626
FXUS62 KRAH 251053 RRA
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
653 AM EDT Sat May 25 2024

.SYNOPSIS...
Above normal temperatures along with humid and unsettled weather
will continue through Memorial Day. A cold front will move through
Monday night, bringing drier, more seasonable, and less humid
conditions Tuesday through Friday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 355 AM Saturday...

Regional satellite and radar imagery show three separate
disturbances rotating through the lower Ohio Valley and into the
southern Mid-Atlantic, an MCV near Charlotte, a weak shortwave in
southeastern KY, and finally a shortwave and likely a convectively
induced MCV in southern IN into western KY. Each of these will most
likely be the focus for showers/storms in central NC through
tonight. Hi-Res guidance is understandably struggling to resolve
these features and is leading to inconsistencies from run-to-run and
a low confidence forecast.

Based on an ensemble approach, a moist and unstable airmass will be
in place over most of the area during the afternoon with 1000-2000
J/kg of MLCAPE expected. A lee trough over western NC may be the
primary focus for showers/storms with 20-30 kts of bulk shear
resulting in some storm organization, most likely congealed clusters
along a common cold pool. Convection would track ESE along the
greatest instability gradient through the southern Piedmont into the
Sandhills. Low-level lapse rates will become steep as surface
temperatures rise into the upper 80s to 90 and may pose a strong to
severe wind gust threat ahead of any organized clusters. Over the
Piedmont into the Coastal Plain, weaker instability (~1000 J/kg) and
bulk shear (10-20 kts) will likely result in isolated pulse type
storm mode.

Skies will clear behind the departing showers/storms with weak
pressure gradient over central NC overnight. This will favor another
night of patchy fog with areas of fog possible in locations that
receive the heaviest rainfall. Lows will mostly fall into the mid
60s with low 60s possible in the typical cool spots in the Piedmont.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 315 AM Saturday...

The messy and uncertain convection potential continues through Sun,
although the latest guidance (with an eye to what`s happening now
upstream) is in fairly good agreement in focusing our chances across
our W and S later in the day. Mid level shortwave troughing will
have moved off the VA/NC coast Sat night, leaving us beneath
shortwave ridging Sun morning. Widespread strong to severe
convection should be ongoing across MO/SE IA/S IL, generating an MCV
that will likely track ENE through Sun, mostly skirting to our NW
but still perhaps scraping through our W and N late in the day. Low
level jetting does ramp up after 21z and into the nighttime hours
esp across our W, although the most impressive LLJ will be further
WNW over the Ohio Valley, beneath ideally juxtaposed upper jets that
will be generating vigorous upper divergence there. It appears that
our greatest coverage of convection will then be in the evening and
overnight across our W and S, as the upstream convection and
resultant MCVs spread E into the S Appalachians and perhaps into our
area. But as this activity heads ESE, coverage should dwindle across
our E (and esp NE) where the mid level heights will still be a bit
higher with a later arrival after nightfall suggesting a lower CAPE
and higher SBCINH environment. Our surface air mass will remain warm
and humid, and PWs will hold above normal, even over the 75th or
90th percentile in some areas, so a stray shower or storm can`t be
ruled out anywhere starting in the late morning, but will place the
higher pops Sun from very late in the afternoon through much of the
night. The risk of severe storms will be fairly modest across the E
but better over our W and westward through the NC mountains, where
mid level flow will be improving to 30-40 kts late in the day versus
15-25 kts in E NC. Mid level lapse rates will also be smaller in the
E versus W NC. The somewhat dry low levels on forecast soundings
suggest more of a wind threat late Sun/Sun night in our SW,
supported by CSU ML output. Expect variable cloudy skies with warm
temps in the upper 80s to around 90. Muggy lows in the upper 60s to
lower 70s. -GIH

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 155 AM Saturday...

High rain chances Memorial Day into the night will yield to an
imminent pattern change to drier and less humid conditions starting
Tue and lasting through the week.

The details in timing and location of convection Mon/Mon night will
greatly depend on what culminates prior in situ and upstream, given
the outsized influence of various mid level perturbations (mostly
MCVs) and surface boundaries (differential heating discontinuities,
new and old outflows, and sea breezes) in focusing showers and
storms and guiding their tracks and evolution. And lingering debris
clouds from Sun/Sun night convection here and immediately upstream
may affect our heating and potential buoyancy Mon. What is of higher
certainty is the continued presence of a warm and humid air mass, a
deeply moist column, and increasing winds at all levels ahead of an
approaching surface cold front and a profound longwave trough/low
sweeping through the Midwest and Great Lakes region Mon. This will
create favorable conditions for scattered to numerous showers and
storms with improving organization late day heading into Mon night.
The LREF members have SBCAPE peaking at 1000-2500 J/kg (25th/75th)
over much of central NC, with mid level flow strengthening to 40-50
kts amid PW of 1.5-1.75". Incoming dynamic forcing for ascent in the
form of mid level DPVA (in particular with a late-day shortwave
trough swinging through W and N NC) and upper divergence should also
boost storm intensity and organization. Will have pops rising to
good chance to categorical, highest NW in the afternoon and in the
Coastal Plain in the evening, trending down overnight with cold
front passage. Highs in the upper 80s-lower 90s. With the front
passing through Mon night, lows should be in the lower 60s NW but
still mid 60s to near 70 S and E.

Mostly dry weather will follow for the rest of this period. 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 50s and perhaps
even some 40s Thu/Fri as surface high pressure sourced from central
Canada builds in from the NW and N. Temps will still be near to
slightly above normal Tue/Wed, before dropping to a few degrees
below normal Thu/Fri with low humidity and lots of sunshine. -GIH

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 650 AM Saturday...

Periods of shallow MVFR fog around RWI should quickly dissipate
through 12z. The forecast remains on track for loosely organized
showers and storms in the vicinity of the Triad terminals (GSO/INT)
this afternoon that will continue to track to the ESE through the
late afternoon and evening hours. Timing and eastward extent of the
showers/storms related to RDU and FAY remains uncertain, but FAY may
have the better chance to see storms within its vicinity this
evening. These storms will bring the risk for strong and erratic
wind gusts as well as heavy rain and reduced vsby. Airmass
showers/storms will be possible near RDU and RWI, but expected
coverage will mostly likely be isolated enough to not include in the
12z TAFs at this time.

Looking ahead: Primarily diurnally driven showers/storms will be
possible at all terminals through Mon, with the best chances Mon
aft/eve ahead of a cold front, which should move through the area
Mon night.

&&

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

&&

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