Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 032026 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 323 PM EST Sat Dec 3 2016 .SYNOPSIS... High pressure will continue to build SE into the region tonight. The high pressure will extend from NY state south through the Carolinas Sunday, as a coastal front develops. A storm system will move from the Gulf Coast states into the Southeast states early in the week increasing the chance of rain. && .NEAR TERM /THROUGH SUNDAY/... As of 323 PM Saturday... First CAD event in quite a while expected to develop Sunday afternoon, with some rain and chilly temperatures. The 1028 MB surface high pressure extending from the Great Lakes SE through the Ohio Valley and into the central Appalachians will continue to move east to a position along the eastern seaboard Sunday. Dry and cool weather is expected overnight as high cloudiness is forecast to continue to overspread the region from the southwest. This increase in clouds is in response to the SW to NE mid/upper level jet extending across the southern tier of the U.S (out ahead of the deep western U.S. trough). This mid/upper level trough is forecast to lift NE during the next few days. In response, the surface high will shift east tonight and will extend down the eastern seaboard Sunday. This should set the stage for the onset of a Cold Air Damming (CAD) episode over the Piedmont Damming Region later Sunday. This will be partly dependent on enough rain (QPF) to allow for evaporative cooling of the low level dry air in place. Models are in general agreement in a tenth to a quarter inch of rain in the Piedmont Sunday and Sunday evening, which should lead to hybrid CAD conditions. This first shot of rain will occur with the approaching disturbance aloft Sunday leading to an initial wave of low pressure (weak) that is forecast to track SW to NE near the coastal or developing CAD boundary later Sunday and Sunday evening. For tonight, expect increasing cloudiness with a light north breeze less than 10 mph. Lows generally 35-40. A few sprinkles possible late in the west. Sunday the WAA moist flow from the surface to H85 and developing mid level lift will lead to light rain developing/spreading NE across the region. Timing should bring highest POP to the west during the early to mid afternoon spreading throughout the entire region during the late day and Sunday night. Highs Sunday will be dependent on onset of rain and the amount of rain in the damming region. For now, we expect a general 0.25 to 0.50 Sunday and Sunday night. Highs should hold in the 40s Piedmont, with 50s SE. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... As of 323 PM Saturday... Rain on Sunday night will taper to light rain or drizzle late as the surge of lift shifts to our NE and the initial wave of low pressure is forecast to move NE off the coast by 12Z/Monday. This will cut off the rain and bring a break in the rain chances for most of Monday. This occurs as another (this time weaker) surface high builds in from the north Monday and Monday night. Some residual affects of the CAD should linger Monday in the heart of the Piedmont as winds will be light NE with the lack of a good pressure gradient. Low clouds early may give way to breaks in the clouds around the edges of the damming Monday afternoon. However, we will undercut highs Monday going below statistical guidance by 5 degrees in the W-N Piedmont (near 50), but go close to guidance where breaks should occur (Sandhills, Coastal Plain) may see lower 60s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... As of 325 AM Saturday... Tuesday the Miller B scenario takes full effect a pair of lows on either side of the wedge parked over the Piedmont. Precipitation should begin early Tuesday morning and continue all the way through Tuesday night before the system starts to move off to the northeast. Accumulations for this event should be over an inch and possibly up to two inches. Temperatures will be tricky and dependent highly upon the track of the coastal low. With fairly high confidence, the Triad should stay cold throughout the day under the wedge with highs possibly only in the upper 40s. The bigger uncertainties in the temperature forecast lay in the south and east where highs could be as much as 60 degrees. Wednesday and Thursday will be dry and a little warmer on the front side of a longwave trough bisecting the continent. Highs in the 60s. By Thursday night, models begin to diverge on timing and available moisture leading to two very different possible scenarios for Thursday night into Friday. The GFS solution has a very progressive trough and a drier solution which brings very cold temperatures into the area on Thursday night. The ECMWF solution is slower and wetter which means warmer temperatures hanging around longer Thursday night. For now we are taking the dry, colder forecast so expect temperatures below freezing both Thursday and Friday nights with Friday being the coldest as very anomalous thickness values move into the area and bring low temperatures down into the 20-25 degree range. && .AVIATION /18Z SATURDAY THROUGH WEDNESDAY/... As of 1240 PM Saturday... High confidence in VFR conditions through around 09Z/Sunday, then CIGS will lower between 09Z-18Z Sunday into the MVFR range west. VSBYS remain VFR with a chance of light rain arriving around 12z in the west, then most likely after 18z/sunday in the east. OUTLOOK FOR LATE SUNDAY THROUGH WEDNESDAY. Confidence is high that conditions will become IFR to LIFR Sunday evening/night and remain into Monday with periods of rain and drizzle. LIFR TO IFR conditions are expected Monday night and Tuesday with the storm system arriving from the SW and the cold air damming over the region. Rain should taper off Tuesday night but IFR/LIFR conditions may hold through daybreak Wednesday, followed by improvement to VFR by midday Wednesday. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Badgett NEAR TERM...Badgett SHORT TERM...Badgett LONG TERM...BSD/Badgett AVIATION...Badgett

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