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fxus62 krah 291336 

Area forecast discussion
National Weather Service Raleigh NC
935 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 935 am Wednesday...

Central NC will be under the influence of a very remote surface high
centered over northern Ontario with building heights aloft as
shortwave ridging shifts overhead. The NAM and especially the hrrr
have been a little overzealous in the depiction of of stratus
advecting into the area within the low-level northeasterly flow. Based on
recent satellite imagery trends, looks like the main area of stratus
will remain confined along the immediate coast, with just small
pockets of stratus inland, eventually lifting into a scattered
stratocu layer. Will go more optimistic with sky cover, with mostly
sunny skies this afternoon.

High temperatures ranging from mid to upper 60s NE , to mid/upper
70s southwest.

It should remain mostly clear tonight, but an area of expanding
stratus, developing within the 925-850mb southeasterly upslope flow along the
higher terrain, is expected to spread into the western Piedmont
between 08 to 12z. Lows ranging from the mid 40s NE to mid 50s SW.


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 European model (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 east-northeast with a negative tilt through the
central Carolinas Fri morning, accompanying enhanced upper
divergence and high precipitable water 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/east 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 County Warning Area late Fri night as the mid level low/trough starts heading
off the Delmarva coast, with a trailing front working eastward
through the northwest 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 northwest 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 southeast.

Mon through Tue: more stormy weather as yet another potent wave
tracks from the S plains east 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 /12z Wednesday through Sunday/...
as of 727 am Wednesday...

24 hour taf period: mainly VFR conditions through the taf period
however there is some concern for MVFR ceilings as northeasterly
flow comes into play this morning. In general, stratus has been
sparse and not formed as quickly as anticipated this morning. GOES-
16 imagery shows a large area of stratus offshore of northeast NC
spilling into extreme coastal areas. This may not make it into the
County Warning Area today yielding VFR conditions through much of the taf period
until the early Thursday morning hours when MVFR ceilings will be
possible at The Triad sites. Some wind gusts to 15 knots are
possible this afternoon.

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
the weekend.


Rah watches/warnings/advisories...



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