Area Forecast Discussion
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FXUS62 KRAH 241922
Area Forecast Discussion
National Weather Service Raleigh NC
320 PM EDT Mon Apr 24 2017
A strong and deep low pressure system will slowly cross the region
through Tuesday, producing wet and unsettled weather. Behind this
low, a ridge of high pressure will extend into the region for mid to
.NEAR TERM /through tonight/...
As of 320 PM Monday...
With a few exceptions, rainfall so far has been steady and moderate,
with numerous but minor flooding confined mostly to streets and high
water in creeks. This should change over the next 9-12 hours as we
increasingly tap into a greater depth of Atlantic-source moisture
penetrating further inland, north of a surface low that will move
northward over southeastern NC tonight (although models disagree on
the exact track of this low). Low level easterly flow is expected to
strengthen this evening into tonight north of the approaching
surface low, with the strongest flow of 30-40 kts over northern
sections of central NC, mainly along and north of the Highway 64
corridor. This will continue to draw anomalously high PW values into
the area through tonight, as well as allowing the modified wedge
boundary to shift further inland. The resulting enhancement of deep
isentropic upglide will be vertically juxtaposed with focused upper
divergence to the ENE of the mid level low, fostering efficient rain
production with a warm layer nearing 3.5 km. And the additional lift
generate via elevated convective elements, most likely over our SE
and far S sections through this evening, may result in locally
heavier rain rates and higher totals. Will leave the flood watch in
place, as an additional 1.5-3.0" of rain is possible through
tonight, with higher amounts focused along bands with embedded
convection and particularly near the pivot point of any such bands
as they become more W-E oriented with time tonight as the mid level
low shifts eastward into SC. Temps should waver only a category or
so through tonight at most, with many spots seeing steady temps
through the night or a minor rise as warmer air shifts inland. -GIH
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
As of 330 AM Monday...
The vertically stacked/mature low pressure system will track slowly
north across eastern NC Tuesday and Tuesday night and then off the
Delmarva coast on Wednesday.
With the mid-level dry slot encompassing the area Tuesday morning,
there could be a lull/minimum in precip/pops across central NC to
start the day. However, diurnal heating and resultant weak
destabilization(at least across the eastern and possibly central
zones) as the wrap-around moisture band pivots NE through the area,
is expected to lead to convective re-development Tuesday afternoon
and evening. The threat for severe storms will be muted by the lack
of greater instability but given the presence of an occluded front
draped somewhere across eastern/east-central NC, cannot rule out an
isolated severe threat. Additionally, with the potential for slow-
moving/training convection with the wrap-around band, isolated
flooding, especially in low-lying or poor drainage areas will be
Highs Tuesday afternoon will be challenging, complicated by multiple
boundaries draped across the area. Expect one sharp temperature
gradient invof of where the aforementioned occluded front sets up
across eastern NC, with another tight temp gradient along the
lingering CAD airmass across the western Piedmont. Highs ranging
from upper 50s NW to mid/upper 70s east.
Rain chances will slowly taper off from SW to NE Tuesday night,
finally coming to an end across the NE zones early Wednesday morning
as the mature cyclone lifts away from the area. Lows Tuesday night
in the mid to upper 50s Tuesday night.
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
As of 330 AM EDT Monday...
In the wake of the low lifting up the Mid-Atlantic coast, low-level
swly flow and short wave ridging aloft will mark the return of
sunshine and warming temperatures. Highs in the upper 70s to lower
80s Wednesday, warming into the lower and mid 80s by Thursday.
On the southern periphery of dampening short wave energy lifting
through the MS and Ohio Valleys NE into the Great Lakes, we could
see isolated/slight chance of showers and storms Thursday night and
Friday. Otherwise, it will remain mostly dry with the main weather
headlines being the hot temperatures associated with the dominate
subtropical ridge building across the SE US.
Highs Saturday and Sunday in the upper 80s to lower 90s.
.AVIATION /18Z Monday through Saturday/...
As of 155 PM Monday...
High confidence in poor aviation conditions through at least 06z
tonight. Thick IFR and occasionally LIFR based clouds will persist
over central NC as a deep and strong low pressure system slowly
crosses the area through Tue, exiting to our northeast Tue night.
Periods of rain through 06z will affect all sites with occasional
MVFR to IFR vsbys, along with the mainly IFR cigs. Cigs will slowly
lift Tue morning to MVFR with decreasing vertical extent as drier
air just off the ground arrives from the S. The rain will decrease
in coverage and intensity later tonight, although scattered showers
will persist after sunrise Tue as the core of the upper low passes
overhead. Surface winds will be mainly from the NE at 7-12 kts
through tonight, occasionally gusting to 15-20 kts during the
evening and overnight hours, especially at GSO/RDU/RWI as an
easterly low level jet at 1000-2000 ft AGL extends into the area.
This low level jet may lead to a risk of low level wind shear at
INT/GSO/RDU/RWI from late evening into the overnight hours. Surface
winds will then decrease late tonight (after 09z) and become more
from the N or NW Tue.
Looking beyond 18z Tue, cigs should remain MVFR through Tue night,
with infrequent MVFR vsbys in scattered showers, although cigs may
drop back to IFR through Tue night especially at INT/GSO as a cool
stable air mass persists there. After the low shift to our NE Tue
night, high pressure ridging will take over, and we`ll see cigs rise
to MVFR then VFR through Wed morning. VFR conditions will then
dominate through Sat. -GIH
As of 330 AM Monday...
...Flood Watch remains in effect through 12Z Tuesday...
Widespread heavy rain is expected to develop over central NC today
into tonight. Storm total rainfall amounts of 3-5" are expected,
with locally heavier amounts possible where the primary band of
elevated convection pivots /persists the longest/. Flooding of local
creeks and streams can be expected. Main stem rivers will experience
significant rises in water levels this afternoon into tonight,
particularly the Yadkin, Haw, Neuse, Tar, Roanoke, and Cape Fear.
Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043-