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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 201448
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1045 AM EDT Wed Mar 20 2019

.SYNOPSIS...
Continental polar high pressure will extend southwestward across the
middle Atlantic and interior Carolinas today. Meanwhile, coastal low
pressure now developing off the north-central SC coast will track
northwestward and inland across eastern NC tonight, then rapidly
deepen up the middle Atlantic coast on Thursday. A pair of strong
shortwave troughs aloft and related surface cold fronts will follow
and cross central NC Thursday afternoon and Thursday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1045 AM Wednesday...

Little adjustment required to the near term forecast. Presence of a
sfc ridge in the vicinity of the far NW Piedmont and attendant dry
air will delay precip onset until later today, so have adjusted PoPS
accordingly.

12Z upper air analysis depicts a narrow region of low level moisture
advection focused across the NC Coastal Plain in association with a
developing area of low pressure off the SC coast. The approach of a
modest mid level perturbation lifting east-northeast from the SE
U.S./northern FL peninsula should serve to strengthen this low this
afternoon. This, in turn should strengthen the onshore flow into the
NC Coastal Plain, leading to deeper moisture and lift. Thus, still
expect areas of light rain to blossom over the Coastal Plain and
Sandhills, and possibly as far west as the Triangle region between 5
PM and 8 PM.

Increasing/thickening cloud cover and patchy light rain expanding in
coverage will limit insolation, inhibiting temperature recovery.
Anticipate highs this afternoon along and east of highway 1 in the
40s. Based on expected arrival of the deeper cloud coverage over the
Triad, still expect highs to reach the low-mid 50s over the far
western-NW Piedmont.

Tonight, lift through the column will increase thanks to a s/w
pivoting newd from the TN Valley into the southern Appalachians. In
addition, central NC will be in the left exit region of a upper jet
streaking across the Deep South. Meanwhile low level moisture will
continue to advect into the eastern sections of our forecast area as
a sfc wave lifts nwd through the NC Coastal Plain. This will lead to
categorical PoPs over the northeast Piedmont-northern Coastal Plain,
with likely PoPs over the remainder of the Sandhills and southern
Coastal Plain, especially this evening. PoPs will quickly dwindle
farther west as moisture depth will not be as great as compared to
the east plus low level convergence will be weaker.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 415 AM Wednesday...

Thursday morning the area of banded precipitation will be heading
well north into Virgina as the dry conveyor belt punches north
across central North Carolina. Most of the area will remain overcast
at this time though as low level saturation remains trapped
underneath the inversion. The brief break in the precipitation will
be short lived as a stronger wedge of DCVA approaches from the west.
A nice fall/rise height couplet will accompany the wave and cross
the zones Thursday afternoon. Mid level thermal profiles will also
begin to collapse as the wave moves overhead allowing showers to
develop across central North Carolina. Further enhancing the already
impressive lift will be a surface cold front. PWATs at this time
are slightly elevated or around 0.58" (just above the mean for
this time of year). Central NC also remains on the divergent side of
the trough axis. Given the above have increased PoPs for Thursday.

Temperatures for Thursday will again be extremely tricky as the low
level clouds hanging around will likely limit highs. The NAM has
highs struggling to get out of the lower 50s with the GFS showing
lower 60s possible. The ECMWF splits the difference. For now have
trended high temperatures down across the area for Thursday, but
this might need to be further lowered.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 345 AM Wednesday...

Dry weather with temperatures slightly below to near normal can be
expected Friday with breezy conditions. Friday morning an upper
level trough axis will be centered over central North Carolina as
the DCVA from the exiting surface low ejects northeast. CAA and deep
mixing are forecast on both NAM and GFS forecast soundings as the
trough axis swings east. A breezy northwest wind Friday afternoon is
indicated as forecast soundings show gusts in the upper 20 mph range
via momentum transfer techniques. Friday night a vertically stacked
upper level low over New England will continue to deepen and push a
reinforcing cold front through the area. Low temperatures Saturday
morning will be in the mid to upper 30s.

During the day Saturday the stacked low over New England will pull
northeast with low level thermal profiles moderating. Given the
slightly further west placement of the low (and therefore trough
axis) have lowered high temperatures a bit for Saturday. Dry weather
will then continue into Sunday as the upper level low exits east.
Right on the heels of the exiting upper level low will be another
potent upper level low diving southeast of the Hudson Bay. This low
will then absorb a weaker upper level low over the Midwest United
States. The GFS is slightly stronger and less progressive with the
upper level low in Quebec than the ECMWF. The CMC is even more
progressive than the Euro. The stronger and less progressive
solution allows the low over the Midwestern United States to be
absorbed with the remnant energy swinging south around the base of
the trough axis. The CMC/ ECMWF solution doesn`t absorb all of the
energy across the Midwest and actually brings a closed low across
the Mid-Atlantic States. The cold front in association with the low
over Quebec crosses central NC the quickest with the GFS solution
(early Tuesday morning) and the slowest with the CMC solution
(Wednesday afternoon). For now have trended the forecast slightly
towards the slower ECMWF and CMC solutions. The next chance of
precipitation (after today/ Thursday) now looks to be delayed until
Monday afternoon. This could be delayed even further if models trend
further towards the CMC solution.

&&

.AVIATION /11Z WEDNESDAY THROUGH SUNDAY/...
As of 715 AM Wednesday...

An area of 3-8 thousand ft ceilings and light rain will continue to
blossom nwwd into cntl NC today, on the northwest side of a coastal
low now developing off the n-cntl SC coast. As lift and moisture
increase/deepen through the afternoon and early tonight, ceilings
will likely lower into MVFR range at KFAY and KRWI prior to 18Z and
KRDU between 18Z-00Z, also roughly coincident with the onset of a
steady light rain. Conditions will lower to IFR or LIFR as the rain
increases in intensity by early tonight; and while the heaviest
steadiest rain will end from ssw to nne between 03Z-06Z, widespread
IFR-LIFR overcast and periods of drizzle will remain through early
Thu. Meanwhile, the wrn edge of the rain and sub-VFR conditions is
likely to bisect the wrn NC Piedmont, including the GSO and INT
vicinity. As such, rain and sub-VFR conditions will occur later
(after 00Z) at those sites, and likely no worse than MVFR at INT.

Outlook: Low overcast and areas of light rain or drizzle will
scatter and lift to VFR from sw to ne Thursday morning to early
afternoon. Thereafter, a pair of strong shortwave troughs aloft and
related surface cold fronts will cross central NC Thursday afternoon
and Thursday night, the former of which will likely be accompanied
by a band of showers and sub-VFR conditions. Breezy to windy
conditions will follow for Fri into Fri night.

&&

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

&&

$$
SYNOPSIS...MWS
NEAR TERM...WSS
SHORT TERM...Haines
LONG TERM...Haines
AVIATION...MWS