Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 280207

Area Forecast Discussion
National Weather Service Raleigh NC
1007 PM EDT Thu Oct 27 2016

A cold front will settle south into NC late tonight through early
Fri. High pressure will follow and extend across the Carolinas
through the weekend.


As of 1000 PM Thursday...

00Z RAOB and VWP data across the Carolinas this evening depict
pronounced veering of the wind in the lowest 500 mb, and implied WAA
and contribution to QG forcing for ascent. This WAA regime is
occurring on the SRN periphery of a pronounced shortwave trough
moving E across far SERN Ontario, whose focused height falls aloft
will continue to pass well N of central NC. Within the WAA regime, a
narrow ribbon of low-mid level moisture and associated transport,
capped above by an inversion around 12 k ft, and sampled well by
both the RNK and GSO RAOBs, will progress steadily E across central
NC during the next several hours, then offshore by 12Z.

This moist axis will maintain a chance of a few (widely scattered)
showers over the NE Piedmont and Coastal Plain through around 06Z,
with dry conditions otherwise and elsewhere. Since the surface cold
front accompanying the aforementioned shortwave trough remained
along and west of the Appalachians from ERN WV to ERN TN and NRN AL
at 02Z --and it will likely not settle into even the NRN NC Piedmont
until around daybreak-- it will be a relatively mild night. Lows
mainly in the middle 50s to lower 60s.

A steady light SSW surface wind will limit the potential for fog
development tonight, despite otherwise favorable conditions that
include clearing behind the aforementioned low-mid level moist axis
and seasonably high pre-frontal surface dewpoints around 60 degrees.


As of 245 PM Thursday...

In the wake of the trough crossing the area today, the cold front
will settle south into SC as brief cold advection pushes
thicknesses down to around 1360. This will offset what is
otherwise full heating with high pressure building across the
central Appalachians. Prefer a blend of MOS values here - 69 to 76
from northeast to southwest.

High pressure will settle overhead Friday night, yielding optimal
radiational cooling conditions. Most of the blended guidance looks
a little too warm given thicknesses and cooling potential, so
will opt for MOS values here as well - 44 to 49.


As of 245 PM Thursday...

Primary storm track will follow the main belt of westerlies that
will shift northward along the US/Canada border as upper level ridge
over the Central Plains expands eastward into the Southeast US.

This will favor a continuation of dry conditions with temperatures
well-above normal, averaging a good 7 to 12 degrees above normal
through next week, potentially peaking Sunday with the potential for
near record warmth in the lower to mid 80s possible in advance of a
dry and weak back-door cold front late Sunday night. After a brief
cool down to more seasonable temps on Monday, temperatures will
quickly warm back into the mid 70s to lower 80s by Wednesday.

Significant discrepancies begin to show up in both the probabilistic
and deterministic model guidance late next week, with the GFS
retrograding the upper level ridge far enough west to allow a back-
door cold front to push south into the area late Thursday, while the
ECMWF keeps the upper ridge in place over the region and keeps the
front north of the area.


.AVIATION /00Z Friday through Tuesday/...
As of 815 PM Thursday...

VFR conditions will dominate for the next several hours and into the
overnight hours at all sites, although a period of sub-VFR
conditions is possible 08z-12z. A band of showers currently crossing
northern portions of the forecast area may bring a brief shower to
RDU/RWI through 04z, although cigs and vsbys should remain mostly
VFR. Winds will remain light from the SW at speeds under 7 kts
through much of the night, ahead of a cold front dropping into the
area from the NW. Lingering low level moisture and light winds ahead
of this front will bring about a chance for IFR vsbys and low
shallow stratus late tonight. Models are quite variable in depicting
any such sub-VFR conditions, leading to lower than usual confidence.
The GFS favors late-night/early-morning stratus/fog at RDU/RWI,
while the HRRR hints at such conditions confined to the INT/GSO
areas, and the NAM indicates just MVFR fog at all locations. Based
on the steady stream of mid and high clouds heading into the area
from the WNW which could inhibit radiational cooling and limit fog
development, will lean toward the HRRR, with IFR conditions
restricted to INT/GSO, as the front is only expected to drop into
the VA border counties toward daybreak. All clouds will clear out
Fri morning, with VFR conditions highly likely thereafter, and
surface winds becoming light from the north as the front drops

Looking beyond 18z Fri, high pressure will build in Fri through Sun,
leading to a high confidence in VFR conditions and light surface
winds, although there is a small chance of shallow fog Sat and Sun
mornings near dawn, especially near bodies of water. A weak front
will drop through late Sun night/Mon morning, which may bring a
period of MVFR cigs Mon into Mon night, but this risk appears low at
this time. -GIH




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