812
FXUS62 KRAH 051904
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
300 PM EDT Sun May 5 2024

.SYNOPSIS...
A stationary front across the western Piedmont will dissipate this
evening. An upper-level disturbance across western NC this afternoon
will exit the area to the northeast this evening. Another upper-
level disturbance will approach the mid-Atlantic on Monday and exit
the region on Tuesday. High pressure will extend into the during the
mid week before a cold front approaches late in the work week.
&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 300 PM Sunday...

* Scattered to numerous showers and storms associated with an MCV
  will move northeast across the Piedmont through early afternoon
  and the Coastal Plain into the early evening.
* A more stable air mass in the Triad should result in just a little
  patchy rain or a few showers through the afternoon.

The latest water vapor satellite imagery and regional radar imagery
shows a well defined vortex/MCV that is tied to convection that
moved across northeast GA/Western SC last evening. This feature is
located across the western Piedmont of NC, a little west of KRDU
this afternoon and is driving multiple clusters of showers and
storms across the eastern Piedmont and Coastal Plain. Across the
eastern Piedmont, Sandhills and Coastal Plain, a warm and humid air
mass with dew points in the mid to upper 60s and a southeast wind is
in place. The air mass across the western Piedmont and Triad is more
stable with lingering low clouds in place. The air mass has become
weakly to moderately unstable across the southeast with MLCAPE
values a little in excess of 500 J/Kg.

As the MCV continues to move northeast, the scattered to numerous
showers and storms will continue to lift northeast and shift east
over the next several hours. As the afternoon wares on the focus for
convection will shift into the Coastal Plain. Given the modest mid
level lapse rates and weak to possibly moderately unstable airmass,
a few enhanced wind gusts up to 35 mph are possible. Further west,
just a few showers may move across the western Piedmont through the
late afternoon.

Upper level forcing wanes this evening and overnight with some weak
mid level ridging extending across the area. The axis of deepest
moisture slips east slightly but PW values remain near 150% of
normal overnight. Can`t rule out an isolated shower overnight and
there is a signal for convection that may develop in far western NC
to hold together and move into the western Piedmont as it fades late
this evening. Otherwise, clouds will thicken up again tonight and it
will be muggy. Overnight lows will range in the lower to mid 60s.
-Blaes

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
As of 210 PM Sunday...

Aloft, the sub-tropical ridge will try to briefly build over the
Southeast US on Mon, but will then be pushed eastward again as the
s/w to the west moves eastward across the Appalachians and into the
mid-Atlantic late Mon/Mon night. This s/w trough may become slightly
negatively tilted as it swings through the region. At the surface,
high pressure will sit over Bermuda, ridging swwd into the Southeast
US through Mon night. A quasi-stationary frontal zone will extend
from the Northeast US, wswwd through the OH Valley and mid-MS
Valley, remaining north of the area through Mon night. Expect sly to
swly flow over central NC Mon/Mon night, resulting in continued
advection of warm, moist air into the area.

Precipitation/Convection: With the continued feed of warm, moist air
into the area, MUCAPE of 800-1500 J/Kg is forecast by both the NAM
and GFS across the area during the day, while effective shear is
forecast to be about 15-20 kts. After a brief drop in PWATs tonight,
they should climb back into the 1.5-1.75 inch range on Mon. All of
the ingredients will be present for storms to develop, contingent on
forcing. The best forcing for ascent will be with the s/w aloft,
however the models vary with the timing of that feature. The hi-res
model guidance from 12Z suggests showers and storms may develop over
the Piedmont during the afternoon, then move eastward through the
evening. A secondary round of showers and storms moving across the
mountains Mon eve could continue eastward through the area Mon
night. For now, central NC remains in general thunder from the SPC
and the hi-res guidance varies on the coverage and intensity of
convection. Given all of the above, cannot rule out an isolated
strong/severe storm should all the ingredients come together at the
right time Mon aft/eve, before loss of heating and nocturnal
stabilization commences.

Temperatures: Expect largely broken/overcast skies through Mon
night. Highs should range from the upper 70s NW to mid 80s SE, with
lows mainly in the low to mid 60s Mon night.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
As of 1211 PM Sunday...

