Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250710 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 310 AM EDT SUN SEP 25 2016 .SYNOPSIS... A backdoor cold front will move southwestward through the area today, as a cooler air mass pushes in from the north. This front will weaken and move back northeastward as a warm front on Monday. Another cold front will approach from the west Monday night, and then slowly cross the region Tuesday through Tuesday night. && .NEAR TERM /today and tonight/... As of 250 AM Sunday... The backdoor front has pushed to the SSW through the northeast third of the CWA thus far, and will continue this progression through today, albeit with a slowing trend. This will mean mostly cloudy skies for all but the far western and southern sections as post- frontal stratus spreads in, although this is likely to break up this afternoon, allowing peeks of sunshine. In the SW CWA, models suggest that the cooler and more stable low level air may be sufficiently delayed this afternoon to allow for marginal elevated destabilization there, so have added isolated thunder in this area this afternoon into early evening. Low level thicknesses will be near or just above normal to start the day, however with minimal recovery today and the expansiveness of low clouds through much of the day, expect highs from the mid 70s near the VA border to the mid 80s in the far SW. Stable low levels persist tonight, with some lingering moisture beneath the relative warm layer aloft (between 850 and 700 mb) that should be stubborn to dislodge especially in the western CWA where moist upglide will hold. Expect partly cloudy skies tonight east (much weaker to absent moist upglide and slightly drier low levels) and mostly cloudy to cloudy west with patchy light rain or drizzle possible. Lows from around 60 near the VA border to upper 60s SW. -GIH && .SHORT TERM /Monday through Monday night/... As of 305 AM Sunday... The work week will start with the cool surface ridge centered over SE Canada nosing south/southwestward through the NC Piedmont, capped by mid level shortwave ridging between deep shortwave troughing over the upper Midwest and off the Canadian Maritimes. The remaining low level stable pool will hold firm for the first half of the day, then slowly erode throughout the afternoon as the parent high eases eastward and weakens, with fairly dry mid levels allowing for some wedge-dissolving isolation. This dry air will be quickly supplanted however as moisture ramps up and deepens by late in the day, as the mid level trough axis and surface cold front approach from the WNW. Jetting on the east side of the upper level trough will result in improving upper divergence across western/central VA/NC late Mon into Mon night, with rebounding prefrontal PW to over 1.75". Will hold onto slight chance pops east (longer-lasting dry air) and better chances east, trending upward slightly through the late day and night as large scale forcing for ascent ramps up. Expect highs Mon from the upper 70s to lower 80s, followed by lows in the mid- upper 60s Mon night. -GIH && .LONG TERM /Tuesday through Saturday/...
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As of 310 AM Sunday... A cold front will make its way through the state on Tuesday as the parent low pressure system becomes stacked over the Great Lakes. At this point it looks like there will be hardly any punch at all with this system and thus expect most of the precipitation to be in the form of convective showers with isolated thunder possible Tuesday afternoon, particularly across the south but otherwise instability is lacking. The effects on temperature will not be seen until Wednesday and beyond so expect highs on Tuesday near 80 degrees with upper 70s across the north. The real curiosities in the long term center around how the stacked low will evolve over time. The GFS solution has the low remaining embedded in the upper level flow and gradually moves eastward keeping the end of the week dry. The ecmwf solution is much different and is beginning to gain a little consistency with the upper low cutting off from the mean flow and dropping south along the Appalachians and hovering there for several days. This would greatly increase precipitation chances over our area for the end of the week and needs to be watched because the latest run of the GFS is showing a bit of a trend toward that upper low dropping further south although it has not cut it off yet. For now will keep the forecast dry outside of slight chances for showers across the east on Thursday but if this trend in the forecast continues, then pops will need to be increased significantly for the end of the week. Temperatures will drop back into the mid 70s for highs for the rest of the week with lows in the middle 50s.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/... As of 220 AM Sunday... RDU/RWI have already seen a trend toward IFR or low-end MVFR cigs as stratus pours in behind a backdoor cold front pushing toward the SSW through NC this morning. This low-end MVFR or IFR stratus will continue moving through the remainder of central NC through daybreak, with winds shifting to light (under 8 kts) from the NE or ENE. A period of MVFR vsbys is also possible this morning through 13z. Cigs will slowly lift to MVFR areawide by midday, with lowest cigs holding at INT/GSO, then to VFR at RWI/RDU/FAY by 19z while MVFR cigs hold at INT/GSO, through the end of the TAF valid period. A few light showers or sprinkles are possible at all sites today, with little to no risk of thunder. Looking beyond 06z early Mon morning, MVFR conditions will hold at INT/GSO with VFR cigs elsewhere through Mon morning, followed by VFR conditions areawide Mon afternoon/evening. IFR conditions are expected to develop late Mon night, trending to MVFR Tue morning with improving rain chances, as a cold front approaches slowly from the west. A period of sub-VFR conditions is likely late Tue into Wed as the front moves through with scattered to numerous showers and a few storms. Conditions will improve to VFR from west to east Wed night, lasting through Thu behind the front. -GIH && .RAH WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Hartfield NEAR TERM...Hartfield SHORT TERM...Hartfield LONG TERM...Ellis AVIATION...Hartfield

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