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-- Discussion containing changed information from previous version are highlighted. --
000
FXUS62 KRAH 261901
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
300 PM EDT Wed Jul 26 2017

.SYNOPSIS...
A stalled surface front draped across SC will return north as a warm
front later tonight, then dissipate over central NC on Thursday. A
cold front will approach from the northwest Thursday night and cross
our region Friday night.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 255 PM Wednesday...

A return to a typical summertime weather pattern to occur this
period with an increasing chance for scattered convection in the
short term.

A strong upper level ridge extends west-to-east across the southern
tier of the U.S., with the eastern extension across the Carolinas
this afternoon. This upper ridge extension will weaken/retreat west
as a series of disturbances in the jet stream across the northern
tier of the U.S. begin to carve out an upper level trough along the
eastern seaboard. The attendant sfc high will continue to drift
offshore tonight through early Thu. The return sly flow will advect
a more humid air mass residing across GA/SC, characterized by
dewpoints in the lower 70s, into central NC by Thu. The stalled
boundary delineating the northern extent of the humid air mass will
advance northward overnight into central NC, then become ill-
defined. This feature may trigger an isolated shower or storm this
evening over the southern Piedmont. Overnight temperatures will be
within a degree or two of 70 degrees.


&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
-- Changed Discussion --
As of 255 PM Wednesday...

The atmosphere over central NC will become increasingly moist and
unstable as the upper level ridge departs and height falls occur
ahead of the approaching upper disturbances and sfc cold front.
While an isolated storm or two possible in vicinity of the VA order
Thu afternoon, better forcing/support aloft doesn`t arrive until Thu
evening/Thu night. The atmosphere by late Thu projected to be
slightly unstable with MLCAPE values approaching 1000 j/kg across
the northern counties. Meanwhile, bulk shear not too shabby for this
time of year, in the neighborhood of 25-30 kts. This could be
supportive of broken line segments and potential strong wind gusts.
This threat for strong storms should be isolated, however, and
primarily confined to locations along and west of I-85 Thu evening.

The threat for isolated/scattered convection will persist well into
the overnight Thu night across our northern counties, particularly
near the VA border as the initial disturbance crosses VA. Will
maintain chance PoPs for now roughly north of highway 64 but may
need to bump up PoPs in proximity of the VA border to likely after
06Z Fri, especially if the GFS verifies.

The warming/modifying air mass will result in afternoon temps Thu
near 90-lower 90s. Variably cloudy skies and continued light sly sfc
wind will maintain warm/muggy conditions Thu night. Min temps
generally in the lower 70s.
-- End Changed Discussion --

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
-- Changed Discussion --
As of 300 PM Wednesday...

A vigorous mid-level shortwave will dig SE across the Ohio Valley
and slow as it starts to cut off and reaches the mid Atlantic early
this weekend. It will continue digging at this slowed pace SE across
the area, exiting the coast on Sunday.

A surface low will develop over northern Virginia along the cold
front associated with this system on Friday, with NC remaining in
strong warm and moist advection ahead of the front through the day.
Convection will become likely by Friday afternoon with low level
flow increasing convergence along the Piedmont trof ahead of the
front, with likely PoPs lingering through frontal passage...which
will be around midnight in the northwest, and near daybreak Saturday
in the coastal plain. Stronger shear will remain north of the area
in the vicinity of the triple point low and stronger upper
diffluence associated with the upper short wave as they skirt
northern Virginia. Strong instability with deep moisture could
potentially produce a few severe storms capable of damaging
downdrafts. Still a lot of uncertainty as to where it will
concentrate, but convection will be widespread, so stay tuned. Highs
Friday will be hindered by cloud and precip coverage, with the
northern tier stalling out in the mid 80s, while some morning sun
should produce some low 90s across the south.

Could see patchy showers and maybe an isolated storm on Saturday as
the upper trof swings through, otherwise clearing with a drier and
cooler airmass settling into place which will linger at least
through early next week. Lower humidity will add to the comfort
level as highs Saturday through Tuesday top out mostly in the mid
80s, with a possible warmup towards midweek bumping highs back into
the upper 80s Wednesday. Mins will be in the mid to upper 60s.
-- End Changed Discussion --

&&

.AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
As of 1230 PM Wednesday...

An area of high pressure extending across central NC this afternoon
will provide VFR conditions through Thursday. The exception will be
pockets of MVFR/IFR visibility due to fog overnight tonight through
daybreak Thursday or patches of MVFR ceilings. The fog appears most
probable in vicinity of of KFAY and KRWI between 09Z-12Z Thu.

While VFR parameters anticipated for much of Thursday, an
approaching cold front will increase the risk of scattered
convection across the northern counties late Thursday but more so
Thursday night. At this time, it appears scattered convection may be
in the vicinity of the Triad terminals and KRDU after 02Z Friday,
persisting into Friday morning.

Additional scattered convection and associated MVFR parameters
appear probable across central NC Friday through Friday night as the
sfc cold front drifts southward. A drier, more stable atmosphere and
attendant VFR parameters expected Saturday through Monday.

&&

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

&&

$$
SYNOPSIS...WSS
NEAR TERM...WSS
SHORT TERM...WSS
LONG TERM...mlm
AVIATION...WSS