-- Discussion containing changed information from previous version are highlighted. --
064
FXUS62 KRAH 202357
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
751 PM EDT Fri Sep 20 2024

.SYNOPSIS...
An upper level trough along the East Coast will shift slowly
eastward and offshore through Saturday morning, as a weak surface
high pressure ridge extends from New England down through the
central Carolinas. An upper level disturbance will track southeast
through the Mid Atlantic region late Saturday through Saturday
night. An upper level high pressure ridge will then begin to build
in from Texas across the Gulf and Southeast states through early
next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 310 PM Friday...

As the upper trough situated along the East Coast continues to shift
eastward, the ridge extending enewd from the anticyclone over srn TX
will begin ridging into the region. At the surface, high pressure
continues to encompass the mid-Atlantic and Carolinas, while a low
sits off the northern mid-Atlantic coast. Isolated to scattered
showers will persist into the early evening, then taper off with
loss of daytime heating later in the evening. The SPC mesoanalysis
page has roughly 500-1000 J/Kg of MLCAPE across the Piedmont as of 3
PM, so still cannot rule out an isolated thunderstorm, but lightning
has yet to materialize. Highs should be topping out in the low to
mid 80s. The surface ridge may strengthen from the northeast
tonight, with some slightly cooler air potentially filtering in.
However, under NE flow expect moisture off the Atlantic to also
advect into the area. The weather should be dry overnight, however
patchy fog and low stratus is expected again late tonight into early
Sat. Lows tonight should range from upper 50s NE to mid 60s south.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
As of 400 PM Friday...

Nwly flow aloft will result across cntl NC through the weekend,
between a mid-level anticyclone that will drift from s-cntl TX to
the cntl Gulf coast and a shortwave trough that will amplify from
the lwr Great Lakes to along and offshore the nrn middle Atlantic
coast Sat-Sat night. Glancing height falls of 10-20 m/12 hr and
seasonably strong, ~30-40 kt mid-level flow will occur over the srn
middle Atlantic late Sat-Sat night. That shortwave trough will then
be absorbed by a preceding cyclone that will wobble from near the
coast of srn New England today to near and north of Bermuda through
early next week.

At the surface, a narrow ridge initially extending across ern VA/NC
will drift to the coast and allow for the development of light, sly
flow across cntl and wrn NC Sat afternoon. That sly flow will be
directed into both an Appalachian-lee trough over wrn NC/VA and a
weak low and accompanying frontal zone that will extend from the OH
Valley to nrn VA. An associated lee low and closely-following
backdoor cold front will then drift across cntl and Southside VA Sat
night and through cntl NC Sun afternoon-evening. High pressure will
follow and extend from Atlantic Canada swwd and across the Northeast
and middle Atlantic Sun night-early next week.

The light sly, low-level flow will result in continued above average
temperatures to finish the summer, with highs mostly in the middle
80s and lows mostly middle 60s. Moisture, surface and deep, will
maximize along and east of the lee trough over wrn NC, where the
airmass will become moderately unstable with diurnal heating.
Although the greatest concentration of storms should result from the
VA Blue Ridge to cntl-nrn VA, along the intersection of the front
and lee trough, isolated cells will be possible into the nrn/nwrn NC
Piedmont Sat afternoon-evening. While nocturnal stabilization should
cause those storms to diminish through the evening, a weak warm air
advection regime above the nocturnally-stabilizing boundary layer
will support a continued slight chance of showers/storms over the ne
Piedmont and nrn-cntl Coastal Plain overnight.

Sun should again be unseasonably warm to hot ahead of the backdoor
front, with pre-frontal temperatures between 85-90 likely, ranging
to slightly less warm lwr 80s where the frontal passage may occur
prior to peak heating toward HNZ and IXA. The backdoor front may
also be accompanied by scattered showers/storms Sun afternoon-
evening, followed by patchy light rain from post-frontal, low
overcast late Sun night-Mon morning.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As of 235 PM Friday...

Near to slightly above normal temperatures will start the period
early next week. Forecast confidence decreases after Wed with
ensemble solutions not in agreement on the pattern. As such,
temperatures are less certain but currently projected to be near to
slightly below normal in the upper 70s to low 80s. While rain
chances are possible Mon through Fri, highest confidence for showers
exist Tue into early Thu.

Ridging builds in from the TN valley Mon, while at the surface the
passage of a backdoor front will settle somewhere along the far
southern Piedmont and along the SC border. High pressure will nose
down into the region from Maine. Highs will be lower from the weak
cold advection and some daytime stratus. Expecting mid/upper 70s NE
to low 80s SW. We cannot rule out an isolated shower/storm in our
far southern and southwest zones along the stalled boundary, as well
as along the far NW Piedmont tied to some weak upslope.

Come Tue and Wed, guidance shows a system across the MS valley
trying to bring a cold front into the region. Ensemble solutions
start to diverge, however, regarding the frontal passage, if at all,
depending on the strength of the ridge in the far NE Gulf and the
trough over the Great Lakes. Solutions that bring the front through
show a passage late Wed night to early Thu. Have retained 20-40
percent chances of isolated to scattered storms, highest presently
for Wed, but confidence remains on the low end.

By mid to late week, ensemble solutions continue to diverge and
overall forecast confidence is low. Some ensemble solutions bring NW
flow aloft with a cold frontal passage, favoring drier conditions
and slightly below normal temperatures, while other solutions keep a
trough to our west in the MS valley, favoring warmer highs. This
pattern would favor higher storm chances in the late-week period as
it could pull deeper moisture into the area from the Gulf. NHC is
tracking the potential development of a tropical depression (50
percent chance of formation) over the northwestern Caribbean Sea and
southern GOM late next week. If something were to indeed form, its
energy could get pulled into the Deep South by the aforementioned
trough, depending on the pattern. Given the large model spread, PoPs
Thu/Fri are only 20-30 percent.

&&

.AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 751 PM Friday...

Primarily VFR conditions are expected the next few hours as a few
isolated showers wane this evening. Dry conditions are expected
overnight. However, fog and stratus are likely to develop across
central NC overnight and especially between ~08 and 13Z Saturday
morning. As such, will continue the mention of IFR/LIFR ceilings and
visibilities over this temporal range at all terminals. It does
appear that KRWI may have the best chance for dense fog, but patchy
fog will be possible at all terminals.

Outlook: VFR conditions should generally prevail through mid-week,
with the exception of sub-VFR fog/stratus each morning. Light rain
or showers will be possible each day but those details remain fairly
uncertain at this time.
-- End Changed Discussion --

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...KC
SHORT TERM...MWS
LONG TERM...Kren
AVIATION...Luchetti/KC