Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 250621
Area Forecast Discussion
National Weather Service Raleigh NC
220 AM EDT SUN SEP 25 2016
-- Changed Discussion --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.
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.NEAR TERM /OVERNIGHT/...
As of 1045 PM Saturday...
Skies were mostly clear across central NC this evening as a weak
ridge of high pressure aloft extended across the region. A surface
cold front extended from the Tidewater region of VA northwestward
into the central Appalachians. Due to the deep nw flow on the front
side of the upper ridge, the sfc front will only edge slowly
southwest into our region overnight. Thus, mostly clear skies will
reign for most of the night for locations southwest of Raleigh,
likely not becoming cloudy until close to or after daybreak. This
may allow patchy or areas of fog to develop though not anticipating
the need for a dense fog advisory at this time.
Still expect to see a low deck of clouds infiltrate the northeast
counties after midnight with a few sprinkles possible, especially
near the VA border.
Overnight temps should generally range between 65 and 70.
.SHORT TERM /SUNDAY and SUNDAY NIGHT/...
As of 130 PM Saturday...
A quick turn from summer to fall expected Sunday with some hybrid
CAD expected into the Piedmont region Sunday and Sunday night.
Sunday will bring much more fall-like conditions led by the cooling
NE flow and cloud cover. The cooling conditions will be pushed down
the eastern seaboard by surface high pressure (1025 MB) centered
over SE Canada. The high pressure ridge is forecast to extend
southward into NC/SC into Sunday night before the ridge axis moves east.
Models still bring low stratus deep into our region with even a chance of
light drizzle in the NW Piedmont by early Sunday afternoon. It appears
that little if any QPF can be expected as the moist upglide is expected
to be too shallow for anything more that a trace
to 0.01 or 0.02 in the northwest zones, with nothing more than a sprinkle
expected elsewhere. Highs will be much cooler with overcast skies in
much of the region. Highs Sunday will be coolest in the north-central
Piedmont where readings may hold in the 60s. Elsewhere, highs will range
into the 70s across the south and west. The overcast may break into
variably cloudy skies in the SE, otherwise extensive cloudiness is
expected through the day into Sunday night. Lows Sunday night in the upper 50s
to mid 60s.
.LONG TERM /MONDAY THROUGH SATURDAY/...
As of 310 PM Saturday...
Monday through Tuesday night: Surface high pressure is expected to
shift eastward and off the Northeast U.S. coast on Monday, with any
hybrid CAD eroding from SE to NW with possibly some lingering light
precip (mainly west where the damming should linger the longest).
High temps are expected to generally range from the mid to upper 70s
north/northwest to the lower 80s south.
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
.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --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
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