290
FXUS62 KRAH 231102
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
702 AM EDT Thu May 23 2024

.SYNOPSIS...
A warm and humid air mass over our region, combined with the passage
of a series of upper level disturbances over the area, will produce
unsettled weather through Monday, with daily chances of showers and
storms. A drier air mass will arrive by the middle of next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 400 AM Thursday...

Regional radar imagery shows an MCS traversing through the  lower MS
Valley with multiple embedded convectively induced MCVs. These
localized areas of ascent will track generally ENE along the
cyclonic side of the mid-level ridge and should initiate convection
along the NC mountains where a lee-trough will help focus
showers/storms with 500-1500 J/kg of SBCAPE over the Piedmont into
the Sandhills during the afternoon/evening. Slight strengthening of
the 500mb flow will support 30-40 kts of bulk shear and will favor
some organization of stronger storms. The big question mark today is
the subtle forcing from the MCVs and inconsistencies in timing any
MCVS that emerge from convection upstream over the lower OH Valley.
This is leading to wildly different solutions from run-to-run,
making a deterministic forecast difficult.

An ensemble approach from the HREF suggests initially cellular
convection over the mountains and foothills transitions into a messy
convective cluster as it approaches the Piedmont as deep shear
vectors align parallel to the lee trough and eventual outflow and
cold pool from merging clusters. Any discrete cells will bring the
risk of hail and locally damaging winds while congealing clusters
will primary bring a straight-line wind threat. However, an overall
moist thermodynamic profile and only modest instability may struggle
to produce severe wind gusts, but localized strong to severe gusts
within organized cold pool clustered convection can not be ruled
out. Afternoon temperatures will be similar to yesterday with
mid/upper 80s, although isolated locations of around 90 will be
possible especially in the Coastal Plain and portions of the
Piedmont and Sandhills.

Showers and storms will likely weaken as they transition eastward
with less instability to work with and diurnally unfavorable timing
based on current forecast. Dependent on the rainfall footprint,
patchy fog may be possible late tonight into Fri morning, but given
the already myriad of uncertainties with the evolution of
afternoon/evening convection, confidence is low on fog potential. No
major airmass change is expected behind the afternoon showers/storms
and lows will remain in the mid/upper 60s.

&&

.SHORT TERM /FRIDAY AND FRIDAY NIGHT/...
As of 145 AM Thursday...

Tough to have a lot of confidence in the forecast for Friday, given
that the timing and evolution of convection in our area will be
greatly dependent on what happens today in NC (including any
lingering outflows or differential heating boundaries) and upstream
in the S Plains into the lower Miss Valley, as any resulting MCVs
from this area (riding on long-fetch SW flow from off Baja
California) could help drive our Friday storm chances. This
uncertainty is reflected in the later hours of the CAMs, which show
little agreement.

The most likely scenario involves some combination of the larger
scale mid level trough now over the Desert Southwest, a residual MCV
from today`s S Plains convection, and perhaps a weak boundary left
over our region from today`s storms, all working with high PW in the
90th percentile, marginal to mdt SBCAPE, and warm surface temps and
dewpoints in the warm sector within weak lee surface troughing to
promote scattered to numerous multicell storms from mid to late
afternoon through the evening. Such storms would be most likely
across our S and E, as some models suggest that an earlier mid level
wave at 700 mb pushing off the Mid Atlantic coast in the early
afternoon would introduce some brief WNW flow and drying across our
N and W. Then the GFS/ECMWF depict a trailing shortwave trough
(perhaps an MCV) moving into the NC mountains Fri evening/night,
which, if it occurs, could support additional late-day mountain
convection poised to push into the NC Piedmont overnight. Will start
with slight shower chances through lunchtime, then ramp up pops to
good chance everywhere except likely far S and SE, where any
lingering boundary from today is apt to settle. Will keep chance
pops going overnight for showers and isolated storm, but again,
confidence in all of this is low, considering how much is predicated
on today`s activity here and well upstream. Under partly to mostly
cloudy skies, and starting the day with thicknesses just a bit above
normal, expect highs in the 80s (low NW ranging to upper SE), around
5 degrees above normal, followed by muggy lows in the mid 60s to
lower 70s, 8-10 degrees above normal. -GIH

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
As of 310 AM Thursday...

Daily chances for showers and storms are expected Sat through Mon,
with pops decreasing by Tue/Wed with a shift in the longwave
pattern.

The aforementioned Fri night shortwave trough is expected to be over
central or eastern VA/NC Sat morning. If this feature is a bit
slower, then the cooler mid levels and DVPA may prompt high coverage
of storms with heating across our east. If this wave is faster, then
that will bring rearward shortwave ridging into our area Sat,
reducing our pops. With our area firmly in warm/moist advection, PW
still above normal, and surface troughing still in place over the
area, will lean on the high side of climo pops, esp E, with 40% NW
ranging to 55-60% SE Sat. Expect a brief downturn in pops late Sat
night through much of Sun as the shortwave ridging passes overhead
coincident with a dip in PW, but with upstream convection in the
Plains and Miss Valley continuing to eject perturbations through the
Mid Atlantic region with no real pattern change for us at the
surface, we should see convection chances quickly return, and will
retain chance pops Sun afternoon and evening. We start to see signs
of a longwave pattern change starting Memorial Day, as a deep
northern stream low/trough moves into the Midwest/Great Lakes. This
will set up faster and more cyclonic mid level flow with steepening
mid level lapse rates, suggesting high pops, esp late in the day and
into Mon night. Will have good chance to likely pops, highest Mon
afternoon/evening. As longwave troughing sets up over E NOAM,
Tue/Wed should be fairly dry with below-climo chances for showers
and storms.

Thicknesses will hold above normal Sat, favoring highs in the 80s to
near 90, then highs will reach peaks of mid 80s to lower 90s Sun and
Mon, pushing heat indices well into the 90s all but the far N. By
Tue, as the upper trough axis and associated cold front move
through, temps should drop back close to normal. -GIH

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
As of 700 AM Thursday...

VFR conditions continue this morning with a low predictability for
showers and storms this afternoon through the evening. The forecast
has trended slower and with less coverage in the afternoon compared
to 00z guidance with a better chance for a cluster of showers and
isolated storms moving through the area overnight. The 12z TAFs have
trended towards this threat given the sparse guidance that has
trickled in since 06z, but further updates will likely be needed as
observations and model trends continue to narrow in on the wide
variety of forecast solutions. Behind the showers, patchy fog and
low stratus may be possible near FAY tonight into Fri morning, but
given inconsistencies in prior convection this threat also includes
low predictability.

Looking ahead: Primarily diurnally driven showers/storms will be
possible at all terminals Fri through Mon.

&&

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

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Swiggett
SHORT TERM...Hartfield
LONG TERM...Hartfield
AVIATION...Swiggett/KC