-- Discussion containing changed information from previous version are highlighted. --
920
FXUS62 KRAH 200753
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
353 AM 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 build in from
Texas across the Gulf and Southeast states through early next week.

&&

.NEAR TERM /TODAY THROUGH TONIGHT/...
As of 235 AM Friday...

Patchy ground fog will be an issue through mid morning, then expect
a largely dry day for most, but with isolated afternoon showers
primarily over the W and S Piedmont into the Sandhills.

A diffuse MSLP pattern persists over NC early this morning, and the
combination of this very weak near-surface flow fostering nocturnal
stabilization along with a damp ground has prompted patchy fog
formation, much of it shallow and pooled in low spots. Areas of mid
clouds have hindered prime radiational cooling over our far W and E
areas, but as these mid clouds continue to drift southward through
this morning, most places should see at least some fog, some of it
dense. Will monitor for the need for a dense fog advisory.

Otherwise, once the fog lifts and disperses by mid to late morning,
skies should be partly cloudy, but various models and ensemble
systems differ on rain chances. Deterministic models such as the GFS
and ECMWF paint a wide swath of precip across all but our far NE
this afternoon into early evening, with peaks in amounts over the SW
Piedmont, a solution mostly corroborated by the NAM and latest RAP
runs. But ensemble output such as the NBM and HREF show only a few
fleeting isolated showers today into tonight. Observational data
does show support for at least some weak forcing for ascent today,
with weak perturbations seen on current GOES layer WV imagery over W
PA on pace to drop through VA into N NC by this evening, and daytime
heating with surface dewpoints in the 60s and minor moisture flux
from a damp ground could result in a few hundred J/kg of SBCAPE
later today. Will include a period of isolated showers across the W
and S Piedmont into the Sandhills later today, with the dry mid
levels likely to curb most deep convection that could generate
lightning. Highs from the upper 70s to mid 80s. Any showers should
peter out and shift to our S early this evening, leaving dry
conditions overnight, however another round of patchy fog and low
stratus is probable late tonight, following persistence with little
change in antecedent conditions and surface wind. Lows generally 60
to 65. -GIH

&&

.SHORT TERM /SATURDAY AND SATURDAY NIGHT/...
As of 315 AM Friday...

Confidence is increasing in scattered showers and perhaps a few
storms across the N and W Piedmont and far NE late Sat. A prominent
shortwave seen on WV imagery over the Upper Midwest is on track to
round the top of the amplified ridge centered over TX and covering
much of the central CONUS through tonight, before diving SE through
the Mid Atlantic region late Sat and Sat night. While the timing of
this DPVA may not take full advantage of the daytime heating and
resulting destabilization this far SE, we should see an uptick in
mid level flow to support some deeper convection esp over the
mountains to our NW, and this activity may spill SE into our NW and
far N sections very late in the day and through the evening. Most
deterministic models and ensemble systems support this, with
isolated to scattered coverage across our NW and far N late
afternoon through the evening, and this is where we`ll have 15%-30%
pops, mainly from 21z-06z but with perhaps an isolated shower or two
lingering in the far NE overnight. With dry weather through much of
the Sat daytime hours, temps should reach slightly above normal
highs around 80 to the mid 80s, as thicknesses are projected to be 5-
10 m above normal. Lows in the low-mid 60s Sat night. -GIH

&&

.LONG TERM /SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
As of 350 AM Friday...

Weak surface high pressure will ridge down the Mid-Atlantic on
Sunday as low pressure several hundred miles east of the Mid-
Atlantic coast drifts slowly south. Looking aloft, central NC will
be under the influence of dry NW flow between the troughing in the
Atlantic and ridging building into the Deep South and TN Valley.
However, a weak disturbance in the flow may generate a few showers
in the east on Sunday afternoon and evening, which is backed up by
the latest deterministic runs of the GFS and ECMWF along with some
of their ensembles. However, any showers should be light and shallow
given the dry air aloft. Temperatures on Sunday will only get to
upper-70s to lower-80s in the far NE (where the cooler wedge from
the surface high will begin to reach), but elsewhere they should be
mid-to-upper-80s. Sunday night`s lows will be in the lower-to-mid-
60s.

Shortwave ridging will be in place across central NC on Monday,
between the mid/upper low off the coast and the next shortwave
trough moving east from the Central Plains. Despite the ridging,
some moisture may spill over into our area with increased clouds,
and can`t rule out an isolated shower or storm in the far NW.
Temperatures should be slightly cooler on Monday with the surface
high nosing down, so forecast highs are in the upper-70s to lower-
80s.

This trend of increasing shower/storm chances continues on Tuesday
(chance POPs NW) and Wednesday (chance POPs areawide) as the
shortwave and associated surface low pivot NE into the Great Lakes,
while the surface ridging over the Mid-Atlantic weakens and lifts
back NE. The cold front to the south of the low will approach from
the west, but guidance greatly differs on its speed. The ECMWF
brings it through central NC late Wednesday (drying us out for
Thursday) while the GFS keeps it hung up over the Mountains. Enough
ECMWF ensembles disagree with the deterministic run to warrant low
chance POPs continuing on Thursday. A slight warming trend will
bring highs into the lower-to-mid-80s on Wednesday, while confidence
in Thursday`s temperatures is low as it will depend on frontal
timing.
-- End Changed Discussion --

&&

.AVIATION /06Z FRIDAY THROUGH TUESDAY/...
As of 100 AM Friday...

The chance for MVFR-IFR fog remain high early this morning (mainly
07z-14z), due to warm moist air and very light winds near the
ground. Areas of mid clouds currently cover the far W Piedmont
(including GSO and esp INT) as well as our NE sections, which is
helping to keep fog from becoming too widespread so far, however as
these mid clouds continue to push southward and break up, widespread
dense fog and areas of low cigs in stratus are likely. There are no
strong indicators favoring one particular terminal over another for
dense fog formation, but most guidance indicates the best chances
are E of the Triad, including RDU/RWI/FAY which have all seen some
rain in the last 24 hours to further moisten the ground. A gradual
dispersion and mixing out of fog/stratus will result in a trend to
VFR conditions by 16z, persisting through early tonight. Isolated
showers are possible later today, but overall the vast majority of
the area will stay dry. Surface winds will remain light (under 10
kt) mainly from the NE or ENE through tonight.

Looking beyond 06z Sat, another round of areas of early-morning fog
and stratus producing sub-VFR conditions is possible 08z-14z Sat
morning across central NC terminals, otherwise VFR conditions are
favored to dominate through early Sun night. A backdoor front will
drop through NC Sun night as high pressure noses in from the north,
bring another chance of sub-VFR conditions early Mon morning and
again early Tue morning. Mostly dry weather will persist, however,
through Tue. -GIH

&&

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

&&

$$

SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...Danco
AVIATION...Hartfield