Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 231906

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

The remnants of Tropical Cyclone Cindy will track northeast through
the Tennessee valley this afternoon and eastward into the Mid-
Atlantic tonight. A cold front will approach the region from the
northwest on Saturday and progress slowly southeast through the
Carolinas Saturday night as the remnants of Tropical Cyclone Cindy
track offshore the Mid-Atlantic coast.


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


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


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.


As of 135 PM EDT Friday...

24-HR TAF Period: VFR conditions are expected to prevail this
afternoon/evening. Sub-VFR conditions associate with showers/storms
will be possible between 04-10Z, primarily at the INT/GSO/RDU
terminals. MVFR/IFR ceilings will be possible at all terminals
during the pre-dawn hours, though confidence is lower than average,
particularly at eastern terminals. Expect southwest winds at 10-15
knots with gusts to 20-23 knots this afternoon. Gusts may cease for
a few hours after sunset, however, winds are expected to increase to
15-20 knots sustained with gusts to 30 knots AOA midnight as the
height/mslp gradient tightens between Cindy`s remnants to the N/NW
and high pressure offshore the Southeast coast. Winds will decrease
to 10-15 knots by sunrise Sat. VFR conditions are expected to
prevail at the end of the 18Z TAF period.

Looking Ahead: Thunderstorms will be possible at all terminals late
Saturday afternoon/evening, ~21Z at the INT/GSO terminals, ~23Z at
the RDU terminal, and ~00Z at the FAY/RWI terminals. Isolated wind
gusts to 35-50 knots will be possible in association with the
strongest storms. Sub-VFR ceilings cannot be ruled out Saturday
night and Sunday at eastern terminals. VFR conditions will prevail
Sun-Wed as dry high pressure builds into the Carolinas from the
northwest. -Vincent





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