Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC
FXUS62 KRAH 281828
Area Forecast Discussion
National Weather Service Raleigh NC
225 PM EDT Tue Mar 28 2017
An upper-level disturbance and cold front will push across the
region today, and offshore this evening. Weak high pressure will
follow the front for tonight and Wednesday. Another storm system
approach our area Thursday night and Friday, bringing another round
of stormy weather.
.NEAR TERM /THROUGH TONIGHT/...
As of 225 PM Tuesday...
Little has changed in the forecast philosophy for this afternoon and
evening. There continues to be a marginal risk for isolated severe
thunderstorms this afternoon. Clearing has allowed for an increase
in instability from the Foothills into much of the Piedmont. MLCapes
have increased in some areas to near 1000 J/KG over southern VA and
portions of the NC Piedmont. Temperatures were rising through the
70s with near 80 at Fayetteville. Dew points were in the lower 50s
NW ranging to 60 SE. The wind shift line was located from near
Hickory NE to Lynchburg at 200 PM. The main area of instability out
ahead of the wind shift line will continue to progress with the wind
shift SE into our Piedmont in the next few hours. Cumulus were
developing with some organization noted along the wind shift line to
our NW. In addition, there was another area to watch from near CLT
NE to RDU where another low level boundary was draped. A couple of
showers and thunderstorms were already ongoing along these
Hi-Res models and current data suggest widely scattered
thunderstorms will continue to develop along both these features
this afternoon as they progress rapidly eastward, exiting the
Coastal Plain region by early evening.
The favorable instability and timing of the wind shift line is
expected to be mainly east of the Triad region; therefore, the
isolated severe potential should be confined to the far eastern
Piedmont to the coast 20z-23z or so. Even over these areas, MLCapes
and many other severe weather parameters especially wind shear are
only marginal. Pea to nickel hail may end up being common in most of
the stronger cells, with isolated 1 inch hail possible.
The action will shift offshore by sunset and dry/quiet conditions
will return for tonight. Lows in the 50s.
.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 /18Z TUESDAY THROUGH SATURDAY/...
As of 145 PM Tuesday...
24 Hour TAF Period: Generally VFR conditions forecast for the
KGSO/KINT areas, with VFR elsewhere outside of widely scattered
strong thunderstorms between 19z and 23z, mainly from KRDU eastward
to the coast. VFR conditions expected tonight and Wednesday with
weak high pressure.
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