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118
FXUS62 KRAH 170644
AFDRAH

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

.SYNOPSIS...
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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.
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&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1000 PM Thursday...

Regional satellite imagery shows a deeply occluded low pressure
system spinning just off the Delmarva Peninsula with an area of
isolated very light showers and altocumulus persisting from
Louisburg, NC into south-central Virginia. The showers are being
forced by a convergence in 925-850mb with weak pocket of elevated
instability around 500 J/kg. Point soundings suggest a gradual
weakening of the instability through after midnight and supporting
isolated and very light showers through ~07z before dissipating all
together.

Patchy fog will be possible tonight, but density and areal extent
has been inconsistent in latest NWP. A back door front and/or
pressure trough stemming from the occluded low over the Atlantic
will sag through eastern and central VA into northwestern NC tonight
into early Fri morning. Lower theta-e airmass behind the front
should prevent fog potential over the northeast. Elsewhere, rich low-
level moisture (mean mixing ratio of 10.5 to 11 g/kg from 00z
GSO/MHX respectively), little to no moisture/temperature advection
in the low-levels, and most locations already becoming calm as of
01z obs, radiational cooling to or below the crossover temperature
(lowest dewpoint during peak heating) will be the locations where
patchy fog will be most probable (rural areas of the Piedmont,
Sandhills, into the central/southern Coastal Plain). Lows tonight
were lowered in outlying areas given pockets of favorable
radiational cooling. Lows will range from the upper 50s to low 60s
with isolated mid 50s possible in the typical cool spots in the
Piedmont.

&&

.SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/...
As of 145 PM Thursday...

Increasing rain chances again late Friday and Friday night.

The day will begin with low pressure over the Plains, with dry
weather and partly to mostly clear skies over central North
Carolina. However, the rain shield will extend well east of the low
pressure and showers should begin to move into the area during the
afternoon. A lot of model disagreement still remains for how great
the coverage will be both Friday afternoon and Friday night. Some
models are suggesting that showers will move in with widespread
coverage, others are suggesting that there will be an initial band
of rain that moves in during the afternoon/evening, then a good
portion of the night will be dry. Went with the NBM for much of the
daytime, then tempered the NBM pops Friday night with the NAMDNG,
which is not as aggressive. However, this still keeps likely pops
for most locations west of I-95 Friday night. Have gone with a
chance of thunderstorms during the afternoon/evening then a slight
chance of thunderstorms overnight. Most locations will be a few
degrees warmer on Friday than today despite additional cloud cover
with warm advection, and also warmer Friday night because of warm
advection and the additional cloud cover.

&&

.LONG TERM /SATURDAY 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 /06Z FRIDAY THROUGH TUESDAY/...
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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
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&&

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

&&

$$
SYNOPSIS...Blaes
NEAR TERM...Swiggett
SHORT TERM...Green
LONG TERM...KC
AVIATION...Blaes