Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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570 FXUS62 KRAH 201719 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 120 PM EDT Fri Apr 20 2018 .SYNOPSIS... Cool high pressure will extend across southern Virginia and the Carolinas through Saturday, then drift offshore Saturday night. An area of low pressure will approach from the west Sunday, and affect our region early next week. && .NEAR TERM /THROUGH TONIGHT/... As of 1030 AM Friday... Main adjustment to the near term forecast was to adjusted hourly temperatures this morning upward 3-4 degrees based on observed trends. 12Z upper air analysis reveals a mid/upper level trough exiting the Carolinas emanating from a closed deep upper low over the Canadian maritime. Behind the trough, a relatively narrow low-mid level ridge extended south-north over the MS Valley. Subsidence in the wake of the trough will maintain clear-mostly clear skies across central NC through this afternoon. Low level cold air advection still occurring per 925/850mb analysis though this is projected to abate this afternoon as the low level thermal trough lifts newd as the ridge shifts eastward. Per 12Z GSO sounding, appears that we should mix up to 850mb where the based on the subsidence inversion commences. Using the dry adiabatic technique, this yields max temps this afternoon in the mid 60s across a large portion of central NC. Tonight, sfc winds should decouple early/by sunset as the sfc ridge extends overhead. The cool, dry air mass in place will permit temperatures to tumble through the 50s into the 40s by late evening, and into the 35-40 degree range by early Saturday. Appears likely that the outlying areas will see overnight temperatures in the mid 30s, promoting the formation of light patchy frost. Will await the 12Z model temperature guidance, then decide if/where a frost advisory needed tonight. && .SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/... As of 245 AM Friday... The chilly high pressure center is forecast to drift off the VA/NC coast late Saturday with another reinforcing high expected to follow Saturday night. Expect only a few jet related cirrus at times, mainly Saturday night. Highs Saturday with light winds should be in the 65-70 range. Lows Saturday night creep up just a bit into the upper 30s to mid 40s. && .LONG TERM /SUNDAY THROUGH THURSDAY/... As of 355 AM Friday... Surface high pressure will extend into the area from the north and northeast on Sunday, with dry weather expected as weak s/w ridging holds over the area. Temps will continue to run below normal on Sunday, with highs generally in the upper 60s/near 70. Meanwhile, a mid/upper level area of low pressure will approach the region from the west over the weekend and move into the TN Valley and Southeast U.S. by early next week, helping to spread precip into central NC by early next week, with a damming air mass developing. This will lead to below normal high temps in the 50s and 60s on Monday and Tuesday, with lows in the 40s and 50s. The latest GFS and ECMWF have trended more inland with an associated surface low tracking across the region on Tuesday evening/Tuesday night, possibly resulting in a chance for some thunderstorms. The initial surface low will lift to the north of the area on Wednesday as the lead s/w trough pivots through the area. However, additional energy is forecast to approach/move through the area on Wednesday night in Thursday, Thus, will maintain a slight chance of showers in the forecast for Wednesday night into Thursday. High temps mid week are expected to recover some, with highs in the upper 60s to 70s, with lows in the 50s && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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As of 120 PM Friday... There is high confidence that VFR conditions will occur across central NC through Sunday afternoon. Sfc winds will gradually veer through the period from north northeast this afternoon, easterly Saturday afternoon, to southeast by Sunday afternoon. Wind speeds will be less than 9kts through Sunday morning, with a slight uptick by Sunday afternoon across the southern counties to around 1 0kts and gusts 15-16kts. An approaching low pressure system early next week will increase the threat for sub VFR ceilings and MVFR/IFR visibilities due to rain and/or fog persist across central NC. The threat for adverse aviation conditions appears greatest from late Monday through Wednesday.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...Badgett LONG TERM...BSD AVIATION...WSS

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