Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 040744
Area Forecast Discussion
National Weather Service Raleigh NC
245 AM EST Sun Dec 4 2016
High pressure will extend into the area from the north this morning.
Low pressure will track from the Gulf Coast across the Southeast
states late today through tonight, before moving off the coast
Monday morning. High pressure will build in briefly from the north
Monday afternoon, then a second stronger low pressure system will
cross the Gulf States and Carolinas Monday night through Tuesday.
.NEAR TERM /today through tonight/...
-- Changed Discussion --As of 245 AM Sunday...
Surface high pressure nosing southward from the central Appalachians
into central NC is capped by a broad mid level ridge axis this
morning, however this will soon give way to deepening moisture as
the axes of both ridges shift eastward and IVT strengthens over the
area, with the arrival of a weak mid level perturbation which
flattens the mean flow over our region. Somewhat deep but weak moist
isentropic upglide is already underway across western NC into the
western/southern Piedmont, topped by weak upper divergence, although
the subcloud layer here remains fairly deep, causing precip to be
light and more patchy. This scenario should persist through much of
this morning as the initial forcing for ascent will be rather weak
with high cloud bases. But models show upglide gradually
strengthening through the 285K-305K depth by early afternoon and
remaining strong and deep over central/eastern NC from mid afternoon
through much of tonight, coinciding with the west-to-east passage of
the 850 mb SSW-erly jetlet across GA and the Carolinas, as well as
with weak low pressure tracking from the Gulf Coast across the
coastal Carolinas. Expect rain chances to increase by midday to
categorical SW ranging to just slight chances NE where the surface
ridge will hang on longer, all in line with consensus of large scale
models as well as recent CAM runs. This will be followed by a trend
to categorical pops over all of central NC by mid-late afternoon,
persisting through midnight. Expect amounts through tonight to range
from around a half inch in the north to around an inch across the
south. This upglide will diminish late tonight as the low level jet
shifts to our east, with the onset of downslope-directed low level
flow and the departure of the weak surface low and weak mid level
wave. Expect pops to trend down to chance NW but stay categorical in
the SE until just before dawn. Below normal thicknesses with clouds
and rain falling into a lingering stable pool favor chilly highs
from the mid 40s NW to lower 50s E. Lows tonight 40-46. -GIH
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.SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/...
As of 340 PM Saturday...
Rain Sunday night will taper to light rain or drizzle late as the
initial surge of lift shifts to our NE and the initial wave of low
pressure is forecast to move NE off the coast by 12Z/Monday. Temps
should hold steady in the 40s/lower 50s NW to SE.
The passage of the wave will bring a break in the rain chances for
most of Monday. This occurs as another (this time weaker) surface
high builds in from the north Monday. Some residual affects of the
CAD should linger Monday in the heart of the Piedmont with plenty of
clouds and some light mist or drizzle. Low clouds early may give way
to breaks in the clouds around the edges of the damming Monday
afternoon. However, we will undercut highs Monday going below
statistical guidance by 5 degrees in the W-N Piedmont (near 50), but
go close to guidance where breaks should occur (Sandhills, Coastal
Plain) may see lower 60s.
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
As of 400 PM Saturday...
The parent storm is still expected to take on a "Miller B" scenario
Monday night and Tuesday. This means the parent storm tracks NE from
the Gulf of Mexico through the Ohio Valley Mon night. As this storm
weakens, another develops along the SC coast (coastal front) and
tracks along the NC coast Tuesday and Tuesday night.
Another hybrid CAD event is expected as surface high pressure is
forecast to become established from NY to western SC in the Miller B
scenario. Lows Monday night generally in the 40s. Highs Tuesday will
hold in the 40s in the Piedmont, with near 60 SE. Some lingering
light rain or drizzle expected Tuesday night with temperatures
holding steady or slowly rising.
Ample moisture from both the Atlantic and Gulf will be pulled into
the system and the result will be rain developing again Monday night
and continuing Tuesday. The back edge or end of the significant rain
should arrive very late Tuesday with models in general agreement on
this timing. QPF this time should be heavier, with 1 to 1.5 inches
The first very cold air mass originating in Alaska and the Yukon
will arrive in the mountains as early as Thursday. Models are
trending faster and are more in line with the GFS (preferred
solution) in pushing this air mass across the mountains to the coast
late Thursday and Friday. Any showers would be rain and prefrontal
in the warm air.
Wednesday will be mild with decreasing clouds and temperatures in
the 60s. Much colder temperatures are expected Thursday through
Saturday with the heart of the cold for our region Friday into next
weekend. Our coldest lows should be 20-25 and highs mid 30s to mid
40s Friday and 40-45 Saturday.
.AVIATION /06Z Sunday through Thursday/...
As of 1245 AM Sunday...
VFR conditions will hold through this morning across Central NC,
although mid and high clouds will continue to overspread the area
from the west. Cigs will stay above 5,000 ft AGL areawide through at
least 17z. But conditions will gradually deteriorate this afternoon
from SW to NE as surface low pressure and an upper level disturbance
track across the Gulf States toward the Southeast. Cigs will drop to
MVFR at INT/GSO starting around 18z with light rain spreading in,
then at RDU/FAY starting around 21z, and at RWI starting around 02z
this evening. Cigs are then expected to drop to IFR at INT/GSO after
21z and at RDU/FAY after 02z this evening. The rain will initially
be light as it first arrives today with VFR vsbys holding, however
as the rain intensity picks up a bit later today, vsbys will drop to
MVFR in the late afternoon (INT/GSO) through evening (RDU/FAY/RWI).
Winds will be light mainly from the NE initially before shifting to
blow from the E and SE late today into tonight, remaining light.
Looking beyond 06z late tonight, high confidence in poor aviation
conditions, primarily IFR/LIFR cigs and MVFR/IFR vsbys, dominating
later tonight through daybreak Mon. Rain will gradually taper off
from NW to SE Monday morning with conditions rebounding to VFR
areawide. VFR conditions will dominate from around 18z Mon until
around 06z Tue. Then another storm system will cause IFR conditions
to return after 06z early Tue morning, lasting through much of Tue
with steady widespread rain returning. Rain will end late Tue,
although IFR clouds will hold into Tue night. Improvement to VFR is
expected Wed, then will drop back to MVFR/IFR Wed night. Cold front
passage may bring VFR conditions once again Thu. -GIH