Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 141157
Area Forecast Discussion
National Weather Service Raleigh NC
655 AM EST Sat Jan 14 2017
Cool high pressure will briefly build in from the northeast today,
followed by a secondary cold front on Sunday, and then another
reinforcing high pressure Sunday night.
.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --As of 350 AM Saturday...
A cold front has settled south of the SC border this morning, as
a 1042mb surface high noses in from Upstate NY. Areas of light
rain have been steadily moving east along the NC/VA border area
in response to weak 850mb warm advection neat the right entrance
region of the upper jet over the Mid-Atlantic states. Rap
soundings suggest moisture is confined to a layer between 3k and
7k ft and ceilings have been slow to lower. The low-level flow is
still expected to veer to southerly, which should expand the
stratus and southern extent of the light rain, though the rain
will still remain patchy is nature and mainly north of Hwy 64
through early morning. The main impact will be the development of
a cold air damming airmass over the Piedmont and complicate the
high temp forecast.
Precip will move off to the east by midday as the low- level flow
continues to veer around to west- southwesterly and isentropic
lift is rendered essentially neutral. Low clouds will have more
impact across the north and this still supports highs in the
mid/upper 40s, while the expected low clouds across the south will
be thinner and more likely to mix out. Highs int he south have
been nudged a few degrees to reflect a reasonable warmer trend in
Models continue to indicate some drying in westerly flow just
above the surface tonight. This may not be enough to erode all of
the low clouds withing the extend damming region, but it may help
to create some patchy fog. Lows 43-49.
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.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
AS OF 350 AM Saturday...
Sunday looks fairly similar to Friday, with a cold front draped
across VA Sunday morning ahead of an arctic high poised to
build in through Sunday night. If the pattern is similar, then
the front may be a little slower than models project in reaching
central NC, which would then support highs on the warmer side of
guidance for the southern 2/3 of the area (albeit a different
airmass than yesterday). With flat flow aloft and no discernible
forcing for ascent, Sunday should be dry until the front gets
through the area and winds again veer to southerly and maximize
weak isentropic lift over the western piedmont Sunday night. Highs
Sunday 50 to 62 northeast to southwest. Lows Sunday night in the
upper 30s to mid 40s and the cold air damming is reinforced by the
high to our north.
.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 400 AM Saturday...
The models are in relatively good agreement with the progression of
a closed upper low now just west of the Baja of CA, NEwd into OK/KS
by 12Z Mon. Some interaction and phasing of this opening/lifting
trough with one in the nrn stream will contribute to a deepening
surface cyclone forecast to track through the Upper Midwest and
Great Lakes early next week. Meanwhile, the center of 1035 mb high
pressure initially over the Middle Atlantic states on Mon, with
associated hybrid CAD driven by strongly veering flow /WAA centered
in the 925-850 mb layer/ will move offshore by Mon night, but with a
lingering in-situ ridge axis extending over the Carolinas through
early Tue. It will consequently remain cloudy and cool, with a small
diurnal temperature range, and with a chance of drizzle or light
rain, through early Tue.
A warming SSW low level flow will develop later Tue, and continue
until the cold front accompanying the aforementioned cyclone settles
into the Srn Middle Atlantic states with the best chance of
precipitation during the forecast period, late Wed- Wed night.
A kicker shortwave trough now over the NE Pacific will amplify down
the West Coast, then turn ENEwd across the Deep South and TN Valley,
on the nrn rim of subtropical high pressure that will linger near
FL, through the end of the week. SWly flow aloft, and the approach
of an accompanying frontal system, will result in continued mild
conditions through the end of the week, and with a renewed chance of
rain by Fri.
.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --AS OF 655 AM Saturday...
Overall forecast confidence is pretty low. Models have been much
too aggressive or pessimistic with the potential for sub-VFR cigs so
far this morning, even despite some light showers moving just north
of RDU and RWI. However, there is still decent confidence at MVFR
cigs will develop as the low-level flow is just now turning to
southerly, which is what will really aid in the development. In
fact, some MVFR cigs are just now beginning to show near FAY, so the
current TAF will reflect an increase in the chance of MVFR through
late morning, with MVFR more likely to persist at INT/GSO/RDU.
Northeast winds will be mostly light and variable by this afternoon.
Winds just above the surface will swing around to westerly tonight,
which will erode some of the low-level moisture over the area, but
may in turn promote the chance of patchy fog given light wind.
Confidence in less than MVFR or IFR is still relatively low.
Outlook: MVFR or IFR conditions may redevelop late Sunday as another
cold front pushes in from the north and reinforces a cold air
damming airmass over central NC. VFR conditions should return on
Tuesday, ahead of a cold front approaching the region for midweek.
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