Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 100740
Area Forecast Discussion
National Weather Service Raleigh NC
240 AM EST Sat Dec 10 2016
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.
.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 SATURDAY/...
-- Changed Discussion --As of 240 AM SATURDAY...
The general upper level patter in the GFS and ECMWF are very
similar, however there are continued differences between the two
with respect to precipitation chances and timing.
Monday to Wednesday: Monday, an upper level shortwave will traverse
the Great Lakes while the associated cold front will approach
central NC from the north or northwest. Southwest flow ahead of the
front will result in warm advection into the area during the day.
The result will be fairly mild/above normal highs in the mid 50s NW
to mid 60s SE. The front is expected to get hung up in the vicinity
of the NC/VA border Monday Night through Tuesday Night as the parent
surface low moves away to the northeast. Meanwhile, a strengthening
low aloft will move eastward through Central Canada, while the flow
over the Eastern U.S. will become more zonal but slightly troughed.
This will contribute to the stalled southward progression of the
front. There is still a bit of uncertainty regarding the southward
progression of the front and thus the temperatures, particularly
across the north, during this time. As a result, confidence in
temperatures is below average. Will hold off on moving the front
through until late Wednesday or Wednesday night, which will result
in gradually lowering highs in the mid 50s to around 60 degrees
Tuesday to low to mid 50s Wednesday. Lows Monday and Tuesday nights
will be similar, upper 30s north to mid 40s south.
Wednesday Night through Saturday: As the aforementioned upper low
strengthens and slides further to the east-southeast, over Southeast
Canada by Wednesday Night, the trough over the Eastern U.S. will
become more amplified. The cold front will finally push through
Central NC Wednesday Night and subsequent high pressure will move
through the OH valley and into New England through Friday and ridge
southward into NC. Latest model runs indicate strong CAD setting up
for Friday Night into Saturday. The problem comes Friday night as
moisture advecting into the region in southwest flow aloft may
result in some p-type issues. For now will keep precipitation
chances just below slight until there is a bit more model
consistency and agreement, however wintry precipitation is not out
of the question at the end of the period. Temperatures through the
extended will be below normal with highs in the low to mid 40s
Thursday and Friday, potentially dropping into the mid 30s to low
40s for Saturday. Lows will generally be in the mid 20s to low 30s.
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.AVIATION /06Z SATURDAY THROUGH WEDNESDAY/...
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.