595
FXUS62 KRAH 180632
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
230 AM EDT Wed Sep 18 2024

.SYNOPSIS...
A large upper level low over the western Carolinas will slowly drift
east then northeast, tracking along the Mid Atlantic and Northeast
coast through Friday. A trailing upper level trough will persist
just off the East Coast through the weekend, as an upper level high
pressure ridge builds over the Gulf States. This ridge will shift
east into the Southeast states early next week.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 820 PM Tuesday...

The training band of showers and storms over northern portions of
the coastal plain and Piedmont is starting to fizzle out, but not
before producing a narrow corridor of 1 to 3 inches and
nuisance/minor flooding. Some shower activity may linger into the
overnight hours towards the Triad as the occluded low and mid-level
forcing begins to wobble back east. Otherwise, expect widespread low
clouds to re-develop across the area. Additionally, fog, potentially
dense, may develop along and north of the front, generally across
the northern Piedmont and coastal plain. Overnight lows in the lower
to mid 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
As of 315 PM Tuesday...

The remnants of PTC 8 and the associated upper low will be over
upstate SC Wednesday morning, with the axis of best deep moisture
shifting north into VA. An occluded front over the Piedmont today
will remain mostly unchanged. The upper trough is forecast to weaken
and open up as it, along with the weak surface reflection, drift
east during the day, with the trough axis likely to be somewhere
over the coastal plain by Thursday morning. Scattered showers will
continue to rotate around the low and will increase in coverage as
some weak instability develops during the day, with the potential
for best coverage near a occluded front/convergence axis that
lingers across the Piedmont.  The best instability is forecast to
spread north from SC into the southern coastal plain during the
afternoon and that is where the depth and coverage of showers or
isolated storms could be best.  The overall deep layer wind field
will be weak and any storms are not expected to be very strong. Deep
moisture is forecast to increase again from the south, as the upper
low/trough begins to slide east, so showers will be heavy, and there
are some indications from the HREF PMM that some showers could
produce up to 2 inches of rain, although they will be isolated and
not likely to cause much of a flooding concern on the whole.

Consistent with the area of better destabilization, the best heating
will be across the south and east as clouds are more likely to
linger in the north and west.  There is good model agreement on
highs ranging from the mid 70s to mid 80s.

The showers will likely continue to the overnight hours in the
vicinity of the upper low and a convergence axis across the northern
portions of the area. Lows will be in the mid to upper 60s with some
decent signals in the SREF for fog north of the boundary as well.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
As of 230 AM Wednesday...

This looks to be a largely dry period, with slightly below normal
temps favored most days.

The mid-upper level low over the Mid Atlantic coast early Fri will
continue a drift to the NNE over the coastal Northeast into the
weekend, as a trailing mid-upper trough along the East Coast shifts
very slowly offshore. This will keep us in a dry NW steering flow
through Sun as an anticyclone over SE TX builds slowly eastward into
the Mid South and across the Gulf States. At the surface,
corresponding low pressure over the far NW Atlantic off the
Northeast and New England coast will periodically reload but
maintain a slow E drift, as its trailing backdoor fronts extend SW
then W through the Carolinas and Mid Atlantic region. Deterministic
models vary with backdoor front placement and movement; the GFS and
Canadian, for example, show a weak front to our S and W early Fri,
before washing it out by Sat and allowing temps to moderate, only to
have them knocked back down below normal by a second backdoor front
passage Sun night and a cool wedging high nosing down through
central NC through early next week. The ECMWF takes this second
backdoor front southward through NC earlier (Sat night). Weak low
level mass convergence along any backdoor front is possible, and
despite generally low PW and a lack of moisture availability from
850 mb up through the mid levels, such convergence could prompt a
few shallow showers. But overall, there`s a lack of opportunity for
deep moisture return through at least Mon, so will carry nothing
more than isolated pops at most, an outcome in line with the latest
LREF and other ensemble suites. By Tue, there are indications that
the mid level ridge over the Gulf States will shift E into the
Southeast, nudged by deep mid-upper troughing over central Canada
through the US Plains states, and this onset of WSW flow aloft could
support rising chances for convection over the NC mountains into the
foothills and perhaps our far NW Piedmont. This timing could shift,
however, so will keep Tue pops aob climo for now. Will keep temps
near to slightly below normal through Sun, before lowering them a
few more degrees for Mon/Tue. -GIH

&&

.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 215 AM Wednesday...

While showers have exited central NC, a decaying low pressure system
currently centered over the western Carolinas will continue to bring
anomalous low-level moisture. This will result in widespread sub-VFR
ceilings and visibilities overnight across the north (including INT,
GSO, RDU and RWI) where an associated front is also set up. Ceilings
there have already dropped to LIFR, with IFR and LIFR visibilities
also being reported from fog. Farther south around FAY, clearing has
taken place, but this could still aid in some patchy fog formation
later tonight. Conditions will gradually improve in the morning and
early afternoon, but some MVFR ceilings should linger for much of
the day across the north. A period of scattering to VFR will be
possible, especially at RDU and RWI. VFR is expected across the
south including FAY. Sub-VFR ceilings and visibilities will again
overspread the region from north to south in the evening. Scattered
showers and isolated storms will also be possible in the afternoon
and evening.

Outlook: An unsettled period will continue through Thursday with
areas of overnight and early morning stratus and a risk of some
afternoon showers and possibly a storm. Aviation conditions will
generally improve for the weekend.

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...CBL
SHORT TERM...BLS
LONG TERM...Hartfield
AVIATION...Danco/Luchetti