Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 220759 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 359 AM EDT Sun Oct 22 2017 .SYNOPSIS... High pressure will extend across the eastern United States through tonight. Meanwhile, a strong frontal system will approach from the west and cross the Appalachians and Carolinas late Mon through early Tue. && .NEAR TERM /THROUGH TONIGHT/... As of 350 AM Sunday... A strong mid to upper level ridge (323 dm @ 700 mb and 593 dm @ 700 mb) analyzed along the coast of the Carolinas will drift only slowly ewd through tonight, downstream of a potent shortwave trough forecast to become a closed low as it migrates from the TX panhandle ewd to the Mid-South. At the surface, 1029 mb high pressure just offshore the middle Atlantic coast will continue to extend swwd into the Carolinas. Persistence will still largely prevail for today, although another day`s worth of ely low level flow around the ridge will allow surface dewpoints to climb more solidly into the 50s, to around 60 degrees or so in the Sandhills and srn Coastal Plain, by this evening. This will favor both slightly higher RH values than recent days, and also (mostly) few-scattered stratocumulus midday onward. Indeed, satellite data and surface observations indicate some of this stratocumulus has already moved inland across ern SC and sern NC in the past several hours. Bufr forecast soundings continue to indicate this stratocumulus may become broken in coverage/mostly cloudy by late afternoon-evening over srn and wrn portions of the RAH forecast area. The stratocumulus, and cirrus similar to Sat, are not expected to be thick and widespread enough to impact high temperatures, which should be nearly identical to those of Sat - mid to upper 70s, to lower 80s across the srn Piedmont; Sandhills; and srn-cntl Coastal Plain. Cloud cover will further increase, into the mostly cloudy range particularly west of US Hwy 1, overnight. There too, a few showers may result late, owing to a lifting and erosion of the preceding capping inversion, and saturation in the lowest 10 k ft, as stronger height falls aloft (20-40 m) spread east of the Appalachians. Milder, with lows in the middle 50s to lower 60s. && .SHORT TERM /MONDAY AND MONDAY NIGHT/... As of 330 AM Sunday... A vigorous cutoff shortwave will lift northeast up the Applachians into the mid Atlantic as it is reabsorbed into a longwave trof digging southeast across the Great Lakes. Low level flow will be increasing and providing a strong moisture feed into the southern mountains early Monday, with low level jetting increasing to exceed 50 knots as the flow veers increasingly southerly and begins marching east ahead of an associated surface cold front. While instablity will be limited by cloudiness and numerous prefrontal showers, low level convergence in the frontal zone will be very strong and a line of vigorous convection is expected in the west during the afternoon, which will move east to reach the Coastal Plain after midnight Monday night. The strong low level flow could be translated to the surface by convective activity, so damaging winds will be possible, especially in the convective line accompanying the front. In addition, the low level shear profile would support rotation in stronger storms, so isolated tornadoes cannot be ruled out. Highs Monday will be mild despite cloudiness and shower activity due to strong warm air advection, reaching mostly mid and upper 70s with some lower 70s in the far western Piedmont. Mixing and warm southerly flow overnight will maintain mild mins in the mid 50s northwest to lower 60s east. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 233 AM Sunday... Low level jetting will be moving east of the Coastal Plain early on Tuesday morning, with drier and cooler air beginning to filter in as the moisture tap is cut off. Cloudiness will be diminishing, but low level cold air advection will be delayed until later in the day as the lagging surface front crosses the area. Highs will have time to reach mostly low 70s with some upper 60s in the northwest where cold air advection will begin earlier and there will be additional potential for stratocumulus accompanying the cool surge. With the cool air settling into place, mins Tuesday night will fall to the mid and upper 40s. An additional reinforcing surge of cool air is expected Wednesday as strong shortwave energy digs into the midwest trof, shifting it across the Ohio Valley, with the axis moving across the south Atlantic coast Wednesday night. Highs Wednesday and Thursday will be mostly in the low and mid 60s, with morning mins Thursday morning in the upper 30s to lower 40s. Shortwave ridging and return flow as associated surface high pressure moves offshore will give us a warmup late in the week, with highs Friday and Saturday mostly in the mid 60s to lower 70s. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 220 AM Sunday... Under the continued influence of high pressure along the middle Atlantic coast, generally VFR conditions are expected to persist, aside from another round of radiation fog at RWI this morning. Increasing amounts of low level moisture in ely flow around the surface high will favor the development of stratocumulus, with bases around 4 k ft, which will become increasingly prevalent this afternoon through early tonight, particularly from FAY to GSO/INT. Outlook: Increasingly moist east to sely low level flow off the Atlantic ocean will favor the development of IFR-MVFR ceilings, and perhaps some visibility restrictions at ern TAF sites, late tonight- early Mon. An approaching frontal system will then result in the ewd progression of a band of IFR-MVFR ceilings, showers and isolated storms (some possibly severe), and strong/veering winds with height late Mon and Mon night. && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...MWS NEAR TERM...MWS SHORT TERM...mlm LONG TERM...mlm AVIATION...MWS is the U.S. government's official web portal to all federal, state and local government web resources and services.