Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 271048

Area Forecast Discussion
National Weather Service Raleigh NC
650 AM 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 325 AM Friday...

Today: Precip chances still appear small and limited to the far NW
CWA. Offshore-centered high pressure will continue to ridge westward
across the Carolinas through tonight, yielding a light southwesterly
flow with no good opportunity for moisture advection into the area.
Mid level heights will stay above normal over the area, despite the
weak shear axis across the western Carolinas, which should trigger
scattered convection over the higher terrain. This activity may
drift into the Triad region late in the day, however the weak
steering flow from the south will keep much of it west of the
forecast area. Elsewhere, the warm and subsiding mid levels will
result in minimal to no CAPE, despite the warm surface temps, and
deep layer shear will be weak and insufficient to support any
organized convection. Will hold onto an isolated late day pop over
the far NW with dry weather elsewhere. Slightly above normal
thicknesses combined with partly to mostly sunny skies favor highs
of 84-88.

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
64-69. -GIH


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
central NC.

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 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 now
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


As of 410 AM Friday...

Forecast confidence decreases by Memorial Day, at least with respect
to the eventual position of the probable tropical or sub-tropical
low near/over the Carolinas. Solutions from the past couple of runs
of the ECMWF indicate the low will be near the south-central NC
coast by 12Z Tue, while the same runs of the GFS support a more-
southward solution, along the southern SC coast.
In either case, the inverted surface trough/warm front will likely
remain over central NC Mon and Mon night; and this feature will
continue to serve as a focus for slow-moving showers and storms over
at least the eastern two-thirds of the CWFA, which may begin to pose
a flooding threat, partiuclarly after the previous 24-hr convection.

Tue-Thu: Model differences grow through the middle of the week.
GFS solutions depict a nearly stationary low over SC, and inverted
surface trough extending northward over central NC, with a continued
high probability of showers and storms through the end of the
forecast period. On the other hand, ECMWF solutions suggest the low
will be offshore the NC coast, with relatively dry conditions to the
west/over central NC. Given the uncertainty and no clear preferred
signal in model guidance, will simply trend the forecast toward
climo, with slightly above avg PoP given the proximity of the
remnant low.

On a larger scale, a pattern change toward western CONUS ridging and
a downstream trough west of the Appalachians, with an associated
slow-moving /quasi-stationary/ surface frontal zone nearby, suggest
conditions may be unsettled late next week and next weekend -
continuing the recent run of above avg rainfall.


.AVIATION /12Z Friday through Tuesday/...
As of 650 AM Friday...

High confidence in VFR conditions dominating central NC terminals
today through tonight. A ridge of surface high pressure centered
offshore east of VA/NC will continue to extend to the west and
southwest, resulting in a light surface flow mainly from the SW over
central NC, and sufficiently dry low levels to preclude fog
development. Meanwhile, dry and sinking air in the mid levels will
suppress most cloud development, with any clouds likely to be based
at 4-6 kft AGL. An isolated storm is possible near INT/GSO late this
afternoon or early evening, but coverage will be too low to include
in these TAFs.

Looking beyond 12Z Sat morning: VFR conditions are likely to hold
through at least early afternoon Sat. Clouds will then thicken and
lower from SE to NW -- affecting FAY and RWI first -- starting late
Sat, as an offshore low pressure area tracks NW toward the Southeast
states. Areas of MVFR/IFR conditions in rain and isolated storms are
expected to spread into the FAY vicinity Sat evening before
expanding across all central NC terminals late Sat night, continuing
into Sun. Areas of sub-vfr fog are possible Sun night and Mon night,
with mostly VFR conditions during the day Mon and Tue, however the
forecast confidence drops dramatically beyond Sun regarding the path
of the offshore low... so aviation interests should monitor the
latest forecasts closely over the long holiday weekend. -GIH





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