382
FXUS62 KRAH 170755
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
355 AM EDT Fri May 17 2024

.SYNOPSIS...
An upper level disturbance will move across the area this afternoon
and tonight. An upper level trough will slowly move eastward through
the mid-Atlantic and Carolinas on Saturday and Sunday before moving
off the coast on Monday. High pressure will build into the area for
the first part of the work week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 325 AM Friday...

* Increasing chances of showers and a few thunderstorms this
  afternoon and especially tonight.

The latest surface analysis shows a cold front extending from the
Great Lakes southwest into the MO Valley with an area of low
pressure over the lower MS Valley with an attendant west to east
frontal zone. Weak high pressure extends south from the New England
area into the western Piedmont of VA and the Carolinas. The air mass
across central NC is rather stable but with dew points mainly in the
lower 60s with a few mid 60s in the Coastal Plain. Regional radar
shows a few stubborn showers drifting southwest across the northeast
Piedmont and the northern/central Coastal Plain. These showers
appear to be associated with a weak perturbation aloft noted on the
1.5 PVU surface.

Expect any lingering showers/sprinkles early this morning will
dissipate by daybreak with some patchy mid clouds across the Coastal
Plain and a few areas of fog. Otherwise, bright sunshine this
morning will give way to increasing high and mid clouds that will
spread east and northeast across the area later this morning and
afternoon. Higher resolution convection allowing models appear to be
resolving the perturbed mid and upper level flow that generates a
couple of waves of ascent that will produce scattered to numerous
showers and few storms this afternoon and tonight. The great
precipitation coverage is likely to be across the southern and
western Piedmont late this afternoon and early evening with a second
round of more numerous showers and storms overnight toward daybreak
Saturday morning. Instability will be rather limited, likely reduced
by lacking mid level lapse rates, and will only include a slight
chance/chance of storms late this afternoon into tonight. Highs
today will range near or perhaps a touch warmer than on Thursday.
Highs should range in the upper 70s to lower 80s with a few highs in
the mid 80s across the southern tier. Mile and muggy lows tonight
will range in the mid and upper 60s. -Blaes



&&

.SHORT TERM /SATURDAY THROUGH SATURDAY NIGHT/...
As of 345 AM Friday...

* Lots of uncertainty with the evolution of convection on Saturday
  and Saturday night after a lull on Saturday morning.
* The chance of convection increase on Saturday afternoon,
  especially across the south where there`s an increased risk of
  strong to severe storms.

The mid and upper air pattern on Saturday and Saturday night is
complicated with multiple shortwave troughs embedded in an elongated
trough axis that extends along and a little west of the Appalachian
mountains on Saturday morning. The trough axis will shift east on
Saturday with the embedded disturbances spreading across the mid-
Atlantic and Carolinas with the trough axis extending northeast to
southwest across VA and the western Carolinas by Sunday morning.
Guidance is highlighting the potential for a weak wave of low
pressure to develop across the Deep South, ahead the trough, and
move across southern NC on Saturday afternoon evening. This will
provide a focus for convection and introduce a surface boundary
separating slightly cooler and more stable air across the northern
Piedmont and northern Coastal Plain with a more humid/unstable air
mass to the south near the SC border. Further complicating the
forecast is the potential for deep convection to spread across the
Deep south on Saturday which may complicate and disrupt the
downstream environment. The southwesterly flow across the Carolinas
strengthens ahead of the approaching trough on Saturday afternoon
and evening with 0-6km bulk shear values of 30-40kts possible across
southeast areas. Accordingly, SPC has introduced a level 2 slight
risk across southern/southeastern NC which just skims into our
southeastern Counties. The primary severe weather risk will be
damaging winds but given the location of the frontal zone and
enhanced shear near a surface wave, will need to closely monitor the
location of the low and front which could increase the tornado
potential. With a decent amount of forcing for ascent in the area
thanks to the upper trough, scattered convection may continue well
into Saturday night.

Highs on Saturday will range from the lower 70s near the VA border
to the lower 80s across the south. Expect a good deal of cloudiness,
but if more intervals of sunshine occur, highs could jump into the
mid 80s across the south which would enhance instability and add to
the threat of strong to severe storms. Lows on Saturday night will
range from around 58 across the north to 64 across the south. -Blaes

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
As of 208 PM Thursday...

