Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 201844 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 245 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 NIGHT THROUGH FRIDAY/...
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As of 245 PM EDT Friday... ...Unsettled weather for the first half of next week... Upper low over the Deep South Monday morning will begin to gain some latitude Monday night and Tuesday, lifting slowly NNE into the southern Appalachians before eventually becoming absorbed by the kicker shortwave trough diving east/southeast through the central and eastern US. Owing to the slow movement of the upper low across the region, along with early depictions of a very strong Atlantic maritime feed into the area, central NC has the potential to see a widespread soaking of 1 to 2 inches, with localized higher amounts possible, across central NC Monday through Tuesday night. With area rivers and creeks running high from recent heavy rainfall over the past week, this additional rainfall may be enough to result in some localized/minor flooding. Meanwhile, the severe threat at this time,appears to be low with much of the forecast area expected to stay in the cool stable low-level NELY flow, north/northwest of the surface low as it tracks along the coast. If future model runs trend farther inland/westward with the track of the low, there will be a greater convective threat across eastern/southeastern portions of the forecast area. Rain chances should decrease on Wednesday, but the approach of the aforementioned shortwave trough into the eastern US, followed by yet another shortwave trough dropping southeast into the region will support scattered showers through Thursday. Insitu CAD in place east of the mountains, along with widespread rain and extensive cloud cover will hold temperatures down into 60s Monday and Tuesday, with it definitely plausible that highs Tuesday across the the heart of the damming region across the NW Piedmont, could struggle to climb out of 50s. Although rain chances should decrease significantly on Wednesday, without a well-defined mechanism to erode the lingering low-level wedge/low clouds, temperatures could be slow to recover/moderate through the remainder of the work week.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... 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. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...WSS NEAR TERM...WSS SHORT TERM...Badgett LONG TERM...CBL AVIATION...WSS

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