Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 100532
Area Forecast Discussion
National Weather Service Raleigh NC
1233 AM EST Sat Dec 10 2016
-- Changed Discussion --Cold high pressure will build across the area through tonight, then
shift offshore Sunday. A cold front will approach from the west
late Sunday and move through the area on Monday.
-- End Changed Discussion --
.NEAR TERM /THROUGH TONIGHT/...
As of 815 PM Friday...
1040+ mb surface high pressure was centered over the Northern
Plains states this evening. Bitterly cold air was associated with
this high. The high pressure continued to build and extend SE to
encompass much of the central and eastern United States. Even though
the arctic air is greatly modified as it reaches our latitude, the
temperatures were still around 15 degree below normal for mid-
December with the air mass. These numbers seem almost mild if
compared to the temperatures directly under the high pressure over
MT/ND/MN, where readings were 25 to 35 degrees below normal.
Cold air advection continued over our region with the NW flow. The
pressure gradient will continue to weaken overnight as the core of
the high shifts SE toward the mid-Mississippi Valley region. Clear
skies are expected with good to excellent radiational cooling as
winds die off to less than 5 mph. Dew points were already in the
teens and lower 20s. Expect lows to fall to 20-25 except around 18
in the rural Piedmont locations.
.SHORT TERM /Saturday through Sunday night/...
As of 335 PM Friday...
Sat/Sat night: The surface high builds overhead through Sat night,
as the mid level flow becomes more zonal. We should see an increase
in high thin clouds, especially late Sat into Sat night, as weak
perturbations and high level moisture move out of the Front Range
and across the Mid-Atlantic region. Thicknesses will start out a bit
cooler Sat morning than this morning, although this will be
partially offset by some afternoon recovery, which should lead to
highs similar to today, in the 40-45 range. Lows Sat night in the
low-mid 20s, with light to calm surface winds and a veil of high
thin clouds and patchy mid clouds overnight.
Sun/Sun night: The 850 mb anticyclone will shift off the Southeast
coast late Sat night into early Sun morning, inducing low level warm
advection just above the slowly-departing surface high. This warm
advection will strengthen over time Sun/Sun night, and models agree
on increasing and deepening moist isentropic upglide, starting at
285K-290K, focused on the eastern CWA. Expect increasing clouds
roughly from S to N Sun afternoon, trending to mostly cloudy
areawide by sunset, and remaining cloudy Sun night. The column
remains dry above the freezing level through Sun night, so any
precip should be fairly light with pops no better than chance. With
rising thicknesses balancing increasing clouds, expect still-cool
highs in the 43-50 range. After a slight dip in temps Sun evening,
readings should hold steady or rise a bit overnight. Lows 39-46. -GIH
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 210 PM Friday...
Initial low amplitude long wave troffing will produce fast and near-
zonal flow across the central and southern tiers of the Conus
through mid week. Return flow ahead of an initial front on Monday
will produce a strong surge of warm air advection with highs ranging
from upper 50s across the north to mid 60s in the south...5 to 10
degrees above normal. Moisture advection will cut off pretty quickly
as low level flow turns westerly across the Gulf states...with
chance PoPs during the day shifting to the east and diminishing
post-fropa on Monday night.
The frontal zone aligns parallel to the flow and forecast details
are murkier heading towards midweek with considerable variability in
model solutions. The frontal zone looks to remain south of the
area...with small chance PoPs mainly across the southern tier...
both Tue and Wed as surface high pressure races across the Ohio
Valley. Highs will be on a gradual fall as the upper trof amplifies
a bit and we should be in a predominantly cloudy regime. Highs
Tuesday in the mid to upper 50s will fall to the low and mid 50s on
Confidence in model solutions for the late week is even lower
although colder air will continue edging southward. The upper flow
is not highly amplified, however, which will block off the really
frigid airmass north of the area. Regardless, highs will probably
top out in the mid 40s after morning lows in the mid to upper
20s both Thu and Fri.
.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --As of 1230 AM Saturday...
High confidence that VFR parameters will persist across central NC
through 12Z Sunday as high pressure at the surface will be the
dominate weather player. Westerly flow aloft will advect high level
moisture across the area later today an tonight in the form of
The high will shift offshore Sunday. the return flow on the backside
of the retreating high will advect low level moisture into central
NC late Sunday and Sunday night, resulting in MVFR, and eventually
IFR ceilings. In addition, patches of light rain should develop
Sunday night. An increasing low level jet may produce marginal low
level wind shear parameters Sunday night, mainly in the form of
speed shear rather than directional shear, as wind speed 35-40kts
probable between 1500-2000ft.
Variable aviation conditions expected Monday through Wednesday as a
series of low pressure systems cross the southeast U.S. This will
result in periods of MVFR or IFR parameters due to adverse ceilings.
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