Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Highlight Changed Discussion --
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FXUS62 KRAH 271909
Area Forecast Discussion
National Weather Service Raleigh NC
309 PM EDT Fri May 27 2016
.SYNOPSIS...High pressure will extend across the area through
today. A low pressure system developing off the Southeast coast will
drift toward the northwest, approaching the Carolinas and Southeast
coast over the weekend.
.NEAR TERM /through Saturday night/...
As of 1040 AM Friday...
Little change required to the near term forecast.
12Z upper air analysis depicts a weak low-mid level trough across
the western Piedmont. Meso-analysis has some moisture pooling along
this feature. GSO sounding this morning depicts a mid level cap
weaker compared to the past couple of days. With current parameters
indicating a slightly better potential for isolated convection, have
expanded the slight chance PoP farther to the south and east to
encompass most of the southern and western Piedmont.
Temperatures on track to reach well into the 80s to near 90 degrees.
Tonight: Baggy mid level low pressure over the Bahamas (southwest of
the offshore anticyclone) will begin a slow drift toward the FL
coast, with a band of vorticity on its NNE side (in tandem with a
deepening surface low center) rotating about the low toward the SE
coast. This still-light-but-increasing flow aloft from the ESE will
draw in high clouds from the offshore convection, such that skies
will trend toward fair or partly cloudy tonight from SE to NW. Low
Sat/Sat night: Rain chances are expected to increase as the baggy
mid level low shifts ashore over FL/GA/SC, while the surface low
located NNE of the low progresses further to the NW, likely reaching
the Southeast coast by Sun morning. This low has the potential to
take on some tropical characteristics (see products and bulletins
from the National Hurricane Center regarding this possibility), but
regardless of its nature, the increased influx of low level Atlantic
moisture particularly into the SE and southern CWA along with
improving (yet still unfocused) upper divergence and rising PW to
1.5-2.0" should lead to increasing rain chances, focused on the
southern CWA, on Sat and especially Sat night. Will trend pops up
gradually from SE to NW starting Sat, reaching likely in the SE and
good chance NW by late Sat night, with skies trending toward mostly
cloudy. While this system could generate gusty winds and some
locally heavy rainfall near its center, given that most models keep
its center near or just off the GA or southern SC coast through Sat
night, such impacts could easily be suppressed well to our south.
That said, we`ll be closely monitoring this system as we head into
the long holiday weekend. Expect highs Sat 82-86 and lows Sat night
.SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
As of 345 AM Friday...
Increasingly wet/stormy for the latter half of the weekend.
A strong vorticity max parent to a complex mid to upper-level low
now centered near the Bahamas will, according to a preferred
GFS/ECMWF consensus, be "kicked" out of the mean low position --
across the Carolinas-- by an upstream southern stream shortwave
trough now over the Rio Grande. Meanwhile at the surface, the well-
advertised low that the Air Force reserve Hurricane Hunter aircraft
is scheduled to investigate this afternoon, is forecast to drift
northwestward, to a position near the central SC coast by 12Z Mon.
An inverted surface trough axis, likely in the form of a maritime
tropical warm front, will extend northward from the low and bisect
A deep southeasterly moisture plume, characterized by precipitable
water values around 1.75 to 2 inches, will be directed into the
Carolinas, between the mean upper low position near the Bahamas and
a sub-tropical ridge centered near Bermuda. The presence of the
moist axis will ripen the environment for numerous showers and
storms, which will be aided by forcing for ascent accompanying the
mid-upper level vorticity max, and focused by low level convergence
along the aforementioned inverted trough/warm front. Despite the
presence of the warm front, the low level flow and associated shear
are expected to remain weak, at least comparatively so for a nearby
tropical cyclone environment, so no heightened risk of severe
weather is anticipated. Clouds and convection will yield high
temperatures around 80 degrees, albeit with noticeably higher
humidity levels driven by upper 60s to around 70 degree surface
dewpoints east of the warm front. Lows 65 to 70 degrees. -26
.LONG TERM /Sunday Through Friday/...
-- Changed Discussion --As of 305 PM Friday...
Sunday through Tuesday: The likely tropical/sub-tropical low is
expected to be located very near the South Carolina coast Sunday
morning, shown by nearly all of model guidance. However, where the
sub-tropical/tropical/remnant low tracks after approaching/moving
onshore is still in question. Given the approaching system and
influx of tropical moisture into central NC, we should see numerous
to widespread showers and thunderstorms on Sunday as the inverted
surface trough pivots westward and into our area. This will lead to
the potential of heavy rain with any showers and storms as PW`s are
expected to surge to around/over 2 inches, along with at least some
threat of at least isolated severe storms. With regard to the severe
threat, there is still some uncertainty about how much instability
we will have and how strong the deep and low level shear will be,
with the eventual track and intensity of the system playing a major
role. High temps Sunday should be limited to around 80 degrees
thanks to the convection and mostly cloudy/overcast skies, but with
quite humid conditions.
The latest GFS and NAM shows the system lifting northward across the
coastal plain of the Carolinas on Monday night into Tuesday and
being absorbed in a passing northern stream s/w. The latest ECMWF is
hinting at this potential now as well, which differ some from its
previous run and has more of a drier solution across most of central
NC by Monday, with any heavy rain/rain generally from the I-95
corridor and eastward. However, will maintain continuity for now
with previous forecasts and still show at least likely pops across
the eastern half of the area. Chances for showers and storms are
expected to decrease further Monday night into Tuesday with any
lingering trough axis located along the coast (higher chances east
vs west for central NC). High temps on Monday and Tuesday are
expected to be in the lower to mid 80s, with lows in the mid to
Tuesday night through Friday: Will trend chances for showers and
storms more towards climo with poor run to run model continuity,
along with model differences. This will yield generally diurnal
chance pops with high temps in the lower to mid 80s and lows in the
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.AVIATION /18Z Friday through Wednesday/...
As of 1240 PM Friday...
High confidence that VFR conditions will persist across central NC
through Saturday. An isolated shower or thunderstorm is possible in
vicinity of KINT and KGSO between 20z-01z though confidence not high
enough to mention in the TAF for either site. Also, after 08z, could
see patches of fog, limiting the visibility to 2-5 miles in sections
of the sandhills and the coastal plain.
Aviation conditions deteriorate later Saturday as increasing low
level moisture overspreads the region from the southeast. this will
result in ceilings lowering into the MVFR category along with an
increasing threat for showers. Adverse aviation conditions appear
highly probable across central NC Saturday night through Sunday
Low confidence in the forecast Memorial Day through Wednesday as
weather conditions will be dictated by the position and movement of
an area of low pressure in vicinity of the southeast U.S. Aviation
conditions will vary between VFR and MVFR though tough to determine
which category will be most likely during this period.