Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 151920

Area Forecast Discussion
National Weather Service Raleigh NC
220 PM EST Sun Jan 15 2017

A cold front will drop southward and exit the southern counties by
early this evening. High pressure will build in behind the front and
reinforce a cold air damming airmass over the area through Monday


As of 1035 AM Sunday...

Little change in our sensible weather this afternoon. Early morning
upper air analysis depicts a deep wly flow over the region with weak
caa noted at 850mb. Moisture is mainly confined to the lowest 10k ft
of the atmosphere, with the lowest 5k ft rather damp. Variably
cloudy skies will persist with periods of partial sun more likely
across the Sandhills and southern Piedmont compared to the rest of
the forecast area. A surface cold front poised to enter our northern
coastal plain counties late this morning will drift south-southwest
this afternoon. Low level cold air advection behind this boundary
fairly weak. Still, should see a wide range in high temperatures
this afternoon across central NC,varying from around 50 in the far
northeast, to the lower 60s across the southwest. If sun is more
prevalent this afternoon across the south, high temperatures may end
up being 3-4 degrees warmer than forecast.

Tonight: The cold front will push south of the area by this
evening, with weak cold advection and a light northeast wind
overnight. The H9 flow will swing around to southerly after
midnight, resulting weak (and shallow) isentropic lift in the
western Piedmont. As a result, some patchy light rain or drizzle
should break out and drift east through the Piedmont through
Monday morning, with low clouds eventually engulfing the entire
area. Lows 38-45. ~SMITH


As of 350 AM Sunday...

CAD will persist Monday as the parent surface high shifts to the
Mid-Atlantic coast and then eventually offshore. The main impacts
look to be from just widespread low clouds since the H9-H85 flow
is weak (< 30kt) and the flow aloft is flat. Low clouds will
result in highs several degrees cooler than today, but the lack of
precip should keep highs within a couple degrees but on the cooler
side of guidance; 45-52. The aforementioned surface high will
shift offshore Monday night, but our CAD airmass should linger
without an erosion mechanism. Warm advection will start to
increase over the western Piedmont, on the eastern flank of a
prefrontal LLJ over the Tenn Valley. Most of the associated rain
will be west of the mountains, but their could be a few areas in
the Foothills and flirting with the western piedmont by Tuesday
morning.  Lows 42-46.


As of 220 PM Sunday...

Models continue to come into better agreement with the overall
pattern through Friday. There are still small timing issues and
differences in precip chances/timing over central NC. Generally,
expect multiple rounds of wet weather with dry periods in between.
Timing and amounts are still a challenge. The weather could get very
interesting for late next weekend and early the following week.

Tuesday through Wednesday Night: The wedge will probably linger
through early Tuesday, however the models erode it by the aft/eve as
the return flow from the high offshore and the southerly flow ahead
of the approaching front both increase. Meanwhile aloft, the
remnants of a closed low over the Baja gets absorbed into the
northern stream as a shortwave that swings through the Great Lakes
through and into the Mid-Atlantic Wednesday/Wednesday night. The
wave should be strong enough to dampen/suppress the ridge. The
surface low and attendant front will approach the area Tuesday
night, swinging through by late aft/eve Wednesday. As a result,
expect best chances for rain to be late Tuesday through Wednesday
from west to east. Temperatures will be above normal, slightly cooler
in the NW Tuesday (mid to upper 50s), but otherwise expect highs in
the 60s and lows in the mid 50s Tuesday night. With the expected
frontal passage late Wednesday, overnight lows will be lower, mid
40s north to around 50 degrees south.

Thursday through Friday Night: There is surprising agreement between
the models for this period, though there are some differences, the
pattern is similar. Expect two additional rounds of precipitation
during this time, with a period of dry weather in between. A fleeting
surface high and upper level ridge will move through/build over the
area Thursday while another low moves out of the desert southwest
northeast toward the Great Lakes. The moisture advection into the
Gulf coast states Thursday night combined with the sufficient
forcing from the low will result in another round of rain moving
into the Carolinas from the southwest Friday/Friday Night.
Temperatures should be fairly steady during this time, highs in the
upper 50s to mid 60s and lows in the 40s.

Saturday and Sunday: This part of the forecast period gets quite
interesting and the model agreement make it even more ominous.
Although, this far out it is hard to jump on board completely.
Fingers crossed for some changes. As of the latest model runs, a
strong low will come onshore in the Pacific NW Friday/Friday night
digging a trough south and east toward TX Saturday and Sunday. In
the wake of the low that moves through Central NC Friday night, a
ridge builds aloft over the southeast U.S. while the surface low
strengthens over the Midwest. Very strong southerly flow advects
very warm moist air into the Gulf Coast states late in the weekend.
There is a bit of uncertainty whether a CAD wedge will set up and
hold over NC or not and thus temperatures are low confidence, but do
expect increasing chances for rain late Sunday into early in the


AS OF 1230 PM Sunday...

VFR parameters across central NC this afternoon will deteriorate
this evening as a blanket of low stratus develops over the region.
This deck of MVFR ceilings should begin between 00Z-04Z, with
widespread MVFR ceilings by 06Z. In addition, should see patches of
light rain develop over the western Piedmont after 00Z,some of which
will cross the KINT and KGSO terminals. This added moisture will
likely lower ceilings into the IFR category in the Triad after 06Z.

The adverse aviation conditions with IFR/MVFR ceilings will persist
through Monday and into Monday night. Ceilings may temporarily lift
into the VFR category later Tuesday. However, aviation conditions
will likely tank Tuesday night into Wednesday as a cold front
approaches and crosses our region. Behind the front, VFR conditions
anticipated for Thursday and Friday.




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