Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 211427

Area Forecast Discussion
National Weather Service Raleigh NC
925 AM EST Mon Jan 21 2019

Arctic high pressure will build into central NC today, and drift
overhead tonight through early Tuesday. This high will drift
offshore Tuesday night, permitting a slightly warmer air mass to
overspread the region. An approaching area of low pressure will
cause unsettled weather conditions Wednesday into Thursday.


As of 925 AM Monday...

Forecast is in great shape, with cold high pressure ridging sitting
over the area. After morning lows in the teens to lower 20s, temps
have been slow to rise within a CAA regime. The 12z GSO sounding
shows a well-mixed BL up to 900 mb, facilitating a steady breeze
from the NW and N, which is helping to push wind chills down into
the single digits to mid teens. Based on upper air analyses and high
res guidance, periodic gusts over 20 mph will persist into the
afternoon, particularly across the E and SE where a decent MSLP
gradient remains. Temps still appear likely to peak in the upper 20s
to mid 30s, based on current pace and an eventual decrease in winds
under bright sunshine. -GIH

Earlier discussion from 335 AM: Arctic high pressure centered over
the Great Lakes early this morning will continue to build/extend
southeastward into central NC today. The core of the coldest air
will also extend into our region, resulting in temperatures this
afternoon as much as 20 degrees below normal. Most locations across
the northern Piedmont and northern Coastal Plain will fail to warm
above freezing this afternoon. In the immediate near term, blustery
NW sfc winds with gusts around 20 mph will continue this morning.
These winds coupled with the very cold air will yield wind chill
values this morning in the single digits across the north, and close
to zero near the Virginia border. Wind chill values across the south
will be in the neighborhood of 10 to 15 degrees above zero. Plan to
issue a SPS shortly to cover this issue. These winds will gradually
subside this afternoon, likely decoupling close to sunset. Sfc
dewpoints this afternoon will likely get as low as 5 to 8 below
zero, characteristic of an arctic air mass.

Tonight, the core of the high pressure will settle overhead. Under
clear-mostly clear skies and a light/near calm wind regime,
temperatures will tumble back into the teens areawide. Potential for
the normally colder locations such as Henderson and Louisburg report
a morning low 8 to 12 above.


As of 335 AM Monday...

As the sfc high drifts eastward Tuesday, the low level flow will
become more east-southeast and begin to modify the arctic air mass.
After the chilly start to the day, temperatures will likely recover
a solid 20-25 degrees with afternoon highs in the upper 30s to lower

The atmosphere will continue to modify Tuesday night as the low
level flow just above the surface strengthens, leading to isentropic
upglide/lift. Latest model guidance currently depicting enough
moisture depth and lift to generate patchy light precip
overnight/early Wednesday across sections of the western Piedmont.
With temperatures hovering near or slightly below freezing, and
precip falling through the sub cloud layer leading to some
evaporative cooling, potential for spotty light freezing rain or
freezing drizzle to occur. While ice accrual will be very limited,
could see enough precip fall to result in a few slick spots on
elevated surfaces just prior to the start of the morning commute
Wednesday across the western Piedmont, including sections of the
Triad. Plan to highlight this threat in the hazardous weather
outlook product.


As of 150 AM Monday...

Wednesday and Thursday: The upper level ridge will shift eastward as
the upper level trough approaches from the west. Multiple shortwave
disturbances will develop and migrate northeastward along the trough
while the eastward shifting ridge gives way to deep southwest flow
into the region. The surface high will also shift eastward over the
Atlantic, resulting in southeasterly return flow into central NC off
the Atlantic. The ridge will linger over the area into the day
Wednesday before being eroded completely by the advancing frontal
system. The lingering wedge airmass combined with the overrunning of
warm moist air above it will result in some light precipitation,
likely in the form of rain or freezing rain early Wednesday,
becoming all rain by mid-morning. As the cold front approaches from
the west, the south-southwesterly flow will advect warm moist air
into the area from the Gulf. The result will be increasing clouds
and precipitation chances from the west. However, aside from some
light stratiform showers, the main axis of pre-frontal precipitation
could hold off until Wednesday night, especially over the eastern
portions of the area. While the parent surface low is expected to
move through the Great Lakes and into Canada before the front pushes
into the region, a secondary low, strengthened by a developing
shortwave aloft, will develop along the front over the Appalachians
and NC Piedmont as the front pushes into the area. Best chances for
rain across central NC will be Wednesday night through Thursday
afternoon ahead of the cold front as it pushes through the area.
Largely expect the front to be through the area by midnight Friday.
With the southerly flow advecting warmer air into the area ahead of
the front, highs will range from around 50 degrees in the NW to mid
60s SE on Wednesday and Thursday. Overnight lows in the mid 40s to
mid 50s expected Wednesday night. Thursday night temperatures will
depend on the fropa timing, but for now generally expect lows in the
upper 20s NW to mid 30s SE.

Friday through Sunday night: Expect a return of cooler, drier
weather in the wake of the cold front, with highs in the 40s on
Friday. A reinforcing dry cold front Friday night combined with the
surface high over the area will result in lows Friday night in the
upper teens to mid 20s and highs Saturday in the mid 30s to mid 40s.
Overnight lows will generally be in the 20s and highs in the 40s
expected through the remainder of the period.


As of 635 AM Monday...

There is a high probability that VFR parameters will occur across
central NC through 12Z Tuesday. Sfc winds will remain blustery this
morning with gusts 20-25kts common. Sfc winds will subside to less
than 10kts prior to 00Z Tuesday.

A slightly warmer and more moist air mass will advect into central
NC from the south late Tuesday night. This will likely result in the
development of a low stratus deck, primarily over the western
Piedmont, after 06Z Wednesday through Wednesday morning. If lift is
strong enough and the moisture deep enough patchy light precip may
occur close to daybreak near or south of the Triad terminals. With
sfc temperatures hovering near or just below freezing, spotty light
freezing rain or freezing drizzle may pose a threat.

An approaching low pressure system will bring unsettled weather
conditions to central NC Wednesday through Thursday. This will
likely result in sub VFR ceilings and areas of rain across central
NC. Improving aviation parameters anticipated for the end of the
work week.




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