121
FXUS62 KRAH 261525
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1122 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/...
As of 1122 AM Sunday...

...Marginal risk of severe thunderstorms this afternoon and tonight.

Weak shortwave ridging and sunny skies have been observed over
central NC this morning. A rather moist and increasingly unstable
air mass is expected this afternoon and evening. It will be
characterized by dew points in the mid 60s NW ranging into the lower
70s SE and MLCAPES of 1000-1500 J/kg increasing to nearly 2000 J/kg
by late afternoon as highs reach the upper 80s to lower 90s. Little
more than isolated (20 percent chance) of showers/thunderstorms
expected this afternoon until attention then turns upstream to a
developing MCS over KY/IN 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 into the central Appalachians
and possibly western or NW North Carolina, with some development of
scattered strong-severe thunderstorms out ahead of this system by
400 - 500 PM over the Appalachians, and toward 600 PM for Winston-
Salem. As it traverses the NC mountains during the late afternoon
into the evening hours, the environment becomes less favorable with
time, but still characterized by 1000-1500 SBCAPE and steep low-
level lapse rates around 9 C/km that would bring a risk for mainly
strong to severe wind gusts, especially to the Triad.

As this system moves ESE through central NC, uncertainty increases
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.

&&

.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 /12Z SUNDAY THROUGH THURSDAY/...
As of 710 AM Sunday...

Patchy shallow fog will quickly dissipate early this morning.
Coverage of early afternoon pop-up showers/storms continues to show
more isolated in nature with probabilities less than 20% through the
afternoon of impacts at any terminals with best chance at RWI. A
developing MCS over the Mid-MS Valley will motor through the lower
Ohio Valley and Tennesse Valley through the mid afternoon and
traverse the NC mountains during the late afternoon into the evening
hours. The Triad terminals have the best chance (40-50%) chance to
see restrictions from this system, but exact impacts remain
uncertain until this system fully develops. Strong to severe wind
gusts, heavy rain, and lightning will certainly be possible. Farther
east, model guidance remains split on whether the MCS will fall
apart or continue as a mature MCS through central NC. A few hours of
VCTS at RDU, FAY, and RWI has been used to cover this threat but
further refinement will be required through the afternoon.

Looking beyond 06z Mon: Another 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...Badgett
SHORT TERM...Hartfield
LONG TERM...Hartfield
AVIATION...Swiggett