Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 240038 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 838 PM EDT FRI SEP 23 2016 .SYNOPSIS... An upper level low and the remnant low from Julia will linger and weaken near the southern Carolina coast through Saturday. A cold front will drop south into the area late Saturday and stall south of the region on Sunday. A stronger cold front will push through the region late Tuesday or early Wednesday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... As of 325 PM Friday... 18 UTC surface analysis shows the persistent remnant low from Julia becoming elongated and located off the northeast SC coast. A weakening mid level vortex that was located across the eastern Carolinas was beginning to shear out and open up as a well defined shear axis drops into NC. The air mass across the eastern Carolinas remains very moist with precipitable water values in excess of 1.9 inches in the southern coastal region and Coastal Plain with much drier air, noted by PW values of 1.5 inches or less moving into northern and northwestern NC. The latest visible satellite imagery shows clearing skies moving into northern and northwestern NC with the widespread stratus across southeaster NC giving way to an increasing amount of breaks in the overcast. Widely scattered showers have developed to the south and southeast of Rocky Mount, Raleigh and Troy with more numerous showers and thunderstorms along the immediate NC coast. Convection allowing models fit current trends well and gradually push the scattered showers in central south this afternoon before dissipating early this evening. While the latest analysis shows the air mass weakly unstable with MLCAPE values between 500 and 1000 J/Kg, we have omitted the inclusion of thunder in the forecast. Skies should continue to clear this evening with the loss of heating and the arrival of drier air and subsidence behind the shear axis. Some clouds may persist across the southeast before areas of fog and perhaps some low stratus develop overnight. The stratus will be most widespread from the northern Coastal Plain southwest across the remainder of the Coastal Plain into the Sandhills and eastern Piedmont. Lows tonight will range in the mid 60s northwest to near 70 southeast. -Blaes && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... As of 320 PM Friday... Fair weather and warmer temperatures are expected on Saturday as weak high pressure is present across the region at the surface and ridging to the west extends into the area. The air mass dries out considerably from previous days with precipitable water values during the day ranging less than 1.25 inches across most of central NC. With a good deal of sunshine and an increase in low level thickness values, have adjusted maxes for Saturday upward a couple of degrees. Both the NAM and GFS MOS gives a high of 88 for RDU but the most recent EC MOS provides a high of 91. If we get a good amount of sunshine as expected, highs should easily range in the upper 80s to around 90, perhaps a couple of degrees warmer. A cold front will drop south across the Mid Atlantic Saturday morning and move into NC during the late afternoon or evening and then push toward the SC border on Saturday night. NWP guidance has trended wetter with this system. There may be some light precipitation generated behind the front overnight that pushes south across the northeast Piedmont and northern Coastal Plain. The boundary layer is initially rather dry but it moistens overnight with some low stratus and drizzle possible by morning. Overnight lows should range in the mid to upper 60s. -Blaes && .LONG TERM /SUNDAY THROUGH FRIDAY/... As of 245 PM Friday... The timing of the back-door cold front through the area on Sunday is still in question. The GFS and NAM are much quicker to blow the front south through the area late Saturday night/ear Sunday, while the ECMWF suggest the frontal boundary will tend to "hang up" or slow down across the forecast area on Sunday, which is very plausible given weak sfc pressure rises from the transitory parent high center retreating off the Northeast-Southern New England Coast. These models discrepancies are leading to lower than average forecaster confidence, making for a challenging temperature forecast on Sunday and likely setup a sharp temperature gradient across the area. For now will continue a "middle of the road approach" with highs ranging from mid 70s northeast to mid 80s southwest. Additionally, given the potential for the front invof the area, will continue isolated to slight chance chance pops. Mid/upper level ridge will build east over the area on Monday in advance of a closed low and upper trough progressing eastward into the Upper Great Lakes/Southern Canada. With the transitory parent high quickly moving off the Southern New England Coast, south- southeasterly return flow will quickly return to the area late Monday with rain chances generally restricted to upslope/differential heating over the higher terrain, while ridging aloft should keep the remainder of NC dry. SELY moisture advection and resultant weak isentropic upglide in advance of a cold front approaching from the west could produce showers across the area as early as Monday night/Tuesday morning with another round of showers and storms expected to accompany the frontal passage Tuesday afternoon/evening. Highs Monday and Tuesday slightly above normal with mild overnight lows in the 60s. In the wake of the cold front, high pressure will bring dry seasonable weather for the later half of the work week. Highs 75-80. Lows the 50s. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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As of 835 PM Friday... 24 Hour TAF Period: VFR conditions are expected to continue this evening, with any isolated showers from early today having dissipated with the loss of daytime heating. While the weak area of low pressure has moved further to the south and east of the area this evening and skies have generally cleared, we still expected some sub-VFR conditions to develop overnight. Given mostly clear skies and calm to light and variable winds overnight, coupled with recent rainfall, expect we will see some sub-VFR visbys develop after midnight through around sunrise. Conditions are expected to range from VFR/possibly MVFR at KGSO/KINT to IFR/LIFR at KRDU/KFAY/KRWI. Any reduced visbys that develop should lift and scatter within a couple hours of sunrise. VFR conditions are expected to continue after the morning fog lifts/dissipates, with generally light wind with a northerly component. Outlook: VFR conditions are expected on Saturday evening before a cold front moves into the region from the north Saturday night. A period of adverse aviation conditions including reduced ceilings and visibilities in showers are possible beginning late Saturday night/Sunday morning and continuing through early Monday. Another period of adverse aviation conditions is possible late Monday into Tuesday as another cold front approaches the region.
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&& .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...BLAES NEAR TERM...BLAES SHORT TERM...BLAES LONG TERM...CBL AVIATION...BSD/BLAES

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