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265
FXUS62 KRAH 270603
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
203 AM EDT Thu Jul 27 2017

.SYNOPSIS...
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Surface ridge axis over the area will shift offshore later this
morning. Meanwhile a stalled surface front draped across SC will
dissipate today with a weak surface trough developing across the NC
Piedmont this afternoon. A cold front will approach from the
northwest Thursday night and cross our region Friday night.
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&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1005 PM Wednesday...

1022 mb surface high pressure along the nrn middle Atlantic coast
will continue to extend swwd through the east-central Carolinas
tonight. Return flow around the ridge axis, in a warm advection
regime indicated by RAOB and VWP-observed veering low-mid level wind
profiles over the wrn Carolinas and VA, will favor the
development/percolation of areas of 3-5 thousand ft stratocumulus
over central NC tonight. CAM solutions suggest some of these clouds
may deepen into shallow showers overnight, capped above by a
continued 8-10 thousand subsidence inversion aloft evident in both
GSO and RNK 00Z-observed RAOB data, mainly over the wrn and nrn
Piedmont (where the WAA regime will remain maximized). Isolated
showers may consequently result there, with otherwise partly cloudy
skies and lows in the upper 60s to lower 70s.

&&

.SHORT TERM /THURSDAY AND THURSDAY NIGHT/...
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.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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 warm up towards midweek bumping highs back into
the upper 80s Wednesday. Mins will be in the mid to upper 60s.

&&

.AVIATION /06Z THURSDAY THROUGH MONDAY/...
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As of 203 AM Thursday...

Weak return flow/WAA maximized across western NC, along the western
periphery of the sfc ridge axis centered across eastern NC will
result in 3-5 thousand ft stratocumulus across central NC overnight,
with an isolated/stray shower possible near KINT and KGSO.
Otherwise, expect predominately VFR conditions this morning and much
of the day on Thursday with a broken stratocu expected owing to
strong heating.

KINT and KGSO will see the best chance of convection this afternoon,
with upstream disturbances and associated convection expected to
track SE into the western Piedmont during 20 to 24z time frame.
Have included a prob30 group for thunder for this time frame.

There after, confidence decreases with the evolution of this
convection whether it will persist and advance east into the central
Piedmont and coastal Plain or if it will weaken and dissipate
altogether. There is also the potential for additional convection to
to propagate east/se into the area Thursday night, especially across
the northern terminals.

Outlook for Friday through Monday... MVFR to IFR conditions
associated with numerous showers and thunderstorms late
Friday/Friday night as a cold front is expected to push SE through
the area. Aside from some isolated convection Saturday night/Sunday
as the upper low/trough digs south over the area, expect
predominately VFR conditions through Monday.
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&&

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

&&

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