Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 250705
Area Forecast Discussion
National Weather Service Raleigh NC
305 AM EDT SUN SEP 25 2016
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/...
-- Changed Discussion --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/...
-- Changed Discussion --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
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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