Area Forecast Discussion
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FXUS62 KRAH 281129
Area Forecast Discussion
National Weather Service Raleigh NC
729 AM EDT Tue Mar 28 2017
An upper-level disturbance crossing the region will bring unsettled
weather today, followed by quiet conditions tonight and Wednesday as
a cool front settles southward into the area. Another storm system
moving through the central U.S. Wednesday will approach our area
Thursday, bringing another round of stormy weather late Thursday
through Friday night.
.NEAR TERM /THROUGH TONIGHT/...
As of 400 AM Tuesday...
A low pressure system that is very evident on satellite, water
vapor, and radar imagery is working its way through the Ohio Valley
at this time and helping to push a band of showers and thunderstorms
into the western Piedmont at this time. All storms are sub-severe at
this time but the line is expected to hold together through the
early morning hours as it pushes eastward. This initial line of
showers and storms is expected to make it through the CWA by early
afternoon and exit to the east. Behind this line, another line is
expected to form during the peak heating of the afternoon and
strengthen as it moves eastward. Looking at forecast soundings, the
most favorable conditions will be along the I-95 corridor where 700-
1000 J/kg of instability, upwards of 40 kts of bulk shear and good
low and mid-level lapse rates will set the stage for the possibility
of some severe weather. SPC has placed all of central NC in a
marginal risk for severe weather. LCLs are very high and hodographs
do not indicate much helicity at least in the 0-3 km range,
therefore do not expect tornadoes with this system. The most likely
severe threat will be damaging winds with some small hail possible
as well. This fits in well with the history of this storm system.
After this secondary line exits to the east, conditions will
gradually begin to clear with VFR conditions returning to the area.
Temperatures will be tricky depending upon convective coverage but
despite that, another warm day is expected with highs in the mid 70s
across the north to lower 80s in the southern counties. Lows in the
.SHORT TERM /WEDNESDAY AND WEDNESDAY NIGHT/...
As of 400 AM Tuesday...
Quiet weather day on Wednesday as surface high pressure builds in
from the north behind the exiting frontal system and an upper level
ridge extends northward out of the southern Caribbean. A bit cooler
with the airmass change with highs in the low 70s across the
northeast to upper 70s in the southwest. Lows are expected to be in
the mid 40s across the northeast to middle 50s in the southwest.
.LONG TERM /Thursday through Monday/...
As of 345 AM Tuesday...
Thu through Sat: The backdoor cold front is expected to settle just
south of NC early Thu as cool high pressure noses in from the north.
In the mid levels, a shortwave ridge shifts across the SE and
Carolinas Thu, while a potent low pushes slowly eastward through the
central and southern Plains. Major model differences start to emerge
between the GFS and ECMWF Thu, resulting in a low confidence
forecast. Both models take the mid level low and trough eastward
through the Mid/Lower Miss Valley / Mid South / Gulf States and
Carolinas / Southeast through early Sat, however the GFS digs energy
into this low much more deeply than what is shown by the ECMWF, and
this in part results in notable differences with the push of the
front back north through NC, with the more southern-track GFS
keeping the front to our south through Thu night (with a cool stable
wedge regime in the NC Piedmont) followed by a slow northward push
Fri, while the slightly weaker/more northerly ECMWF takes the milder
air northward into central NC as early as late Thu. While the high
to our northeast is not particularly strong nor is it being
significantly reinforced aloft, this air mass should still be dense
enough for the cool pool to stay lodged into the NC Piedmont through
Thu. Will have highs Thu from the mid-upper 50s NW ranging to near
70 SE, with a slight chance of rain or drizzle in the west with
overrunning flow strengthening over W NC as the 850 mb anticyclone
shifts off the Carolina coast. As the mid level low/trough crosses
the region with a negative tilt, it will be accompanied by a complex
occluding surface frontal system, with a more southern track and
less potential instability on the GFS (which develops strong forcing
for ascent near the E Gulf Coast/FL Panhandle Thu/Thu night) and a
more northern track with greater potential instability on the ECMWF.
Have generally followed the slightly weaker ECMWF, although both
models have been trending stronger with the shortwave trough in
recent runs, so confidence remains low. There does appear to be
enough moisture (PW of 1.25-1.5") and forcing for ascent, including
DPVA, enhanced upper divergence, and low level mass convergence, for
a continuation of likely pops, focused on Thu night through Fri
evening, tapering down WSW to ENE Fri night into early Sat as the
mid level shortwave trough and surface frontal system push to our
east with a weak cool front settling southward through the area.
Highs from the mid 60s to lower 70s Fri with cloudy skies and
numerous showers/storms, and in the low-mid 70s Sat with partial
sunshine and rising heights aloft as another mid level ridge axis
approaches in the wake of the exiting trough.
Sat night-Mon: Expect generally quiet weather Sat night/Sun as weak
surface high pressure builds in from the north in tandem with the
mid level shortwave ridging. Yet another shortwave trough crosses
the S Plains into the lower Miss Valley Sun night into Mon, while
the weak frontal zone to our south tracks back northward. Expect
fairly seasonable temps Sun, perhaps still a little above normal as
the incoming surface high will be cut off from a polar air source.
Warmer thicknesses Mon, behind the weak warm front, will be offset
with increasing clouds with the trough`s approach, so expect highs
from the lower to upper 70s Mon. -GIH
.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
-- Changed Discussion --As of 730 AM Tuesday...
24 Hour TAF Period: A line of showers extending through the central
part of the CWA will continue to slowly move eastward this morning.
Not much potential left for thunder with this round of rain. Later
in the day, expect a line of showers to develop in the Triad around
18z and push eastward reaching the Triangle by 20Z and pushing
eastward after that. KRWI and KFAY will be the most likely locations
to experience any thunder this afternoon. Some storms could become
severe with damaging winds the most likely threat but coverage of
severe, and thunderstorms in general should be fairly limited. After
00z showers and storms will exit to the east and winds will become
more northwesterly. Some wind gusts this afternoon of 15-20 knots.
Some MVFR ceilings could be possible with heavier showers but
otherwise expect mainly VFR conditions today.
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
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