Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 221804

Area Forecast Discussion
National Weather Service Raleigh NC
105 PM EST Mon Jan 22 2018

A cold front will approach from the west today, and cross central NC
Tuesday morning. High pressure and associated seasonably cool and
dry conditions will follow for mid-week.


As of 1025 AM Monday...

Just minor tweaks made to the near term forecast, mainly around
timing of scattered showers later this evening.

12Z upper air analysis along with satellite imagery depict a deep
and mature cyclone over the central Plains. This system projected to
lift newd as strongest winds aloft have rounded the base of the
upper level trough.

While the atmosphere over central NC remains relatively dry, flow
above 400mb advecting enough moisture to produce a veil of high
clouds overhead. This deck of high clouds currently thick enough to
inhibit sunshine across the Piedmont, though looking upstream, some
thin spots noted. Thus, some potential for at least partly sunny
skies this afternoon. This warmth along with a steady sly low level
flow should allow temperatures to recover into the 60s this

The aforementioned sly flow will advect enough moisture to support
the formation of stratocu deck late this afternoon, mainly south of
highway 64. As the atmosphere continues to moisten, could see an
isolated shower or two streak nwd across the region after 4 PM.
Latest near term model guidance has slowed the arrival of the better
lift of showers until 06Z or later. So have delayed the timing of
higher pops a few hours across the western Piedmont this evening.


As of 400 AM Monday...

Tonight: A warm front and associated leading edge of surface
dewpoints in the 50s will surge nwd across cntl NC tonight, with low
temperatures likely to occur during the mid-evening hours, before
slowly rising overnight. Despite the increasing surface theta-e,
bufr forecast soundings suggest a shallow, near-surface stable layer
will likely remain in place, thereby muting surface-based
instability and threat of severe weather overnight. Nonetheless,
HREF mean MUCAPE values are forecast to climb to around 250 J/kg
between 06-12Z, in a strong WAA regime driven by a 45-60 kt sswly
llj at 925-850 mb. As such, scattered to numerous (slightly
elevated) showers are apt to develop and overspread cntl NC, along
the axis of the llj, overnight.

Tuesday: The warm front will be quickly followed by an effective
(lead) cold front forecast to cross cntl NC between 12-15Z over the
nw Piedmont and between 18-20Z over the Coastal Plain. The passage
of this cold front --one that may be better characterized as a dry
line, and accompanying broken line of convection-- will result in
clearing, drying the in the low levels, and the deepening of a
diurnal mixed layer that will promote the development of strong
sswly winds and associated gusts that will peak in the 30s kts per
bufr forecast soundings.

In addition, some realization of weak surface-based instability may
occur ahead of the convective line with diurnal heating, mainly east
of Hwy 1, though widespread pre-frontal cloudiness will limit this
heating and associated destabilization, to a several hundred J/kg or
less. Nonetheless, a few strong convective wind gusts will be
possible as the line moves east. Any appreciable cooling will lag
this feature and not occur until a secondary front settles sewd
across cntl NC after 21Z. High temperatures will consequently again
climb into the 60s, to lwr 70s over the sern CWFA. Storm total
precipitation amounts are expected to be around a tenth to quarter
inch on average, and scattered, so a widespread soaking rain is not


As of 210 AM Monday...

Expect dry weather through Friday night. An upper level shortwave
and a reinforcing dry cold frontal passage is expected Wednesday
night/Thursday. Surface high pressure is expected to build into the
area in the wake of the secondary cold front and remain over the
area into Saturday. The upper level ridge will move eastward over
the Carolinas through Friday night. Another upper level trough and
surface cold front will develop over the Midwest and progress
eastward toward the Mid-Atlantic over the weekend. As southwesterly
flow increases, so will the warm, moist advection into the region.
As a result, cloud cover and chances for precipitation will increase
late Saturday into Sunday as the cold front approaches. As of the
latest forecast cycle, the front progresses through Central NC by
Sunday night, with cool high pressure building in behind it. Highs
will be generally in the upper 40s north to mid 50s south through
Friday and lows in the upper 20s to low 30s Wednesday and Thursday
nights. Temperatures will moderate through Sunday, cooling down once
again in the wake of the front.


As of 105 PM Monday...

While VFR parameters will persist through 21Z across central NC, an
approaching frontal system will bring an increased threat for
adverse aviation conditions to central NC tonight into Tuesday.

A sly flow will advect enough low level moisture to cause a deck of
stratocu to develop and progress nwd late this afternoon and this
evening. This deck of MVFR ceilings will likely encroach upon the
KFAY vicinity by 21-22Z, and across the remainder of the TAF sites
between 00Z-04Z. A low level jet will strengthen overhead this
evening and into the overnight. While sfc winds at the sfc will be
sly 8-12kts, winds just above the sfc (~1000-1500ft AGL) will be sly
45-50kts, creating low level wind shear conditions. The frontal
system will be just west of our region prior to daybreak leading to
an increase in shower activity across the western Piedmont including
the Triad terminal by 06Z, and in proximity of KRDU and KFAY by 09Z.
Per latest model soundings, enough instability may reside aloft to
support a thunderstorm or two, primarily between 08Z-14Z.

The cold front will sweep eastward across our region early Tuesday
morning. Rapid clearing is anticipated, leading to VFR parameters in
the Triad vicinity shortly after 12Z, and in proximity of KFAY and
KRDU by 15Z, and KRWI by 16Z. Sfc winds will remain blustery ahead
and behind the front with southwesterly sfc winds frequently gusting
25-35kts, with sporadic gusts 40-45kts possible. The strong wind
gusts should subside after 21Z Tuesday.

VFR parameters expected Tuesday night through Saturday morning as
high pressure will be the main influence on our weather. Another
frontal system will begin to impact the Carolinas late Saturday into
Sunday, possibly leading to a period of sub-VFR parameters.




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