Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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000 FXUS62 KRAH 250705 AFDRAH Area Forecast Discussion National Weather Service Raleigh NC 305 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/...
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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
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&& .LONG TERM /Tuesday through Saturday/...
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As of 310 PM Saturday... Tuesday through Tuesday night: A mid/upper level low will slowly wobble east and southward across the Great Lakes region early next week, allowing an associated cold front to to approach the area on Monday night into early Tuesday, then slowly cross the area on Tuesday into Tuesday evening as the cold front begins to become more parallel to the mid level flow (helping to slow its progress). With regard to any severe threat instability looks to be weak, however, deep layer shear is expected to be respectable. Thus, we could see a some storms even some weakly organization convection, but the severe potential will remain quite low. Highs Tuesday are generally expected to be in the upper 70s to lower 80s, with lows Tuesday morning in the mid to upper 60s and lows Wednesday morning ranging from the mid to upper 50s nw to the lower to mid 60s se. Wednesday through Saturday: the mid to upper level flow pattern is in question mid to late next week, with regard to what happens to aforementioned deep mid/upper low over the Great Lakes early next week. The latest GFS continue to show the feature becoming a deep trough and moving through the area Wednesday/Wednesday night, helping to push the front (which is expected to linger across coastal portions of NC on Wednesday) offshore and away from the area. Meanwhile, this is the second run in a row of the ECMWF showing the mid/upper low sinking southward towards our area mid week, and lingering the low as it becomes cut off from the westerlies. The 00Z ECMWF ensemble members didn`t show much support for the scenario, so will keep the forecast dry from Wednesday evening onward (but will need to watch this). Otherwise, surface high pressure is expected to build/extend into the area through the period, with highs and lows expected to be near to slightly below normal.
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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...BSD AVIATION...Hartfield

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