normal highs for this time of year. Gusty winds from the NNE should continue into the afternoon before slowly decreasing late, as the MSLP gradient slackens. -GIH Earlier discussion from 300 AM: Chilly high pressure centered over the northern Mid-Atlantic and New England will extend south into central NC today and tonight. 00Z upper air analysis at 850mb depicts a deep thermal trough over the eastern half of the nation with the 0 degree isotherm well south into south Texas and the northern Gulf. Nly low level flow will maintain cold air advection over central NC today. This cold air advection already evident by pre-dawn temperatures in the 20-25 degree range across the Piedmont. With early morning temperatures likely starting in the 17-23 degrees range, even a 15 degree temperature recovery translates to afternoon temperatures just above freezing across the northern counties, and mid-upper 30s across the south. While skies will be sunny-mostly sunny through most of the day, an approaching weak upper level s/w may result in patchy high clouds streaking in from the sw late in the day. Tonight, aside from brief periods of thin/patchy mid and upper level clouds, expect clear/partly cloudy skies and a very dry/cold low level atmosphere. Currently think that clouds aloft will be too thin to have much affect on our temperatures so will lean toward the cool side of guidance. Min temps 15-20, with 10-15 above at the normally colder spots in the Piedmont.
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&& .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 300 AM Sunday... Monday and Monday night, sfc ridge weakens but will maintain an orientation south southwest-north northeast across central NC. This will maintain the bone dry air mass in the lower levels of the atmosphere. 850mb flow attains a wly direction Monday, initiating warming in the lower atmosphere. Aloft, wly flow will begin to stream moisture ahead of a shear axis crossing the mid MS/lower OH Valley. Thus, expect periods of filtered sunshine through the veil of high clouds, particularly across the western Piedmont. Although we will start out quite cold, the moderating atmosphere and developing wly flow will aid to boost afternoon temperatures into upper 30s/around 40 NW to the low-mid 40s SE. The moderating air mass continues Monday night under mostly clear/partly cloudy skies. Min temps generally 20-25 degrees, though slightly colder in the outlying areas of the Piedmont. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 355 AM EDT Sunday... The initial inland sfc low associated with the high amplitude positive-tilted trough over the NE-central US will fill over the Eastern Great Lakes/NE US late Tuesday-Tuesday night, eventually giving way to a series of coastal low development along the Mid- Atlantic Coast Wednesday-Thursday as the potent upper trough assumes a neutral tilt as it pivots east across the region. There continues to be a large model spread WRT to the timing and strength/amplification of the trough and it`s associated ana-frontal precip band, driven by strong shortwave dynamics and f-gen that`s progged to move west-east across central NC late Tuesday night and into the day on Wednesday. Operational versions of the EC and GFS, have trended drier with liquid equivalent amounts over the past several runs. Meanwhile, the GEFS and EPS avg mean liquid QPF is generally around a 0.10" across much of the area, with slightly higher amounts of near 0.20" across the far northern/VA bordering counties. With afternoon temps on Tuesday expected to moderate into the 45 to 50 degree range Tuesday afternoon ahead of the attendant sfc cold front, current timing and thermal profiles, still supports precip starting as rain or a rain-snow mix at onset Tuesday night with west to east change-over to snow early Wednesday morning and into the afternoon(east)as the expansive Arctic High builds in from the west. As previous forecast discussions have noted, one model pitfall and potential forecast concern is that NWP models tend to advect low- level cold air east of the mountains too quickly, which in itself can be a self limiting process as considerable dry sub-cloud layers develop. Given continued high uncertainty, will make only minor changes to current forecast. Stay tune. The Arctic blast is very strong but short-lived with H8 temps progged to crash to -12 to 13C Wednesday night as the parent high settles over the Gulf Coast region. Highs generally in the 30s both Wednesday and Thursday, with quick moderation as temperatures return above normal by the weekend. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... As of 640 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 16-20kts probable, especially through 18Z, and mostly in vicinity of KRWI and KFAY. Sfc winds will subside to less than 10kts 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. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...Hartfield/WSS SHORT TERM...WSS LONG TERM...CBL AVIATION...WSS

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