Area Forecast Discussion
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FXUS62 KRAH 280747
Area Forecast Discussion
National Weather Service Raleigh NC
345 AM EDT Tue Mar 28 2017
An upper level trough will cross the region Tuesday, along with a
trailing cold front. High pressure will build in from the north on
Wednesday, then shift offshore Thursday. A strong storm system is
expected to affect the region late in the week.
.NEAR TERM /THROUGH TONIGHT/...
As of 945 PM Monday...
Diurnally driven isolated convection across the southern piedmont
earlier this evening has since died down with loss of heating.
However, we will see an increase in pops late tonight(at least over
the western piedmont) with the approach of the mid/upper level
trough into the southern Appalachians aoa daybreak. Hi-Res models
continue to show significant weakening of the upstream convection
currently across TN as it crosses the mountains, encountering weak
buoyancy in place across the area owing to nocturnal cooling. Will
show high chance pops in the west, decreasing to small/slight chance
pops in the east, given the potential for the convection to
dissipate altogether as it reaches the eastern zones.
It will be a very mild night with lows generally in the 60s.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 235 PM Monday...
The latest Hi-Res convection allowing models suggest that only a few
showers will remain from tonight`s convection that tries to cross
the Piedmont. Regardless, the timing of the approaching mid/upper
trough appears to be during the morning and early afternoon for the
western Piedmont, which is essentially not diurnally favorable for
strong or severe storms in the western zones.
Models do favor redevelop of at least scattered showers and
thunderstorms along the surface wind shift line that is forecast to
move SE into central NC Tuesday afternoon. The favored lift area out
ahead of the mid/upper trough is forecast to reach the eastern
Piedmont into the Coastal Plain and Coastal Areas during the peak
heating period. Convection may blossom as early as late morning or
around noon near the wind shift line, and should spread and develop
ESE during the afternoon.
It appears that the most favored area for optional heating and
destabilization should occur just to the east and south of the
Triangle area, just before the convection develops in the early
afternoon and tracks into the region. The earlier timing of the
front and trough should limit the strong to severe threat in the NW
Piedmont Triad region, with the focus in the eastern zones. Even in
the east where the instability and shear is expected to be higher,
most parameters for severe storms are forecast to be marginal. Highs
in the upper 70s to lower 80s in the east, with dew points nearing
60, should lead to MLCapes near 1000 J/KG. Mid level lapse rates may
still be in question but some subtle warming aloft may be a negative
factor for organized severe storms.
Still, look for at least scattered thunderstorms with the potential
for wind gusts to 40-50 mph and possibly up to 1 inch hail in a few
of the strongest storms. We will highlight areas east of the Triad
area for this potential due to timing in the Hazardous Weather
The convection should be east of the region by around sunset or so,
but the lagging wind shift line may aid in some weaker trailing
storms into the evening in the east. Otherwise, partly cloudy with
lows in the 50s expected.
.LONG TERM /Thursday through Monday/...
-- Changed Discussion --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 strngthening 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
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.AVIATION /06Z TUESDAY THROUGH SATURDAY/...
As of 135 AM Tuesday...
24 Hour TAF Period: A cluster of showers and storms is approaching
the Triad at this time and although it appears to be weakening a
bit, there is still lightning being observed in these storms. expect
storms to pass over KINT and KGSO between 6-7Z and then continue off
to the northeast and dissipate. Behind the first cluster of storms
are two more lines of showers and storms that are expected to weaken
as they move east, however given the behavior of last nights rain
and the fact that there continues to be warm moist air to the east
of the mountains, expect these showers and storms to hang on long
enough to affect at least the Triad sites if not KRDU and
potentially KFAY as well. Occurring later this would be between 8-
12Z. With these showers is the potential for some MVFR ceilings and
visibilities. Expect rain to begin moving out of the Triad after 16z
and gradually clearing out later in the day. Further east another
round of showers and thunderstorms is expected Tuesday afternoon
during peak heating with the potential for some storms to become
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