Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC-- Remove Highlighting --
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FXUS62 KRAH 240729
Area Forecast Discussion
National Weather Service Raleigh NC
330 AM EDT Mon Apr 24 2017
An upper level low and attendant low pressure system will track
southeast from the Deep South to the Southeast coast this afternoon,
then lift slowly northeast along the Carolina and Mid-Atlantic coast
tonight and Tuesday.
.NEAR TERM /through Monday/...
As of 910 PM Sunday...
Flood watch remains in effect through early Tuesday morning.
Highest threat for prolonged steady light-moderate rain will occur
across the western third of central NC through the overnight period.
Main adjustment to the near term forecast was to adjust PoPs based
on radar trends, and adjusted hourly temps based on cooler observed
early this evening.
An abnormally deep upper level low over the TN Valley early this
evening will drift south-southeast to a position along the AL/GA
border sw of ATL by Monday morning. The steady stream of moisture
ahead of this system that has been riding over the higher terrain of
eastern TN/western NC will also re-aligned its orientation with the
low`s movement, and extended from coastal SC into the western
Piedmont of NC on Monday. Strengthening sly flow in the 925-850mb
layer will tap a moist rich air mass residing over coastal
GA/southern SC with precipitable water values of 1.5 inches. The
increasing isentropic upglide and increasing divergence aloft will
lift this moisture, resulting in widespread showers and associated
light-moderate rainfall rates. Potential for heavier rainfall rates
to develop very late tonight/early Monday morning as low level
convergence increases and convective elements from SC drift into our
Hourly rainfall rates this evening will vary between a tenth of an
inch where light rain is occurring, to a quarter of an inch or a
little more where heavier showers occur. Expect the higher rain
rates to develop after 06Z in the western Piedmont and linger into
early Monday morning. The rain so far has primed the pump,
saturating the top soil. The enhanced rainfall rates later tonight
should quickly run-off, filling creeks and streams, leading to
increased flooding potential of creeks, streams, low lying areas
prior to daybreak across the western Piedmont, including the Triad
region. Expect additional rainfall amounts of 1-1.5 inches across
the western half of central NC overnight, and a half inch or less
across the eastern half.
On Monday, it now appears the focus for prolonged moderate-heavy
rain will shift to our southern counties as the low level flow
continues to back in response to the deep low drifting east across
GA. Strong low level easterly flow will set-up across our southern
counties by Monday afternoon-early evening. Low-mid level confluence
coupled with persistent upper divergence will maintain strong lift
of the moisture rich air mass, resulting in widespread showers and
isolated storms. Expect the northern extent of the widespread
moderate-heavy showers to remain just south of the Triad, though
reach up toward the Triangle area, with coverage expected to taper
off to the north-northeast of Raleigh. Additional rainfall amounts
of 1-2 inches highly probable across our southern counties with
another half to one inch probable across the north.
The approach of a sfc low up the SC coast Monday afternoon, may
spread an unstable air mass into our southeast counties, roughly
east of a Laurinburg-Goldsboro line. Strong kinematics coupled with
a slightly unstable, sfc based air mass may support the development
of isolated strong/severe thunderstorms with the main severe weather
threats strong/damaging wind gusts or a weak tornado. At this time,
the probability of occurrence appears low/weak.
High temperatures Monday dependent upon the extend of shower
coverage and whether the warmer air residing offshore is able to be
advected inland in to our southeast counties. Forecast high temps
should vary from the mid-upper 50s nw half to 65-70 far southeast.
.SHORT TERM /TUESDAY AND TUESDAY NIGHT/...
-- Changed Discussion --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.
-- End Changed Discussion --
.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --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.
-- End Changed Discussion --
.AVIATION /06Z Monday through Friday/...
As of 230 AM Monday...
24-hr TAF Period: Adverse aviation conditions in the form of
IFR/LIFR ceilings and rain are expected through the TAF period as a
potent upper level low and attendant surface low track southeast
from the Deep South to the Southeast coast. Elevated showers and
thunderstorms /heavy rainfall/ will be possible at all terminals
late this morning through this afternoon. Northeast winds initially
at 5-10 kt will increase to 10-15 knots with gusts to 20-23 knots
after sunrise. The FAY terminal could see light/variable or
southeast winds along with improved ceilings (MVFR or possibly VFR)
for several hours this afternoon, depending on the precise track of
the aforementioned surface low as it progresses toward the Southeast
Looking Ahead: Adverse conditions are likely to persist in
association with a lingering CAD wedge over the area Tue/Tue night.
Ceilings are gradually expected to lift/scatter out to VFR during
the day Wednesday as the upper level low lifts northeast along the
Mid-Atlantic coast. -Vincent
As of 910 PM Sunday...
...A Flood Watch is in effect through 800 AM Tuesday...
The threat for flooding of creeks and small streams is expected to
increase late tonight into early Monday across the western Piedmont
including the Triad region as the ground saturates and the rainfall
becomes heavier. The threat for flooding along creeks and streams
expected to encompass the remainder of central NC Monday into
Minor river flooding will become more likely later Monday and could
linger into midweek. Based on our expected rainfall distribution at
this time, the Haw river would be particularly prone to minor
flooding above Lake Jordan, but any of the mainstem rivers could
reach minor flood stage, especially given just a bit more rain than
On a positive note, we were on the cusp of drought conditions due to
rainfall deficits over the late winter and spring, so this event
will turn that around and possibly eliminate much of a drought
threat for the rest of the spring season.
Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043-