Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 261716

Area Forecast Discussion
National Weather Service Raleigh NC
115 PM 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 1025 AM Thursday...

A slightly unstable low level air mass this afternoon with sbcape
values of 1000-1500 j/kg will interact with a weakening disturbance
aloft to possibly trigger a few showers and t-storms late this
afternoon and this evening. This potential appears best west of
highway 1, with the greatest threat along the western periphery of
our forecast area. Have adjusted/expanded slight chance pops to
encompass most of the southern Piedmont and the western sandhills.
At this time, atmosphere does not appear that it will support any
severe storms as the shear is very weak/non-existent and instability

Thicknesses this afternoon projected to be near or slightly warmer
than those observed Wednesday. Thus, max temps this afternoon should
be comparable to yesterday, ranging from the mid 80s in the nw
Piedmont, to the upper 80s/near 90 elsewhere. -WSS

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). -BLS


.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 /18Z Thursday through Tuesday/...
As of 115 PM Thursday...

It`s highly likely that VFR conditions will persist across central
NC through Friday. The exception will be a small risk for early
morning fog, limiting the visibility to MVFR criteria for a brief
period. In addition, isolated convection late this afternoon through
this evening, and again Friday afternoon through the evening, will
produce instances of MVFR ceiling and visibility.

Aviation conditions on Saturday will vary between VFR and MVFR
criteria as increasing moisture results in lowering cloud bases and
an enhanced threat for afternoon and evening scattered convection.
Sub VFR conditions appear more likely Sunday and Memorial Day due to
an area of low pressure projected to be positioned off the GA/SC
coast. Circulation around this feature could send abundant moisture
into central NC, resulting in widespread cloud cover and scattered
to numerous showers and thunderstorms. Aviation conditions may
slowly improve by Tuesday, though periods of MVFR conditions are





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