Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 240311

Area Forecast Discussion
National Weather Service Raleigh NC
1010 PM EST Tue Jan 23 2018

An area of high pressure and attendant seasonably cool air mass will
build into and settle over the region Wednesday and Thursday.


As of 1010 PM Tuesday...

A secondary cold front, which marks the true density airmass change
and easiest discernible by dewpoints falling into the 20s, has just
recently pushed through the Triangle, and will continue to progress
SE through the remainder of the forecast area over the next 3 to 4
hours. Meanwhile, winds have dropped off considerably, with only
sporadic wind gusts into the teens being reported.

Under clear skies, resultant CAA will govern overnight lows,
ranging from lower 30s over the western Piedmont to mid/upper 30s
across central and eastern areas.


As of 250 PM Tuesday...

Wednesday and Wednesday night, high pressure at the surface over the
southern Plains will build east across the Deep South and into the
Carolinas. Meanwhile, an upper level disturbance will drop sewd from
the Great Lakes toward the Mid Atlantic. This system will cause
patchy high level clouds to stream out ahead of it. Still, expect a
decent display of sunshine Wednesday. Warming the low level
atmosphere dry adiabatically to 900-875mb layer achieves afternoon
temperatures in the low-mid 50s. The disturbance will pass to our
north Wednesday evening. This feature will likely maintain light
mixing at the surface through the early overnight hours. This mixing
may aid to keep temperatures up a bit, until the sfc winds decouple
close to dawn. Min temps generally 25-30 degrees.

The sfc high builds/extends overhead Thursday, maintaining mostly
clear skies. Warming the lower atmosphere dry adiabatically to 850-
825mb yields afternoon temperatures once again in the low-mid 50s.
Another cool night Thursday night as the sfc high remains overhead
or near the coast. Min temps mid-upper 20s.


As of 215 PM Tuesday...

Friday and Saturday: Rising heights are expected during the period
as short wave ridging aloft builds into the region. Surface
high pressure centered near the mid-Atlantic coast Friday
morning will shift offshore allowing a strengthening southerly
flow to develop. Mainly sunny skies with just some high clouds
are expected on Friday. As the deep layer flow becomes more
southwesterly, increasing moisture will lead to an increase of
multiple cloud layers on Friday night and especially Saturday.
Highs will range in the mid 50s to around 60 on Saturday with
lows in the lower to mid 30s on Friday night. Highs on Saturday
will warm into the lower to mid 60s on Saturday.

Saturday night through Monday: The pattern becomes more active but
uncertain for the the late weekend as a broad eastward
advancing upper level trough reaches the Plain on Saturday. The
trough will amplify as it moves into the Mississippi Valley
Sunday morning and then continues east reaching the southern
Appalachians on Monday morning. Deep layer moisture will
increase with precipitable water values exceeding an inch by
Sunday morning. While the broad pattern and features are
generally consistent across the NWP suite, notable differences
are apparent in the details. In general, the guidance has
trended slower and more amplified. The operational EC has
consistently been slower, deeper and wetter with the system as
it impacts central NC than the GFS. The last couple runs of the
GFS have trended toward the EC and a slower/more amplified
pattern is supported by WPC. Given this, have leaned heavily
upon the EC and the WPC guidance for forecast details. Have
slowed PoPs and increased them with the greatest chance on
Sunday afternoon. The developing surface way shifts offshore on
Sunday night with the precipitation all over by Monday morning.
WPC rainfall guidance suggests around three quarters of an inch
of precipitation is possible, more to the north and west, less
to the south and east.

Quiet weather returns for later Monday and Tuesday as upper level
heights begin to rise and surface high pressure builds into the
area. Highs will range in the lower to mid 50s with lows
generally in the upper 20s to lower 30s. -Blaes


As of 615 PM Tuesday...

VFR+ conditions have returned to all TAF sites, with improving
aviation conditions expected over the remainder of the period. Gusty
westerly winds will continue to diminish during the early part of
the overnight hours, with mostly clear skies expected to persist
into Wednesday evening. High confidence during this period of the

High pressure will build into the region tonight and settle overhead
late Wednesday into Thursday, continuing the period of VFR
parameters. VFR conditions expected to last through late Friday.
There will be a chance for MVFR ceilings Saturday as an approaching
cold front will induce a sly flow over the Carolinas. This flow will
tap moisture from the Gulf and transport it nwd into our region,
aiding to increase the cloud coverage. As the front gets closer
Saturday night into Sunday, the threat for scattered showers and
MVFR parameters will increase.



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