Area Forecast Discussion Issued by NWS Raleigh/Durham, NC
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FXUS62 KRAH 180816
AFDRAH
Area Forecast Discussion
National Weather Service Raleigh NC
416 AM EDT Mon Mar 18 2024
.SYNOPSIS...
A cold front pushing southeast through the region will settle to our
southeast this morning. A stronger second cold front and upper level
disturbance will cross the area late today, bringing cooler air for
tonight through Tuesday as Canadian high pressure builds in from the
west and southwest. Milder temperatures return for Wednesday as the
high shifts to our south.
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.NEAR TERM /TODAY THROUGH TONIGHT/...
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As of 400 AM Monday...
...A Freeze Warning has been issued for portions of the Southern
Piedmont and Sandhills for sub-freezing temperatures tonight...
Surface observations as of 07z show a cold front extending from
southeast VA through the Triangle and down towards the Charlotte
area. This front marks a sharp gradient in dew points with low 50s
ahead to mid 20s behind. This front along with periodic winds gusts
15 to 20 mph will continue to march through central NC through early
this morning before shifting offshore by sunrise. This initial surge
of noticeably drier and slightly cooler air will be a precursor to a
secondary surge of cold air and another cold frontal passage
expected this evening through early tonight (See Fire Wx section
below for more information related to fire concerns). A deep and
positively tilted trough axis will pivot across the Ohio Valley this
morning and begin taking on a neutral tilt as the base of a
significant PV anomaly swings through the southern Mid-Atlantic this
evening through midnight. The core of the PV anomaly will have a
favorable track right over central NC to produce strong synoptic
forcing for ascent which will lift the inversion at 700mb and result
in mid-level clouds blossoming over central NC. Mid-level ascent
will be amplified by 700-500mb FGEN during this time, but should
result in mostly virga across the area with only isolated locations
able to sufficiently measure precipitation thanks to a deep inverted-
V signature in the boundary layer and large dew point depressions.
Much cooler air will filter in behind the Arctic cold front
throughout the night and allow for temperatures to drop well into
the 30s by early Tuesday morning. Yesterday marked the first
day of the growing season for the southern Piedmont, Sandhills,
and central/southern Coastal Plain. As such, the Freeze Watch
has been upgraded to a Freeze Warning over the areas where
confidence is sub- freezing temperatures is highest. Although
not in the Freeze Warning, a large portion of the Northwest
Piedmont, Northern Piedmont will also likely see sub-freezing
temperatures and any early-budding vegetation will also be at
risk of damage from sub-freezing temperatures.-- End Changed Discussion --
&&
.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 200 AM Monday...
The potent mid level PV max will have shifted offshore by Tue
morning, and while another much weaker perturbation will shift ESE
through the Mid Atlantic Tue afternoon, it won`t have any moisture
to work with, as the mid levels continue to warm and stabilize
within deep subsidence. Little more than a streak of high thin
clouds is expected Tue afternoon, with the remainder of the area and
of the period largely cloud-free as surface high pressure builds
across the Gulf and Southeast states and eventually spreads E off
the Southeast coast. Our NW or WNW surface flow early Tue will back
quickly to SW and remain rather stout and gusty, given the MSLP
gradient between the W-E surface ridge to our S and a northern
stream cold front dropping into the Ohio Valley and approaching our
area from the NNW late Tue night. This will set up a lee trough over
the W Piedmont that will persist Tue/Tue night, but again, the lack
of moisture will make this inconsequential. With low level
thicknesses having bottomed out around 50 m below normal Tue
morning, some recovery will begin Tue as the SW flow develops,
however Tue will be our coldest day of this stretch, given the cold
start and the somewhat shallow BL beneath the growing subsidence
inversion aloft. Expect highs in the 50s. Radiational cooling should
be better, although not ideal, Tue night with clear skies and
lighter winds, supporting decoupling by late evening. Expect lows in
the mid 30s to around 40, with the risk of another freeze night
rather low and confined to just the typically cooler rural/outlying
central Piedmont for which the growing season has not yet officially
begun. -GIH
&&
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 230 AM Monday...
Overview: Some uncertainty persists regarding late-week rain
chances, but late Thu night through late Sat appears to be the time
frame with the better chances, likely peaking Fri/Fri night across
the S and E. Forecast confidence in both temps and rain chances
plunges over the weekend. Near to above normal temps Wed will drop
to below normal then persist through the weekend, with Thu/Fri as
the coolest days.
Wed/Wed night: Very nice day expected. With a dry and stable column
persisting through Wed, expect lots of sunshine with WAA, which
should push temps up to the upper 60s to mid 70s, with gusty SW
winds, meaning the early-season pollen will be flying. Models
continue to depict a backdoor cold front dropping SSE into or
through NC Wed night, driven by a passing shortwave trough through
the Northeast/New England and incoming dense air associated with the
cold high pushing from Manitoba/W Ontario into the Upper Midwest and
Great Lakes. Thus, our temps should drop back to near to slightly
below normal Wed night, esp across the N, with lows from the mid-
upper 30s near the VA border to the low-mid 40s S.
