-- Discussion containing changed information from previous version are highlighted. --
569
FXUS62 KRAH 260805
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
405 AM EDT Sun May 26 2024

.SYNOPSIS...
High pressure ridging will build into the area Sunday. A cold front
will approach Sunday night and move through the region Monday night.
Dry high pressure will settle into the region toward the middle of
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
As of 400 AM Sunday...

...Unseasonably warm and humid airmass today will bring a level 1
risk for damaging wind gusts during the late afternoon into the
evening hours...

Skies have cleared over central NC and has lead to pockets of fog to
develop along riverbanks and where the heaviest precipitation fell
the day prior. Point soundings show this saturated layer is quite
shallow and should dissipate rather quickly after daybreak. Weak
shortwave ridging will shift over central NC and the Southeast this
morning in between the departing wave over the Atlantic and a
deepening shortwave into the Upper Midwest through the afternoon. A
moist and unstable airmass will remain in place today characterized
by dew points in the mid/upper 60s and MLCAPE of 500-1500 J/kg.
Drier air aloft deposited by the shortwave ridging and fairly
uniform southerly surface flow today should result in less spatial
coverage in diurnal showers/storms compared to Sat. Best chances
will likely be over the Northeast Piedmont into the Coastal Plain
where MLCAPE (1000-1500 J/kg) and 0-3km CAPE (50-150 J/kg) will be
maximized and may be able to overcome the dry air aloft through
local clustering along a common cold pool. Weak flow through 500mb
will favor mostly a pulse storm mode.

Attention then turns upstream to a developing MCS over the mid-
Mississippi Valley early this morning. Hi-Res guidance shows a
favorable environment for MCS maintenance this morning into the
evening hours as it rides along the CAPE gradient into the lower
Ohio Valley. As it traverses the NC mountains during the late
afternoon into the evening hours, the environment becomes less
favorable, but still characterized by 1000-1500 SBCAPE and steep low-
level lapse rates around 9 C/km that will bring a risk for mainly
strong to severe wind gusts, especially to the Triad. As this system
moves ESE through central NC uncertain begins to increase towards
the Triangle and into the Sandhills and Coastal Plain and will
depend on the maturity of this system as MLCIN begins to increase. A
mature, well formed system will be able to overcome the weak
boundary layer stability and tap into increased 500mb flow and
MUCAPE around 1500 J/kg to persist and bring a damaging wind threat
through midnight (represented by 06z HRRR and 00z HRW-ARW). The
alternate scenario would feature a less mature and broken line of
storms as it progresses through the Triad that will struggle persist
after sunset and show a weakening trend as it progresses through the
Triangle and points south and east (represented by the 00z HRW-NSSL
and 06 NamNest). Observational trends will need to be watched
through the afternoon to determine the most likely scenario.

Overnight lows under variable cloudiness and light stirring will be
well above normal and settle in the upper 60s to low 70s.
-- End Changed Discussion --

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 315 AM Sunday...

Still tough to get a handle on convection timing. We`ll likely see
the remnant wave/MCV and clouds from today`s storms over the Mid
Miss Valley and W Ohio Valley passing into the Carolinas and Mid
Atlantic during the morning hours. While this early timing and
convective debris clouds are not ideal for destabilization, we`re
still likely to have moderate MLCAPE with morning low and mid level
lapse rates of 6.5-7 C/km and improving low- and mid-level flow to
25-30 kts and 40-55 kts respectively, amid high PWs of 1.5-1.8",
exceeding the 90th percentile. The more favorable kinematics appear
to shift E into the Coastal Plain and E NC during the afternoon,
with a stark downturn in mid level flow late in the day and a dip in
CAPE that may be due to the morning showers and isolated storms.
There remains some potential for temporal and spatial overlap of the
more ideal thermodynamic environment with the better wind fields and
incoming MCVs, which would support a decent severe storm threat, but
such an alignment is far from guaranteed. The latest NCAR neural net
guidance presents two rather muted windows for potential severe
threat, one in the mid morning and the second in the mid afternoon
to early evening associated with the incoming longwave trough axis
and ahead of the incoming surface cold front, although the possible
morning cloudiness and convection may reduce this late-day threat.
Will maintain 20-30% pops in the morning, increasing to good chance
to likely in the afternoon, highest NW near the cooler mid levels
associated with the incoming longwave trough. These higher pops
should shift into our E sections after 00z, then exiting all but the
far SE overnight. Thicknesses are expected to be 10-20 m above
normal, supporting highs in the mid 80s to around 90. Lows in the
mid 60s NW, where some lower dewpoints will begin to work in just
behind the front, ranging to around 70 in the SE. -GIH

&&

.LONG TERM /TUESDAY THROUGH SATURDAY/...
As of 145 AM Sunday...

Dry weather is expected during this period with generally low
humidity and seasonable to slightly below normal temps. The longwave
trough axis will still be to our W Tue, and while there may be minor
waves shifting through SC and SE NC, much of the deeper moisture
will have pushed E of our area or even offshore. Will keep a slight
chance of an afternoon shower or storm in our far SE, as large scale
models show the front slowing or lingering over our SE sections
where surface temps and dewpoints are apt to be elevated. A dry NW
flow will keep the column dry and stable Tue night through Wed,
although the notably cooler air will still be held up W of the
mountains until a secondary reinforcing dry cold front drops SE
through our area late Wed through Wed night. Behind this front,
dewpoints will drop even more, bottoming out in the 40s to low 50s
Thu/Fri as surface high pressure sourced from central Canada builds
in from the NW and N. By Sat, both temps and dewpoints will start to
rebound as the mid-upper longwave trough shifts out over the NW
Atlantic and amplified mid level ridging builds in from the west.
Low level thicknesses will rebound as the surface high starts to
shift off the Mid Atlantic coast, and thus temps will edge closer to
normal Sat. And with the onset of southeasterly low level flow and
an uptick in PWs, a few late-day showers may pop up across the S and
W, and will include just slight chances there. Temps will still be
near to slightly above normal Tue and near normal Wed, before
dropping to a few degrees below normal Thu/Fri with low humidity and
lots of sunshine. Near normal readings should return Sat. -GIH

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
As of 220 AM Sunday...

Cirrus clouds are rapidly exiting to the east with SKC overspreading
central NC. Patchy fog may still be possible near all TAF sites, but
with lowest confidence at GSO, INT, and RDU where crossover temps in
the low/mid 50s may be too low to see prevailing fog. FAY has
reported variable fog for a few hours and the 06z TAFs continued
this slow trend down to low-end IFR towards daybreak despite briefly
bouncing back to VFR around 0530z. Lingering shallow fog will
quickly dissipate through 12z with afternoon cumulus filling in
areawide with airmass showers/storms possible 17z-22z. Hi-Res
guidance tracks an MCS through the Mid MS Valley early this morning
and into the Carolinas through the evening hours. Latest forecast
attempts to capture the best time to see restrictions associated
with this system with prevailing VCTS based on latest CAM guidance
and with TEMPOs where confidence is highest (40-50% chances at GSO
and INT).

Looking beyond 06z Mon: A vigorous line of showers and thunderstorms
over the Ohio and Tennessee Valley early Mon morning will weaken as
it traverses the mountains and likely bring scattered to numerous
showers/storms through central NC during the day on Mon. Additional
showers/storms will be possible as the first of several cold fronts
moves through central NC Mon night. Dry and VFR conditions will
prevail through Thurs.

&&

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

&&

$$
SYNOPSIS...Kren
NEAR TERM...Swiggett
SHORT TERM...Hartfield
LONG TERM...Hartfield
AVIATION...Swiggett