Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 261049
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
645 AM EDT Thu May 26 2016

.SYNOPSIS...Bermuda high pressure will extend over the area through
Friday. Meanwhile, a storm system will develop over the sub-tropical
Atlantic and drift toward the Southeast U.S. coast through the
holiday weekend.

&&

.NEAR TERM /through tonight/...
As of 340 AM Thursday...

A string upper level ridge, weakened slightly on the northwest
periphery by disturbances moving through the TN Valley, continues to
hold across the Southeast US, while Bermuda high pressure has become
anchored offshore.  Outside of debris cloudiness this morning and a
patch of mid-clouds approaching the northwest Piedmont, skies will
be partly cloudy to mostly sunny today.  Weak and mostly uninhibited
CAPE may support a few showers and storms drifting east off the
higher terrain and into the western Piedmont late this afternoon, a
scenario generally supported by most CAM`s.  The airmass is largely
unchanged since yesterday, so highs should again be in the 84-89
range.

The surface ridge axis, accompanied by lower theta e air, will
begin to slowly shift back west over eastern NC tonight, allowing
for good radiational cooling conditions and a range of lows from 61-65
(coolest in the east).

&&

.SHORT TERM /Friday through Friday Night/...
As of 340 AM Thursday...

Strengthening of the upper ridge and shifting of the surface ridge
overhead will lessen the prospects of convection on Friday, compared
even to the little chance there is today.  If there is a chance it
will again be int he northwest Piedmont, but even then the steering
flow should keep any convection confined to the higher terrain.
H10-H85 thicknesses will be around 1415m, yielding highs of 85-
90. Lows mostly in the lower 60s.

&&

.LONG TERM /Saturday THROUGH Wednesday/...
As of 400 AM Thursday...

Downstream of a longwave trough that will migrate from the West
Coast to the Rockies, an energetic southern stream will provide a
steady feed of vorticity that will maintain a mean mid to upper-
level low in the vicinity of the Bahamas/off the southeast U.S.
coast. This upper low will evolve at the base of/beneath a strong
ridge forecast to extend from the western Atlantic Ocean to central
Canada. The flow between these features will direct a deep feed of
moist SE flow, characterized by precipitable water values between 1-
2 standard deviations above normal, into the Carolinas/Middle
Atlantic region throughout the period.

Given the presence of the deep moist axis --including humid
conditions at the surface characterized by dewpoints in the middle
60s to lower 70s, particularly from Sunday onward-- the air mass
will be ripe for diurnally-enhanced showers and storms.

In fact, the ultimate track of the now well-advertised surface low
pressure, which may acquire sub-tropical or tropical characteristics
off the southeast U.S. coast, will likely be secondary to the
effects of the moist plume.

Regardless, we should remain under the influence of ridging at the
surface and aloft for much of Saturday, though with an initial band
of showers and storms likely to spread inland /into the I-95
corridor/ during the afternoon.

The forecast for the remainder of the period will include above
average chances of showers and storms, particularly with heating of
the humid boundary layer each day, and temperatures tempered by both
onshore flow, and clouds and convection.

&&

.AVIATION /12Z Thursday through Memorial Day/...
As of 640 AM Thursday...

Strong high pressure over the Southeast US will continue to promote
VFR conditions through the TAF period.  Dewpoints have come up a few
degrees since last night, so there may be a few pockets of MVFR
visibilities by 12z despite the thin high level debris clouds
drifting overhead.  Otherwise, a light southwesterly wind will
prevail today, with just a small chance of a brief shower or storms
at KINT/KGSO after 20z as convection drifts east off the mountains.
VFR conditions will be predominate again tonight, with the low
probability of MVFR visibility late tonight, similar to what is
observed this morning.

Long term: More chances for sub-VFR conditions for the end of the
week as a plume of moisture moves in from the southwest Atlantic
that could affect the area for several days.

&&

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

&&

$$

SYNOPSIS...CBL/BLS
NEAR TERM...BLS
SHORT TERM...BLS
LONG TERM...26
AVIATION...BLS/Ellis


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