Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 221437 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 1036 AM EDT THU SEP 22 2016 .SYNOPSIS... Deep low pressure will hold over the eastern Carolinas through Friday. This low will weaken Friday night through Saturday, as a backdoor cold front approaches from the north. && .NEAR TERM /THROUGH TONIGHT/...
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As of 1035 AM Thursday... With little change in the overall pattern, featuring a surface low and associated inverted sfc trough off the Carolina coast and a closed but weakening mid/upper level over the heart of the Carolinas, the damp and unsettled weather will continue for one last day. DCVA in tandem with improving upper divergence, and with ample low level moisture convergence, will likely lead to redevelopment of scattered to numerous showers mainly along and east of Highway 1 this afternoon. While isolated pockets of heavier rain are possible today within the above-normal PW environment, amounts should be notably less overall given the weaker dynamic forcing for ascent and slowly filling mid level low over the eastern Carolinas. Under a veil of overcast low clouds, temperatures again will be held in check, but not to the degree they were yesterday as rain/drizzle this morning is not as widespread. Highs in the mid 70s to around 80. Tonight: With closed low devolving into an open wave trough, decreasing upper level support and shallower saturation through the column will support less in the way of rain/drizzle overnight. Lows 65-69.
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&& .SHORT TERM /Friday through Friday night/... As of 228 AM Thursday... The mid level trough continues to tilt and ease toward the SE Fri/Fri night, due in large part to a potent vortex moving through the Intermountain West and the subsequent downstream height rises through the middle CONUS and mid-lower Miss Valley. The surface low as well continues to fill and shift enough toward the ESE to allow the drying aloft to work down into the boundary layer, resulting in diminishing rain chances and increasing sunshine. Remaining high PW over 1.6" and the last lingering traces of the departing trough over the SE half of the forecast area necessitate leaving a chance of showers and perhaps an isolated storm in this area, while NW sections will be drying out through the column. Low level thicknesses are likely to recover sufficiently (around 10 m above normal) with greater sunshine (mainly NW half) to push Fri highs into the lower-mid 80s. The deeper dry air moves into the area from the NW in full force Fri night, and will taper pops down and out for Fri night with clearing skies. Lows again in the mid-upper 60s. -GIH && .LONG TERM /Saturday through Wednesday/... As of 300 AM Thursday... Extremely low confidence forecast in place as run to run consistency in the models has been non-existent, particularly on the back end of the long term forecast. As far as the weekend forecast, a backdoor cold front is progged to move through late Saturday or early Sunday and bring temperatures down from the mid to upper 80s on Saturday to the upper 70s to low 80s on Sunday. Models and forecast soundings indicate a mostly dry frontal passage at this time. As the forecast moves into the early part of next week, model agreement breaks down considerably with the GFS presenting a blocked flow scenario and the ECMWF not buying it at all as the high to the north behind the cold front is very transitory, migrating from New England, out into the western Atlantic. The ECMWF solution allows a low pressure system centered over the upper plains to move eastward into eastern Canada and drag a cold front with it. This puts the cold front over the Carolinas by Wednesday, whereas with the GFS blocked solution, the same front is not allowed to progress into the Carolinas until Friday. The upshot of all this is that through midweek, the difference in model guidance should not affect the precipitation forecast all that much as most solutions are fairly dry with only slight chances in the forecast, mainly with moist return flow around the high in the western Piedmont. Temperatures may be another story, being much harder to forecast due to the placement of the high with the GFS solution well north, and thus cooler than the further south ECMWF scenario. For now will go with temperatures starting out cool on Wednesday in the mid to upper 70s and moderating into the low to mid 80s by midweek. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... As of 655 AM Thursday... Adverse aviation conditions are likely through at least the morning hours areawide, with IFR conditions expected at sites along/east of highway 1 including RDU/RWI/FAY, and MVFR conditions at western sites including INT/GSO. Areas of light rain will be departing RWI/FAY but will move into RDU/GSO and perhaps INT over the next few hours, prior to daybreak. Cigs will lift to MVFR by 16z-18z, and will likely remain mostly MVFR through most of the afternoon areawide, except at FAY where cigs should rise to VFR after 18z. Periodic light rain is expected to persist at RDU/RWI/FAY late morning through afternoon with occasional MVFR to IFR vsbys. Cigs/vsbys will once again drop to IFR toward the end of the TAF valid period (after 05z). Winds will remain from the northeast today at 6-12 kts with gusts to around 15 mph possible. Looking beyond 12z early Fri morning: IFR/LIFR conditions are expected to hold through daybreak in the west (INT/GSO/RDU) and through mid to late morning in the east (FAY/RWI). As surface low pressure along the Carolina coast weakens and shifts eastward, with lessening influence on central NC, conditions will trend to VFR areawide by 22z with any lingering showers in the east ending. VFR conditions will then dominate through Monday, although early morning fog is possible early Sun morning, and MVFR cigs are possible Sun night through Mon morning as a front drops into the area from the NNE. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...CBL SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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