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588
FXUS62 KRAH 240012
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
810 PM EDT Fri Jun 23 2017

.SYNOPSIS...
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Low pressure will pass to our northwest, crossing the central
Appalachians later tonight into Saturday morning, before moving off
the Mid Atlantic coast. This will drag a trailing cold front through
central NC late Saturday through Saturday night. High pressure will
follow, bringing cooler and drier air into our region for next week.
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&&

.NEAR TERM /THROUGH TONIGHT/...
As of 135 PM EDT Friday...

Today: A large moisture/instability gradient was present over
central NC at 16Z, with MLCAPE ranging from ~500 J/kg in the Triad
to 1500 J/kg along/east of I-95. H85 dewpoints ranged from 11-12C in
the W/SW Piedmont to 14-15C in the Coastal Plain. Though further
destabilization may occur in the Coastal Plain through early
afternoon, instability should decrease by mid/late afternoon as a
much drier H85 airmass (dewpoints 6-10C in GA/SC) advects into
central NC from the southwest. With a ridge centered just offshore
the SE coast, small amplitude waves and/or MCVs embedded in SW flow
aloft in advance of Cindy`s remnants should remain well NW of the
area this afternoon. As a result, forcing in central NC will be
confined to mesoscale features such as the seabreeze and diff
heating boundaries. With the above in mind, a slight chance of
convection cannot be ruled out in assoc/w the seabreeze in the far
SE Coastal Plain this afternoon where instability will be relatively
greatest. Expect highs ranging from the mid/upper 80s NW to lower
90s SE. Southwest winds will increase to ~15 mph sustained with
gusts to 25 mph by late afternoon.

Tonight: Scattered convection will be possible overnight as Cindy`s
remnants track northeast from the TN valley into the Virginias and
low-level moisture/upper forcing increase across W/NW portions of
the state. Expect the relative best potential for convection
along/west of Hwy 1 between midnight and sunrise. Low-level flow
will strengthen considerably overnight as the height gradient
tightens between Cindy`s remnants to the N/NW and high pressure
offshore the SE coast. Forecast soundings suggest a southwest wind
sustained at 15-20 mph with gusts up to 30-35 mph, primarily after
midnight. Wind gusts exceeding 35 mph cannot be ruled out in assoc/w
convection in the NW Piedmont, however, damaging winds appear
unlikely given poor diurnal timing /weak low-level lapse rates/, as
reflected in the Day 1 outlook which confines severe wind probs
along/west of the Blue Ridge. -Vincent

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...
As of 135 PM EDT Friday...

A cold front will approach the central Appalachians from the NW late
tonight. With the remnants of Tropical Cyclone Cindy progged to
track a bit further N/NW of central NC than previously anticipated,
the cold front is not expected to progress into central NC until Sat
evening/night. With central NC on the eastern periphery of the pre-
frontal trough, rich low-level moisture is likely to persist through
the afternoon. Strong insolation and rich low-level moisture are
expected to yield moderate instability by mid/late afternoon,
ranging from ~1000 J/kg in the NW Piedmont to ~2000 J/kg in the SE
Coastal Plain, in the presence of 30-40 knots of deep-layer shear.
Convection allowing models suggest scattered convection will develop
within the pre-frontal trough in vicinity of the I-77 corridor by
mid/late afternoon (19-20Z), then quickly grow upscale into a SW-NE
oriented line that progresses E/SE through central NC between 21-00Z
(roughly). Though diurnal timing will be optimal, rich boundary
layer moisture /relatively low T/Td spreads/ will yield marginal
DCAPE (500-750 J/kg) and line-parallel (southwesterly) deep-layer
shear will not favor new updraft development at the leading edge of
the consolidated cold pool. As a result, the potential for damaging
winds appears relatively marginal /isolated/. Expect highs ranging
from the mid/upper 80s (NW) to lower 90s (SE). -Vincent

Saturday night and Sunday, a sfc boundary trailing behind a low
pressure system crossing the northern Mid-Atlantic, will cross
central NC Saturday night and Sunday. This front interacting with a
moisture rich air mass will support the development of scattered-
numerous showers and thunderstorms Saturday evening. Bulk of
convective will dissipate overnight Saturday night though isolated-
scattered showers still probable due to the presence of the front
and available moisture. By Sunday, the main focus for convective
development should be primarily east and south of Raleigh as the
front should lie in this vicinity. Nwly flow behind the front will
advect a drier more stable air mass into the Piedmont Sunday,
leading to drier conditions. -WSS

&&

.LONG TERM /SUNDAY night THROUGH FRIDAY/...
As of 305 PM EDT Friday...

The drier air mass will overspread the remainder of central NC late
Sunday and Sunday night. Monday shaping up to be warm and dry with
wly flow aloft and a sfc high positioned over the TN Valley. A s/w
in the northern stream projected to drop sewd across the lower OH
Valley Monday night, and cross central NC Tuesday. 12Z ECMWF more
adamant about the potential for lift and isolated/scattered showers
compared to the drier GFS. Based on the favorable timing, potential
will exists for isolated-scattered showers, primarily late morning
through the afternoon.

A modifying Canadian high pressure system will initiate a stretch of
dry and relatively pleasant conditions (ie. less humid) across
central NC Wednesday into Thursday. By Friday, return flow on the
back side of the retreating high will signal a return to warm and
humid conditions by the end of the week.

No signals noted for extreme heat across our part of the country
through the next 5-7 days. In fact, high temperatures Tuesday and
Wednesday will likely average 3 to 8 degrees below normal. The
modifying air mass Thursday and Friday will permit temperatures to
return to seasonal norms.

&&

.AVIATION /00Z Saturday through Wednesday/...
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As of 810 PM Friday...

The most significant aviation hazard over the next 24 hours will be
gusty winds from the SW, occurring over the next 12-15 hours,
including a strong crosswind at INT.

VFR conditions are expected to dominate central NC terminals through
00z Sun. Low pressure, the remnants of what was once Tropical Storm
Cindy, will pass by to our NW and N tonight through Sat morning.
While INT/GSO will likely see a period of MVFR cigs/vsbys in showers
(with a lesser risk of thunder) between 04z and 09z tonight, this
precipitation is expected to dissipate as it approaches RDU, leading
to a much lower chance of MVFR conditions there, and the chance for
sub-VFR conditions at RWI/FAY is even lower. Surface winds will
increase from the SW through the evening, with sustained speeds
reaching 15-22 kts and gusts as high as 25-35 kts, especially after
midnight, lasting until just before or around daybreak Sat. Aviation
interests should use extreme caution at INT, as this will present a
significant crosswind at that site, and these winds may induce some
low level turbulence at other locations. As the low shifts off the
Mid Atlantic coast early Sat, it will drag a cold front slowly into
the area, causing a shift of winds to be from the W or WSW with time
Sat, but with lower sustained speeds and only sporadic gusts at
most. VFR conditions will dominate Sat, although scattered
thunderstorms producing brief sub-VFR conditions and enhanced gusts
are expected near FAY Sat afternoon, with a lesser chance of storms
near RDU/RWI. INT/GSO will remain dry.

Looking beyond 00z Sun (Sat evening), mid and high clouds will
continue to streak across the area, especially southern and eastern
NC, through Sun. Confidence is high that VFR conditions will hold
through at least Wed, with high pressure in control both at the
surface and aloft. -GIH
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&&

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

&&

$$

SYNOPSIS...MLM/GIH
NEAR TERM...Vincent
SHORT TERM...Vincent/WSS
LONG TERM...WSS
AVIATION...Hartfield