Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 092036
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
335 PM EST Fri Dec 9 2016

.SYNOPSIS...
Arctic high pressure will build across the area through Saturday. A
cold front will approach from the west late Sunday and move through
the area on Monday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 240 PM Friday...

A chilly day (temps around 12-15 deg below normal) will become a
chilly night, as arctic high pressure continues to build into the
area from the NW. Passage of a weak sheared wave just to our north
will bring a few high clouds mainly to the northern forecast area
overnight (some of this cloudiness could be orographically enhanced
late). But otherwise skies will be generally clear tonight, and this
in combination with light surface winds will foster good radiational
cooling, with thicknesses likely to be a bit lower than they were
this morning. Expect temps to bottom out in the 18-24 degree range,
with the cooler readings in outlying areas of the northern/western
Piedmont. -GIH

&&

.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 FRIDAY/...
As of 210 PM Friday...

Initial low amplitude long wave troffing will produce fast and near-
zonal flow across the central and southern tiers of the Conus
through mid week. Return flow ahead of an initial front on Monday
will produce a strong surge of warm air advection with highs ranging
from upper 50s across the north to mid 60s in the south...5 to 10
degrees above normal. Moisture advection will cut off pretty quickly
as low level flow turns westerly across the Gulf states...with
chance PoPs during the day shifting to the east and diminishing
post-fropa on Monday night.

The frontal zone aligns parallel to the flow and forecast details
are murkier heading towards midweek with considerable variablity in
model solutions. The frontal zone looks to remain south of the
area...with small chance PoPs mainly across the southern tier...
both Tue and Wed as surface high pressure races across the Ohio
Valley. Highs will be on a gradual fall as the upper trof amplifies
a bit and we should be in a predominantly cloudy regime. Highs
Tuesday in the mid to upper 50s will fall to the low and mid 50s on
Wednesday.

Confidence in model solutions for the late week is even lower
although  colder air will continue edging southward. The upper flow
is not highly amplified, however, which will block off the really
frigid airmass north of the area. Regardless, highs will probably
top out in the mid 40s after morning lows in the mid to upper
20s both Thu and Fri.

&&

.AVIATION /18Z Friday through Wednesday/...
As of 120 PM FRIDAY...

High confidence in chilly but tranquil aviation conditions for the
next 24 hours. Skies will be virtually cloud-free with unrestricted
vsbys for the rest of today through tonight and into Saturday as
high pressure builds in from the NW. Only a few high clouds tonight
are expected as a weak mid level wave passes by within a fast flow
aloft.

Looking beyond 18z Saturday, VFR conditions should hold through the
first half of Sunday as high pressure builds overhead. As a warm
front approaches from the south, moisture will increase, and cigs
will trend to MVFR then IFR Sunday afternoon from south to north.
There is a good chance for low level wind shear conditions Sun night
into Mon morning with 35-40 kt winds from the SW at 1500-1800 ft
AGL. Adverse aviation conditions, including sub-VFR cigs and vsbys,
are expected to dominate from late Sunday through at least Monday
night -- and perhaps into Wednesday -- as waves of low pressure
track along the frontal zone as it holds over or just south of the
area. -GIH

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SYNOPSIS...CBL
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...mlm
AVIATION...Hartfield



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