National Weather Service National Headquarters

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 231943
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
343 PM EDT Sun Sep 23 2018

.SYNOPSIS...
A backdoor cold front will sag slowly southward through the area
today. Behind the front, cool high pressure will extend southward
through central North Carolina through Tuesday. Weak low pressure
will track northward over coastal North Carolina Tuesday night into
Wednesday.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
As of 255 PM Sunday...

The low level stable pool remains over the N Piedmont at this hour,
topped with high thin clouds streaking across N/W NC. But as the
last few CAM runs have foretold, the low clouds have begun to break
up, and recent GOES channel 2 vis imagery reveals stable wave clouds
in this region, with convective clouds along its S/E edge. We`re
finally starting to see some shallow showers along the differential
heating zone at the edge of the wedge front, from around Scotland
Neck SW near RWI and TTA. This is along a narrow zone of marginal
CAPE and around 25 kts of effective shear, and as these should both
be maintained for a few more hours, we should continue to see
scattered showers and perhaps an isolated storm or two through the
rest of the afternoon. Loss of heating should result in a
diminishing of the convection, and a backing of weak steering flow
to a SSE direction should prompt a drift of any remaining isolated
convection into the NW Piedmont through the rest of the evening.
Weak moist upglide that has abated for much of the day is expected
to resume this evening, resulting in the low clouds filling back in
tonight, with the thickest/lowest clouds across the climatologically-
favored Piedmont, an area that may also see patchy drizzle
overnight. Expect lows mostly in the low-mid 60s, perhaps some upper
60s SE. -GIH

&&

.SHORT TERM /MONDAY AND MONDAY NIGHT/...
As of 340 PM Sunday...

The offshore-centered mid level anticyclone will build briefly W
over the eastern Carolinas Mon, while the surface ridge centered and
drifting E over the Canadian Maritimes noses SSW through central NC.
Strengthening onshore low level flow from the SE will result in
increasing moist upglide atop the weakening stable wedge, and recent
model runs generally indicate patchy light rain breaking out over E
NC (where upglide is initially strongest) before spreading inland
into central NC through the day. Will start the day mostly cloudy to
cloudy areawide, with chance pops east early, spreading NW through
the area through the day, before decreasing and diminishing Mon
night. Cloudiness will hold firm Mon night given the weak flow and
moist and somewhat stable low levels overnight. Expect highs from
around 70 NW to the low 80s SE, followed by lows in the mid to upper
60s. -GIH

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
As of 345 PM Sunday...

Tuesday morning the CAD will begin to loose its grip over the
Triad as a wave pulls northeast around a subtropical ridge
anchored off the east coast. As this occurs, the wedge will
start to fall apart and loose cohesion. High temperatures
Tuesday will quickly rebound with 850 mb temperatures
approaching 18 degrees C towards the Coastal Plain.
Simultaneously,an axis of PV will be located over the
Mountains of western North Carolina. This again will make for a
bimodal distribution in QPF Tuesday afternoon into Wednesday
morning. The chance of precipitation looks to move towards a
minimum Wednesday morning as the wave and aforementioned PV
exits the area. This should provide a brief period of
subsidence.

Wednesday evening, a long wave trough axis will center over the
central United States with an upper level disturbance pulling
northeast. The wave will quickly pull northeast though towards
Lake Ontario. The main batch of PV will miss NC, but PWATs will
climb towards 2.00" along with an approaching upper level jet
streak. This will help to increase the chance of precipitation
Wednesday evening and keep it going through Friday. The initial
shortwave mentioned above will cause a cold front to stall and
washout across the area late Wednesday. The ECMWF actually holds
onto the front as a wedge signal late Thursday, while the GFS
(and CMC) are much weaker with the front.

A secondary shortwave traversing northern Ontario late Thursday
into early Friday will be stronger than the initial wave, but
further north. This second wave will be followed by another
surface cold front. The GFS is slightly quicker and stronger
with the front compared to the ECMWF. Cooler and drier air will
exist with this front, but is nothing compared to what is was
advertised as in previous model runs. The secondary shortwave
now looks to eject far to northeast with the rex block off the
west coast of the U.S finally dislodging allowing for low
pressure to deepen. These dropping heights off the west coast of
the United States will only aide in the demise of the long wave
trough. This means that even behind the cold front temperatures
will still be near to above normal.

&&

.AVIATION /19Z SUNDAY THROUGH FRIDAY/...
As of 1215 PM Sunday...

At INT/GSO/RDU: IFR cigs within the cool stable air north of the
backdoor front will continue to gradually lift to MVFR this
afternoon, with holes breaking through the overcast skies. A short
period of VFR conditions is possible, mainly 20z-00z, with a small
chance of a shower near RDU. But as we approach sunset, low clouds
are expected to fill back in quickly, with a return to IFR cigs and
to MVFR to IFR vsbys (fog) shortly after 02z. These sub-VFR
conditions should hold through at least mid morning Mon. Cigs will
slowly lift to MVFR between 14z and 18z (the end of the TAF valid
period.

At RWI/FAY: VFR conditions will hold at FAY, while MVFR cigs at RWI
should improve to VFR by 20z. These two locations will also see a
chance of a shower this afternoon and early evening, until around
00z. Conditions should then begin to drop to MVFR then IFR by 05z at
RWI and by 07z at FAY, where they will remain until cigs/vsbys
slowly improve to VFR after 15z.

Looking beyond 18z Mon: Slow improvement will continue Mon
afternoon, with MVFR to low-end VFR lasting through the rest of the
day. A return to IFR is expected Mon night areawide, followed by
another slow improvement to VFR Tue, with a chance of showers and
storms, greatest at RWI/FAY. Clouds and the shower/storm coverage
will increase for Wed/Thu/Fri as a front approaches from the NW and
stalls over the region. -GIH

&&

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

&&

$$
SYNOPSIS...Hartfield
NEAR TERM...Hartfield
SHORT TERM...Hartfield
LONG TERM...Haines
AVIATION...Hartfield