Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 290743
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
335 AM EDT MON AUG 29 2016

.SYNOPSIS...
High pressure will persist over the Piedmont through tonight. An
area of low pressure over the Atlantic will drift west toward the
Carolina coast through Tuesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 330 AM Monday...

No a lot of change in the synoptic pattern in the past 24-48
hours, with an upper ridge centered over the mid-Atlantic states,
a upper low off the Southeast coast, and a dry air ridge in the
low-levels extending into the region from the northeast. TD Eight
is well to the east of ILM and is forecast to move slowly west
toward the coast over the next 48 hours, strengthening a bit as
in encounters more favorable shear/moisture and the Gulf Stream.
Easterly flow around the aforementioned upper low will continue to
supply moisture across the coastal plain, resulting in a strong
moisture gradient over the Piedmont, with deeper mixing over the
western Piedmont and dewpoints dropping into the lower 60s or even
upper 50s, while dewpoints hover in the lower 70s in the coastal
plain. Weak instability and moisture convergence will support
scattered showers and a few isolated storms east of I-95, though
most CAMs show less coverage than yesterday. Highs should be
nearly identical to yesterday or a touch cooler given the
abundance of mid clouds noted on IR imagery this morning; 87-90.

Much like this morning, isolated showers and late-evolving stratus are
expected in the coastal plain again tonight. Lows 66-72.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
As of 330 AM Monday...

The upper low east of Savannah will stall on Tuesday, while TD
Nine inches closer to the NC coast, awaiting an anticipated break
in the sub-tropical ridge before moving north on Wednesday. Even
with the storm moving closer to the coast, models show little
impact inland with the dry air ridge remaining in place for
another day. Thus, is appears just widely scattered showers/storms
moving into the coastal plain again on Tuesday, with highs in the
upper 80s to around 90. Interestingly, but still of little
consequence, is the tendency for most models to generate another
low off the Southeast, with 850mb PV denoting three distinct
centers, including TD Eight in the GOMEX and TD Nine off the
Carolina Coast. The next few days will certainly be interesting
as these two or three systems respond to the synoptic flow and
local environments. Lows Tuesday night, in the upper 60s and
lower 70s.

&&

.LONG TERM /Wednesday through Sunday/...
As of 330 AM Monday...

What is now TD8 is expected to be near or over the northern Outer
Banks as a tropical storm early Wed, part of a broader shear axis
extending from TD9 in the east central Gulf along the coastal
Carolinas. Curiously, the NAM/GFS/Canadian also show a third surface
low just off Hilton Head SC, this one perhaps spawned from current
convection east of TD9 drawn to the NNW by the cold core upper low
now spinning east of Savannah. While this sort of development
between two existing tropical systems is a longshot, regardless, the
better rain chances (25-35%) Wed/Wed night are apt to be over the SE
CWA, along the mid level shear axis beneath upper divergence, with
lower chances (10-20%) over the central/NW CWA where moisture will
be much less (PW < 1.5") with mid level flow from the NW.
Thicknesses will remain well above normal, supporting highs around
90 to the lower 90s with lows in the lower 70s. Now-TD8 is expected
to move swiftly to the NNE away from NC late Wed. Attention then
turns to the mid level polar stream trough that will dig and deepen
over the Great Lakes and Northeast late Wed through Thu night,
pulling a bonafide cold front into and through NC from the NW. While
along-front moisture pooling appears meager, a few showers and
storms may be generated as the front (and its accompanying upper
divergence max in the right entrance region of a jetlet over/off the
Northeast) encounters better moisture over the Piedmont late Thu,
and will retain good chance pops (30-45%) Thu through Thu night,
highest in the E half. Thicknesses remain elevated with a prefrontal
thermal ridge in place, and expect highs from the upper 80s to lower
90s. The digging polar trough is expected to draw what is now TD9 to
the NE across northern FL and off the SE coast Thu into Fri,
allowing the front to progress fully to the SE through our area,
with cool surface high pressure ridging building in from the Great
Lakes/Ontario. Expect low precip chances Fri, likely extending
through Sat/Sun, as the surface high pressure ridge narrows but
continues to extend through central NC, while the mid level trough
weakens and stalls near the mid-Atlantic and Southeast coast,
keeping our area on the subsident side of the trough. As thicknesses
drop to well below normal Fri and more so Sat/Sun, expect highs in
the lower-mid 80s, with lows slipping into the 65-70 range. -GIH

&&

.AVIATION /07Z MONDAY THROUGH FRIDAY/...
As of 140 AM Monday...

East-northeasterly low-level flow will continue to advect moisture
inland this morning, resulting in low ceilings/vsbys across eastern
NC.  Meanwhile, a few showers will be possible around RWI.
Confidence is high for IFR and LIFR conditions at RWI and FAY by
09Z.  Expect low ceilings to reach RDU by 11Z, but confidence in low
clouds at GSO and INT much lower given high clouds currently spread
over the Piedmont and drier low-level air in place.  Similar to
yesterday, the low clouds will slowly disperse through 15z, with a
chance of showers and storms confined mainly from RWI to FAY and
east during the afternoon. Otherwise, conditions will be mostly VFR
with a northeasterly wind that may periodically gust to 15-20kt.

Similar conditions are expected tonight, with low clouds likely at
RWI/RDU/FAY.

Outlook:  The approach for Tropical Depression 9 off the Carolina
coast makes the aviation forecast for mid-late week a little
uncertain, but at the moment it appears the impacts will be minor
and VFR conditions will prevail, with overnight stratus possible
over eastern NC.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
None.

&&


$$
SYNOPSIS...SMITH
NEAR TERM...SMITH
SHORT TERM...SMITH
LONG TERM...Hartfield
AVIATION...SMITH



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