Upper pattern for the extended: A short-wave will exit to our east
early Tuesday, behind which mid-level ridging will build back over
the southeast through late Wednesday.  The ridge will de-amplify as
a strong vort max digs into the Midwest Thursday, eventually
ejecting eastward through the northeast US. This feature will induce
increasingly swly flow aloft over central NC Friday into Saturday.

Temperatures: Hot and humid conditions will persist Tuesday through
Thursday under the anomalous mid-level ridge.  The NBM still
continues to highlight high probabilities for >90 degrees for
locations south and east of Raleigh both Wednesday and Thursday (The
GEFS, EPS, and GEPS are less enthused, but generally depict a
similar geographic area with highest probabilities (10-30%)). Given
dew points will peak in the upper 60s/lower 70s, heat indices will
likely pop up into the mid 90s both Wednesday and Thursday
afternoons. Thus, make sure to take frequent breaks in the shade and
hydrate if spending a lot of time outdoors these days.

Temps will "cool" off a bit Friday and into the weekend as the
aforementioned upper vort max/trough dips into the southeast. Highs
in the mid 80s are currently expected Friday, followed by mid to
upper 70s on Saturday. However, these may need to be modified some
as we get closer and guidance comes into better agreement/confidence
increases.

Precipitation: POPs will be lower Tuesday and Wednesday under
general ridging aloft (and some nwly flow in the lower levels should
lower PWAT a bit). However, can`t rule out some isolated/scattered
diurnally driven showers/storms along any differential heating
boundaries including late day sea breeze migration into our area.
Some guidance depicts some energy aloft trickling through our area
late Wednesday which could maybe generate a bit more activity.
However, will keep POPs capped at low chance for now.

As we progress into the Thursday through Saturday timeframe, there
is some uncertainty wrt to the evolution of the aforementioned
strong vort max/trough and an associated cold front. However, the
general consensus among ensembles/deterministic output is that this
upper feature does look strong enough to possibly induce an airmass
change for our area later this weekend (i.e. a stronger cold front
actually making it`s way to the coast). As such, showers and storms
are likely ahead of and along the cold front as it moves through.
While we`ll need a bit more updated model guidance to get into
specifics, it does appear at this point that some severe storms will
be possible Thursday and Friday as guidance suggests an uptick in
mid-level lapse rates and bulk-layer shear in this time frame.
Again, a bit too far out for specifics, but we`ll continue to
monitor as we get closer to later next week.

&&

.AVIATION /18Z SUNDAY THROUGH FRIDAY/...
As of 215 PM Sunday...

An upper level disturbance moving northeast across western NC this
afternoon will trigger scattered to numerous showers and some
thunderstorms across much of the area. Showers and embedded
thunderstorms will move across the KFAY and KRDU terminals through
around 21Z with brief period of IFR VSBYS and perhaps CIGS along
with wind gusts of around 25kts. The unsettled weather with showers
and storms will persist longer at KRWI, until around 23Z.
Further west, in a more stable airmass and behind the
disturbance, spotty showers are possible at the KINT/KGSO
terminals through around 22Z but no thunderstorms are expected.

Most of the widespread showers and deep convection should have
exited the area by 00Z with mainly VFR to MVFR conditions with some
CIG restrictions early this evening. The overnight should largely be
dry although an isolated shower is possible, with the best chance
across the west. Widespread IFR and MVFR restrictions will redevelop
late this evening in stratus and fog. LIFR condition are likely late
tonight in the northern and western Piedmont, especially the KINT
and KGSO terminals. Conditions should slowly improve on Monday
morning with more showers and storms possible on Monday afternoon.

Outlook: Scattered to numerous afternoon and evening showers and
storms are expected on Monday. Rain chances decrease for Tuesday and
Wednesday with just a limited threat of an afternoon/evening shower
or storm before rain chances increase on Thursday. With a moist
airmass in place, areas of fog and stratus are possible on
Tuesday morning with reduced chances during the mid week. -Blaes

&&

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

&&

$$

SYNOPSIS...Blaes
NEAR TERM...Blaes
SHORT TERM...KCP
LONG TERM...Luchetti
AVIATION...Blaes