Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220907 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 406 AM EST Wed Nov 22 2017 .SYNOPSIS... A weak area of low pressure off the NC coast this morning will accelerate northeastward off the Mid-Atlantic today. Meanwhile, a cold front will move through the area later this morning. Cool high pressure will build over the area tonight through Friday. && .NEAR TERM /THROUGH TONIGHT/... As of 335 AM Wednesday... Batch of short wave energy currently over the SE/Carolina coast will accelerate NEWD up the Mid-Atlantic Coast today, ahead of the northern stream trough and attendant cold front moving in from the NW. The associated offshore coastal low will follow suite, which means that the back-edge of the shallow convection will exit the coastal plain counties shortly after daybreak. In the interim, as the back-edge of the convection and clouds pushes east, a brief period of dense fog is likely across the western and central Piedmont this morning. Will issue a dense fog advisory as needed. Subsidence in the wake of exiting shortwave disturbance, aided further by post-frontal dry air advection, will allow for abrupt clearing of cloud cover this morning, with NWLY wind gusts into the teens at times during the late morning and into the afternoon. Seasonable highs this afternoon in the upper 50s NW to mid 60s SE. While continued CAA will largely govern min temps tonight, re- intensification of a 80-90 kt upper jet streak across the Carolinas this evening and overnight, owing to the approach of the next batch of southern stream energy lifting NE out of the Gulf of Mexico, will result in a resurgence of high-level moisture/cirrus cloud cover, very likely sufficiently opaque to temper radiational cooling. Lows in the lower to mid 30s. && .SHORT TERM /THURSDAY AND THURSDAY NIGHT/... As of 350 AM Wednesday... WV imagery this morning indicates a shortwave trough in nw flow aloft has amplified strongly across ern TX and into the nwrn GOM during the past 12 hours; and the latest model guidance suggests it will continue to amplify deep into the cntl GOM by 12Z Thu. Meanwhile, a shear vorticity maxima now migrating through swrn Canada, atop a highly amplified wrn conus ridge, will amplify sewd and into the mid MS Valley and mid-South through the same time. The former feature is the one the models had indicated would lift newd and yield a chance of rain across the sern US --including sern NC-- on Thanksgiving Day. Given how deep into the GOM this trough is forecast to plunge, it now stands little to no chance of gaining enough latitude to produce any impacts in cntl NC this period, aside from cirrus/cirrostratus in swly high level flow downstream of the trough. At the surface, a 1032 mb, arctic surface high centered over the upr MS valley this morning will weaken and modify considerably as it migrates ewd to the cntl Appalachians and middle Atlantic states by Thu-Thu night, while low pressure drifts slowly newd through the ern GOM, and renewed coastal frontogenesis occurs downstream of the low/off the sern US coast. Sensible weather resulting from the pattern described above should accordingly be mainly a temperature forecast, impacted very minimally by the aforementioned high level moisture forecast to stream across mainly the ern half of the RAH CWFA - highs in the upr 40s to mid 50s, and lows within a few degrees either side of the freezing mark. && .LONG TERM /FRIDAY THROUGH TUESDAY/...
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As of 400 AM Wednesday... Little change in forecast rationale this period. The large scale pattern is forecast to begin a period of transition from a stable, highly amplified one across the conus, consisting of a persistent mean ridge centered near Baja CA and a longwave trough over the ern US, to a more progressive one that will allow for the ridge to expand ewd across the sern US by the middle of next week. At the surface, high pressure will generally dominate the weather over NC, though with a coastal frontal zone and embedded waves of low pressure passing close enough to threaten perhaps the far srn/ern Coastal Plain with a slight chance of rain Fri-Sat. Otherwise, a reinforcing and moisture-starved, nrn stream cold front will sweep across NC Sat night-Sun, only to usher additional surface ridging overhead for next week. Like the pattern aloft, temperatures will be in a continued state of transition, climbing well into the 60s ahead of the aforementioned dry cold front by Sat, will post-frontal 50s Sun-Mon, then modifying back into the 60s for most by the middle of the week.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... As of 135 AM Wednesday... An area of low pressure will track NE, off the NC coast overnight. Showers will overspread the area through daybreak, with the greatest concentration of showers expected at the eastern terminals. Pockets of IFR/LIFR ceilings may develop for a brief period at KRDU, KFAY and KRWI between 06 to 12z. Meanwhile, at KINT and KGSO, patchy fog could develop between 09 to 12z as cloud cover clears out, reducing the visibility to between 1-3 miles. A cold front will sweep across central NC Wednesday morning, leading to improving aviation conditions as ceilings will quickly lift and dissipate by 15z. Sfc winds will be brisk Wednesday morning through mid afternoon with gusts approaching 20 kts. Expect predominately VFR conditions through Sunday. The exception could be near the far eastern zones Friday and Saturday in association with another coastal low pressure system. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...CBL NEAR TERM...CBL SHORT TERM...MWS LONG TERM...MWS AVIATION...CBL

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