Thu-Sun: Conditions become increasingly unsettled late in the week
as the upper low over the Desert Southwest this morning will have
finally opened to a shortwave trough and begun to shift eastward,
tracking from OK/N TX Thu morning across the lower Miss Valley
through Fri morning and into the Southeast and Carolinas by Fri
night. While most models depict this wave starting to dampen by this
time, their solutions diverge Fri-Sun in terms of timing and
amplitude, producing sensible weather differences. The latest
GFS/GEFS are deeper and faster (a result of a deeper polar low
crossing S Ontario, causing our wave to shift quickly off the Mid
Atlantic coast Sat morning, albeit with a lagging trailing trough
over/off the FL E Coast), while the Canadian/ECMWF and older
GEFS/GEPS also maintain some amplitude but are slower, reasonable
given their weaker and further-north polar low, resulting in an
overall weaker steering over the SE quarter of the CONUS as longwave
troughing starts to dig down the West Coast. The latter camp and its
weak upper low holding over the E Carolinas suggests lingering
clouds and rain chances persisting, mainly E, while the faster GFS
indicates clearing/drying and warming over the weekend. The newer
GEPS/ENS are a good compromise, showing a slowing wave over the
Carolina coast through Sat followed by an eastward push with
incoming shortwave ridging Sun, and will follow this path with the
forecast. Will have fair skies Thu with dry weather through the
evening, then spread chance to low-end likely pops (highest S/E) Fri
morning, peaking in the afternoon through night, before shifting
pops to mainly in the Coastal Plain Sat with drying late Sat night
through Sun. Expect slightly below normal temps Thu behind the
backdoor front. As the rain arrives Fri, the surface high to our N
and NE will have pushed off the Mid Atlantic coast but still extend
back into the Piedmont with lower pressures over GA/FL/SC. This
should set up a brief CAD event as the rain locks in the stable air,
and as such, have knocked temps down over much of the Piedmont Fri.
Will have highs in the lower 50s NW ranging to the low-mid 60s SE.
These NW readings are several degrees below most guidance, and may
not even be cool enough, however the high is not centered in a good
spot (off the Mid Atlantic coast) to provide a steady feed of cooler
air/lower dewpoints, so will stick with these more modest
adjustments for now. After low pops mainly E Sat, will trend them E
and out Sat night/Sun, with temps slightly below normal. -GIH
&&
.AVIATION /08Z MONDAY THROUGH FRIDAY/...
As of 200 AM Monday...
VFR conditions are expected through the 24 hour TAF period. A cold
front and wind shift is currently making its way through central NC
and is forecast to reach RDU by 07-08z and RWI/FAY by around 09z.
Winds will increase out of the NNW 10-15 kts for a couple hours post
fropa. Winds will shift back generally out of the west Mon afternoon
ahead of another stronger cold front forecast to move through
central NC from 22-03z. Surface winds will again veer out of the NW
around 15 kts sustained with gusts 20-30 kts. Gusts will gradually
weaken, but should continue through most of the night into early
Tues morning. Some light rain, but mostly virga, will be possible as
a 5-8k ft cloud deck blossoms over most of central NC Mon evening
through midnight.
Outlook: LLWS will be possible Tues night into early Wed as winds at
2k ft increase to 30-40 kts. A dry cold frontal passage will bring a
wind shift out of the NW late Wed into early Thurs. A storm system
approaches the area Fri into Sat bringing a high chance for sub-VFR
conditions.
&&
.FIRE WEATHER...
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Mon evening: Take extra precaution to extinguish any fires this
afternoon ahead of the frontal passage this evening into
tonight. Dew points in the low 20s to teens with temperatures
still in the 50s late this afternoon will result in RH values in
the low to mid 20s with westerly winds increasing to 10-15 mph
and gusts up to 20 mph. Any fires that start today will be at
risk for spreading and rapid change in direction as the strong
cold front moves into the NW Piedmont this evening with
sustained winds around 15 mph and gusts up to 30 mph behind the
front.
Wed: Ahead of a dry cold frontal passage, southwest winds will
increase to 10 to 15 mph sustained with gusts up to 25 mph Wed
afternoon. Temperatures rising into the upper 60s to mid 70s
with dew points in the upper 20s to low/mid 30s will result in
Min RH in the 20s.-- End Changed Discussion --
&&
.RAH WATCHES/WARNINGS/ADVISORIES...
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Freeze Warning from midnight tonight to 9 AM EDT Tuesday for
NCZ073>076-083-084.-- End Changed Discussion --
&&
$$
SYNOPSIS...GIH
NEAR TERM...Swiggett
SHORT TERM...GIH
LONG TERM...GIH
AVIATION...Swiggett
FIRE WEATHER...Swiggett