-- Discussion containing changed information from previous version are highlighted. --
195
FXUS62 KRAH 201421
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1021 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 AND TONIGHT/...
-- Changed Discussion --
As of 1020 AM Friday...

No major changes with this morning update. There is still a bit of
lingering fog in the southwest Piedmont as of 930 AM, but that is
expected to dissipate in the next hour or so as the boundary layer
continues to mix out. The 12Z upper air analyses show the upper
trough situated along the East Coast, with the anticyclone over srn
TX, ridging newd through the central Plains and mid MS Valley. The
atmosphere remains saturated over central NC at H7 an H85. At the
surface, high pressure encompasses the mid-Atlantic and Carolinas,
while a low sits off the northern mid-Atlantic coast.

A mid/upper level s/w is swinging through central NC this morning
and should exit to the east this afternoon. Some drier H7 air is
expected to advect into the area from the northeast, ahead of a
trailing mid-level disturbance sliding sewd through the northern
Coastal Plain and northeast Piedmont late this aft/eve. It is this
feature that could help some showers develop. Exactly where the
mainly isolated to scattered showers will develop remains somewhat
uncertain, but for now the best chances will likely be along the H7
moisture gradient (over the NC Piedmont) as the mid-level
disturbance swings through the area. Some of the hi-res guidance
still shows about 500 J/Kg of SBCAPE across central NC this aft/eve,
so cannot rule out an isolated thunderstorm. Highs ranging from
around 80 degrees north to mid 80s south. -KC

From the previous discussion (as of 235 AM Friday): 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
-- End Changed Discussion --

&&

.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/...
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.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
As of 645 AM Friday...

Patches of MVFR to IFR vsbys in fog persist at this hour across
central NC, mainly east of the Triad terminals, a result of warm
moist air and very light winds near the ground. Due to the patchy
nature of this shallow fog, vsbys at any given location have been
highly variable, wavering among LIFR/IFR, MVFR, and VFR within an
hour, and this should persist until around 13z-14z. Areas of mid
clouds moving through north and central areas have helped to keep
the most dense fog from becoming too widespread, but pockets of low
vsbys and cigs remain possible through mid morning N and S of these
clouds. A gradual dispersion and mixing out of fog/stratus will
result in a trend to VFR conditions by 16z, persisting through early
tonight. Another round of patchy early-morning fog and stratus
producing sub-VFR conditions is possible 07z-12z Sat morning.
Isolated showers are possible later today, but the greatest chance
will be in the SW, S and W of the primary terminals. Surface winds
will remain light (under 10 kt) mainly from the NE or ENE through
tonight.

Looking beyond 12z Sat, patchy sub-VFR conditions may persist
through 14z Sat morning, 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...KC/Hartfield
SHORT TERM...Hartfield
LONG TERM...Danco
AVIATION...Hartfield