Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 141732

Area Forecast Discussion
National Weather Service Raleigh NC
1235 PM 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.


As of 955 AM Saturday...

A big change from 24 hours ago as northeasterly near sfc flow has
advected a much colder air mass into central NC. This colder air
mass coupled with extensive cloudiness will yield afternoon
temperatures in the mid-upper 40s north to the lower 50s south.
These temperatures are a solid 25 degrees colder compared to the
balmy 70s/near 80 experienced yesterday.

Patchy light rain skirting east across the northeast Piedmont-
northern coastal plain this morning was associated with modest waa
on top of the cool stable air mass at the surface, and a weak
perturbation aloft that is crossing to our north. The chances for
light rain will dwindle to less than 20 percent by early afternoon.

Some thinning of the low clouds may occur this evening as the flow
just above the surface becomes westerly in the wake of the exiting
perturbation. The diminishing cloud cover may prompt the formation
of patchy fog overnight. Additionally, another perturbation passing
to our north may trigger a few sprinkles across the northern
counties. Min temps generally in the 40-45 degree range.


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.


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.


AS OF 1230 PM Saturday...

Widespread MVFR ceilings will persist across central NC this
afternoon, then a gradually lifting/dissipating of the lower
ceilings is anticipated this evening. By 03Z Sunday, VFR conditions
are expected. This improvement in aviation conditions will be brief
as areas of MVFR/IFR visibility due to fog will develop after 06Z
Sunday with pockets of LIFR fog possible, mainly in vicinity of the
Triad terminals and near KFAY. Once the fog lifts later Sunday
morning, VFR conditions should occur.

The passage of another cold front Sunday night will likely initiate
another round of MVFR ceilings that may linger well into Monday.
An unsettled weather pattern will bring a variety of aviation
ceilings to central NC Monday through Thursday. Prolonged periods of
sub VFR ceilings appear probable Monday night through at least
Wednesday/Wednesday night though there will be 3-6 hour windows of
VFR parameters, though timing of such windows highly uncertain at
this time.




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