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412
FXUS62 KRAH 211829
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
230 PM EDT Sat Sep 21 2024

.SYNOPSIS...
An upper level disturbance will track southeast through the Mid
Atlantic region tonight. A back-door cold front will move south
through the area late Sunday followed by surface high pressure
extending south into the area through much of the upcoming work
week.

&&

.NEAR TERM /TONIGHT/...
As of 203 PM Saturday...

A line of scattered showers and thunderstorms is progged by all of
the HREF members to develop to our north this evening then drift S
and SE across our CWA between 04-10Z tonight... all in response to
the weak short wave trough that is currently crossing the Ohio
Valley, which is forecast to move ESE across the Mid Atlantic region
tonight and move off the coast by Sunday morning.  In the meantime,
we`ll see intervals of sct-bkn shallow cu the remainder of the
daytime hours today, esp west of US-1 where currently the best
moisture and instability is located... then high clouds moving in
this evening out ahead of the upstream shower/tstm activity. Then
during the hours right before daybreak, there could be a couple
hours of patchy fog, esp locations the see the greatest coverage of
showers/tstms overnight. Lows tonight in the low-mid 60s.

&&

.SHORT TERM /SUNDAY AND SUNDAY NIGHT/...
As of 115 PM Saturday...

Aloft, the sub-tropical ridge will progress eastward through the
srn/ctl Appalachians and into the Carolinas through Sun night.
Central NC should be under nwly flow on the northeast periphery of
the ridge. At the surface, a low will continue sliding sewd through
central NC Sun morn/aft. A backdoor cold front should slide south
through the area Sun aft/eve, with high pressure ridging in behind
it. There could be some lingering showers across the east Sun
morning. Additional showers/storms could slide swd through the
Coastal Plain/far ern Piedmont Sun eve/night as the backdoor front
slides southward through the area. There could be about a 10 degree
spread in highs from SW to NE due to the front, around 90 degrees SW
to low 80s NE. Lows could drop to around 60 degrees in the northeast
Sun night, with generally mid 60s expected elsewhere.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
-- Changed Discussion --
As of 230 PM Saturday...

* Near to slightly above normal temperatures into midweek, followed
  by seasonal to slightly below average late week and weekend

* Shower and storm chances highest Tue into Thu

* Forecast confidence decreases mid to late week as ensemble systems
  continue to differ on the overall synoptic pattern and possible
  tropical influences

We will start the week with ridging building into the area at mid-
levels from the north and northeastern Gulf. High pressure will
build into the area from the Eastern Seaboard and Canada. Models
still show a lingering backdoor front to our southwest in northern
SC, though it appears models have trended further south with its
location. As such, rain/storm chances are lessened Mon aftn/eve, but
still cannot rule out a 20-30 percent chance over the western and
southern Piedmont. Temperatures will be near normal in upper 70s to
low 80s.

Ridging will continue into midweek, though we should get increasing
influence from a trough over the MS/OH valleys and Great Lakes late
Tue through early Thu. Model and ensemble solutions start to diverge
on how the trough evolves as it moves east, but there does appear to
be a general consensus that a cold front will try to move through
sometime Thu morning. It`s still unclear whether it will actually
move through or stall out and linger NW of us. Ahead of that front,
shower and storm chances should increase (30-60 percent), primarily
in the late Tue through Wed night period. Temperatures should rise
above normal ahead of the front to above average in the low to mid
80s.

Probabilistic and ensemble solutions continue to vary widely in the
Thu to Sat timeframe with respect to the synoptic pattern. Some
ensemble cluster solutions indicate troughing over the MS valley and
ridging off the western Atlantic (aka latest GFS/CMC), which would
favor warmer highs and help draw northward any disturbance in the
Gulf later in the week. Where it tracks though is widely varied.
Other solutions show troughing nearby with the aforementioned cold
front, keeping rain chances elevated. And still a third solution
shows a rex/omega ridge pattern near the OH valley and troughing on
either side, which could favor drier conditions to start but also
advect any tropical system in the Gulf over the weekend. This is
seen in the prior 00z ECMWF. Speaking of the Gulf, NHC now has a 60-
percent chance of tropical development late next week over the south-
central Gulf. Where the system would move is highly dependent on the
pattern discussed above, which is too uncertain, but certainly bears
watching, given a wide range of potential impacts. As a result, have
kept rain chances low Thu to Sat, with temperatures near to slightly
below normal in the upper 70s to near 80.
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&&

.AVIATION /18Z SATURDAY THROUGH THURSDAY/...
As of 203 PM Saturday...

Through 18Z Sunday:  Currently seeing VFR conditions across central
NC attm, with the exception of very local bkn shallow cu around 3k
ft agl invof the Triad region.  Otherwise, a cluster of showers and
storms are expected to move across much of central NC overnight,
first across the Triad including KINT/KGSO as early as 04Z, then
across KRDU about 06-08Z, then KRWI/KFAY between 08-10Z. These
showers/tstm could briefly result in MVFR cigs/vsby with any of the
heavier showers.  Then between 09-12Z, patchy MVFR fog may develop,
esp where the heavier rain falls.  VFR conditions will return after
12Z Sunday.

After 18Z Sunday: Mainly VFR conditions expected each day, with the
exception of sub-VFR fog/stratus each morning. There is a chance for
mainly afternoon/evening showers/tstms each day, which could also
briefly reduce flt conditions at times.

&&

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

&&

$$

SYNOPSIS...np
NEAR TERM...np
SHORT TERM...KC
LONG TERM...Kren
AVIATION...np