Saturday and Sunday: Slightly better model agreement this weekend
wrt the s/w. Aloft, the sub-tropical ridge just off the East Coast
will be gradually suppressed and shunted eastward as a potent s/w
progresses generally eastward through the central Appalachians,
lower mid-Atlantic and Carolinas this weekend. The GFS and ECMWF
solutions have trended toward one another, increasing overall
forecast confidence. The character of the wave appears to be more of
an open trough than a closed low at the mid/upper levels as it moves
through the Appalachians and mid-Atlantic Sat/Sat night, possibly
closing off as it slides slowly sewd through the Carolinas Sun/Sun
night. At the surface, there is still some variability between the
model guidance, but generally expect a warm front to lift through
the area early Sat, while an area of low pressure should track
through the area Sat aft/eve (although details are uncertain).
Expect the surface low to be off the Carolina coast by Sun, with a
backdoor cold front moving swd into the area late Sat night/early
Sun. The question wrt this feature is the timing and strength of the
subsequent wedge front that may develop over NW NC on the backside
of the low for Sun/Sun night. The result is continued forecast
uncertainty, especially wrt temperatures Sun/Sun night.

Temperatures: Highs Sun ranging from mid 70s along the VA border to
mid 80s in the SE. Lows generally ranging from upper 50s north to
mid 60s south. Trickier for Sun as there is some bust potential, but
for now expect highs ranging from mid 60s north to mid 70s south.

Outlooks: All of central NC is included in a Marginal Risk for
severe storms and a Marginal Risk for excessive rainfall on Saturday.

Off the GFS forecast soundings: Sat, MUCAPE ranging from a few
hundred J/Kg in the NW to around 600 J/Kg in the SE, while bulk
shear should generally be in the 20-30 kt range, possibly a bit
higher early. PWATS of 1.5 to 1.8 inches NW and 1.6 to around 1.9
inches in the south and east Sat aft/eve. For Sun: With the expected
wedge airmass across much of the northern portions of central NC,
expect largely stable conditions within that airmass, while across
the SE portions of the area MUCAPE could again peak around 600 J/Kg,
although bulk shear values will generally be around 20 kts. PWATS of
1.5 to 1.7 generally expected.


Monday onward: The upper low may linger over/just off the Carolina
coast Mon through Tue night, then open into a trough and lift newd
away from the area Wed/Thu. The sub-topical ridge will sit over the
MS Valley through Tue, then gradually shift eastward, ridging
through the mid-Atlantic through Tue night. A couple of northern
stream shortwaves will track eastward through the Great Lakes from
late Mon night through Wed, largely staying north of the area, while
a southern stream wave may move into/through the region Wed
night/Thu. The next potential for showers/storms across the area
will be with this wave Wed night/Thu. Expect temperatures to
moderate through mid-week.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
As of 235 AM Thursday...

Generally fair weather with VFR conditions is expected across much
central NC this morning with deteriorating aviation conditions during
the afternoon and especially evening hours. Note that some very
localized showers will move across the northern Piedmont and the
northern Coastal Plain early this morning which could produce a
brief VSBY reduction near KRDU and KRWI. In addition, some very
patchy fog is possible through around daybreak across the Coastal
Plain and eastern Piedmont which may impact the KRWI/KRDU and even
KFAY terminals with some marginal MVFR VSBYS.

The fog and lingering showers should quickly dissipate just after
daybreak. VFR conditions with increasing mid and high clouds are
expected this morning into this afternoon. An approaching upper
level disturbance will spread scattered showers and a few
thunderstorms northeast across the area from the west and southwest
during the afternoon and tonight. Precipitation coverage will
increase with MVFR CIGS and some VSBY restrictions becoming
increasingly likely from west to east tonight with some IFR CIGS
possible across the western Piedmont late tonight.

Looking beyond 06Z Saturday, an unsettled weather pattern is
expected with period of showers and some thunderstorms. Coverage
will likely be the greatest tonight into early Saturday and again
late Saturday afternoon and evening with a lingering risk on Sunday.
Areas of sub VFR conditions are likely during this period. Improving
conditions and mainly VFR conditions are expected Monday into
Tuesday. -Blaes

&&

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

&&

$$

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