Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS62 KRAH 290807
Area Forecast Discussion
National Weather Service Raleigh NC
407 AM EDT Wed Mar 29 2017
Weak high pressure will move over central NC today and remain in
control through Thursday before low pressure brings unsettled
weather to the area for Friday and Friday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 405 AM Wednesday...
Fairly quiet out there this morning as a frontal system exits the
CWA to the southeast evident in dewpoints as KCTZ is still carrying
59 degrees with upper 40s and lower 50s dewpoints to the northeast.
There is a chance for some fog, mainly across the northeastern
counties and extreme east over the next several hours. Otherwise the
main concern will be for MVFR ceilings again in the northeast as
northeasterly flow takes over and brings moisture in from the
Atlantic. Central NC will be under the influence of a very remote
surface high centered over northern Ontario. Expect some low clouds
for much of the day but could see some breaks of sun by afternoon.
No precipitation is expected. High temperatures in the low 70s
across the northeast, but climbing into the upper 70s in the
southwestern counties. Lows in the upper 40s to mid 50s. Some chance
for some early morning stratus in the Triad going into Thursday
.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
As of 405 AM Wednesday...
Thursday will be quiet during the day as a meso-high develops over
the Delmarva Peninsula which will throw temperatures into question a
bit for Thursday afternoon. if flow remains southeasterly over the
area, we should see temps near 60 degrees across the north with
highs closer to 70s in the south. If flow remains more northeasterly
temps could come in quite a bit cooler, especially across the north.
By Thursday night, the first waves of precipitation associated with
an approaching low pressure system will begin to overspread at least
the western portions of the CWA, and perhaps everywhere by 12z
Friday. Diurnal timing should keep most of this activity limited to
convective showers as instability is non-existent. That being said,
model soundings show every strong veering with height and wind
profiles suggest bulk shear of 50 knots or so with a large heaping
pile of helicity in the lowest levels of the atmosphere. Will
certainly keep an eye on these details as they evolve. Lows Thursday
night mainly in the 50s.
.LONG TERM /Friday through Tuesday/...
As of 220 AM Wednesday...
Fri/Fri night: Stormy weather for central NC, as a mid level low
will move over the Ohio Valley and central Appalachians to off the
Mid Atlantic coast, a path which models agree fairly closely on,
although the ECMWF is much weaker with this low than the GFS/NAM. A
band of vorticity trailing this low down through the Mid South and
Gulf early Fri will swing ENE with a negative tilt through the
central Carolinas Fri morning, accompanying enhanced upper
divergence and high PW nearing 1.5". Models including the SREF, NAM,
GFS/GEFS, Canadian, and MPAS are unanimous with widespread
showers/storms Fri morning into the afternoon, so will have
categorical precip chances, trending down a bit from the SW late in
the day and into Fri evening as the trough axis and DPVA pivot to
our ENE, bringing partial drying in the mid/upper levels. While the
mid and low level lapse rates are generally under 7 C/km and the
strongest forcing for ascent is on track to move through the area
prior to peak heating, the GFS spreads surface CAPE of 800-1200 J/kg
through cntrl/E NC Fri afternoon, buoyed by a surge of high surface
dewpoints of 55-60F, and kinematics are quite strong with 40-50 kts
of deep layer shear and 150+ m2/s2 of 0-1 km helicity, so we may
still see a few strong to severe storms Fri, generating both large
hail and damaging winds, as well as a tornado risk, especially near
the northward-retreating surface frontal zone possessing strongly
curved low level hodographs. Precip chances should be ending over
the NE CWA late Fri night as the mid level low/trough starts heading
off the Delmarva coast, with a trailing front working eastward
through the NW Piedmont of NC. Expect highs in the upper 60s/lower
70s followed by lows in the low-mid 50s.
Sat through Sun night: Fairly quiet weather this weekend. The
surface front is likely to settle near the NC/SC border, with no
strong push in either direction, as initial weak NW mid level flow
behind the exiting trough is slowly supplanted by a mid level ridge
axis shifting eastward over the Southeast by late Sun. There`s no
polar air behind this front, as a somewhat mild high crosses the
Great Lakes region and Northeast. But models do suggest that the
northeasterly low level flow into NC will draw in enough low level
moisture within the low level stable layer to generate nighttime and
morning stratus Sat night/Sun morning and again Sun night, with
partial mixing-out during the daytime Sun for partly to mostly sunny
skies. Model thicknesses are generally slightly above normal Sat and
near normal Sun, suggesting highs in the low-mid 70s Sat, lows 47-52
Sat night, and highs Sun 67-73. Lows Sun night in the upper 40s to
lower 50s, with fair skies NE and increasing clouds SW as the
surface high moves off the Mid Atlantic coast, yielding gradually
strengthening overrunning flow from the SE.
Mon through Tue: More stormy weather as yet another potent wave
tracks from the S Plains E then NE through the lower Miss Valley,
dampening slightly as it traverses the Mid South and Central
Appalachians. Model timing differences of as much as 12 hours make
it impossible to pin down the details at this range, but it appears
likely that we`ll see good coverage of showers and storms from Mon
afternoon well into Tue, with the potential for some of these to be
strong, provided there isn`t too much weakening as the shortwave
trough approaches. The active southern-stream-dominant pattern
favors temps continuing a category or two above normal. -GIH
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
As of 210 AM Wednesday...
24 Hour TAF Period: Some concern this morning over the development
of some potential fog in the northeastern areas this morning. HRRR
visibilities show fog skirting KRWI but not actually occurring at
the airport. This may be in part due to earlier rainfall that
occurred mainly north of the KRWI area. Closer to sunrise there is
some hinting that at least scattered if not broken clouds in the
MVFR range may move into the northeast as well and potentially
affect KRWI and KRDU. These ceilings could persist through to almost
18Z before lifting later this afternoon. Otherwise expect VFR
conditions and northeasterly winds.
Long term: A low pressure system will cross the area on Friday
through Friday night with the potential for showers and
thunderstorms. High pressure with VFR conditions should return for