Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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596 FXUS62 KRAH 191734 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 135 PM EDT Thu Oct 19 2017 .SYNOPSIS... Surface high pressure over the Mid-atlantic will extend across the region into the weekend. A cold front will approach the area from the west early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1005 AM Thursday... High pressure positioned immediately south of central NC will provided another afternoon with sunny skies and mild temperatures. 12Z upper air analysis depicts the 850 and 700mb ridge axes west-to- east across the the Deep South into South Carolina. This will result in a westerly flow in the lower half of the atmosphere. Aloft, a minor s/w trough will progress sewd across the region. Weak subsidence in the wake of this system will aid in some compressional warming aloft. This warming aloft in conjunction with the modest downslope component of the lower levels winds and warm air advection from the TN Valley should boost temperatures well into the 70s across central NC this afternoon. 12Z GSO sounding suggest a max temp of 77 degrees. This seems a bit too high but will adjust forecast max temp up a couple of degrees from previous forecast, with highs expected to range from the mid 70s NW to the upper 70s SE. Tonight, sfc high pressure will remain in our vicinity maintaining a dry air mass and light/near calm winds. This suggest another evening when temperatures will drop off quickly after sunset, dropping through the 50s. The modifying air mass should result, however, in minimum temperatures generally in the mid-upper 40s. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... As of 235 AM Thursday... Mid level ridge axis will build overhead on Friday into Friday night, resulting in little change in the weather across central NC, other than temps will be a bit warmer. Expect high temps will generally be in upper 70s to around 80. Lows temps are expected to range from the mid 40s in the cold spots to the lower 50s in the urban areas and SE. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... As of 315 AM Thursday... Little change in forecast rationale described well by the previous shift. Mid-upper ridging now over the wrn GOM is forecast to amplify as it builds east, across and offshore the sern US coast through the weekend, and downstream of a powerful trough forecast to amplify across the Rockies and Plains states. The models continue to indicate that this initially meridional trough will separate and yield a closing off of the srn portion of the trough, as an increasingly active srn stream jet in split flow aloft noses across the lower MS Valley by Sun night. Model spread increases with respect to the geometry and progression of a new trough forecast to amplify from the ne Pacific to the Great Lakes vicinity by the middle of next week, and consequently how quickly this trough may serve as a "kicker" to cause the aforementioned lead srn stream wave to lift and accelerate through the Appalachians Mon-Tue. At the surface, high pressure centered over the middle Atlantic states Sat will strengthen, beneath the building ridge aloft, and move off the nrn middle Atlantic and Northeast coast by Sun. A warm front will retreat nwd, in return flow around the high, across the Carolinas Sun-Sun night. This will occur ahead of a deepening surface cyclone and accompanying lead cold front related to the aforementioned srn stream closed low, forecast to migrate ne through the srn and central Appalachians late Mon-Tue. A secondary cold front, one related to the trailing trough forecast to reach the Great Lakes vicinity by the middle of next week, will likely sweep east of the Appalachians and across NC late Tue-Tue night. Sensible weather resulting from the pattern outlined above will include mild and dry conditions this weekend, followed by the passage of a band or bands of showers, and probable QLCS thunderstorms, Mon night-early Tue. Strong and coupled QG and mesoscale forcing for ascent, and strengthening lower and deep- tropospheric flow, will support an associated risk of severe storms over the Carolinas during that time. Much cooler conditions, and variably cloudy ones, with a chance of "instability" showers in cold, cyclonic flow aloft, will follow for Tue night-Wed. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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As of 135 PM Thursday... There is a high probability of VFR conditions to persist across central NC through 00Z Saturday as high pressure at the surface and aloft controls the weather across central NC. The sfc high will drift offshore Saturday. The return low level flow Saturday night will moisten the low level air mass, leading to the potential for patchy fog with MVFR/IFR visibilities, primarily between 09Z-13Z Sunday. The approach and passage of a cold front Sunday night through Tuesday will enhance the probability of sub VFR parameters, primarily lower ceilings. The probability for scattered convection will also increase late Monday into Tuesday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...WSS SHORT TERM...BSD LONG TERM...MWS AVIATION...WSS

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