Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 240113
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
910 PM EDT Sun Apr 23 2017

.SYNOPSIS...
A strong mid and upper level storm system will move slowly east
from the Tennessee Valley into the Carolina`s through Tuesday.
A surface low pressure will track from coastal Georgia to the Carolina
coast Monday through 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
region.

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 /Monday night through Tuesday/...
As of 330 PM Sunday...

The threat of flooding will continue with heavy rain gradually
tapering off from the west Monday night into Tuesday morning. The
severe threat should end as the low pressure and cold front shift
offshore early Tuesday. Rain will continue over much of the eastern
half of the region through at least mid day as the low tracks up the
coast.

Cloudiness and northerly low level flow will keep many areas in the
upper 50s and 60s Tuesday, with the warmest readings in the SW,
where some clearing may take place.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
As of 330 PM EDT Sunday...

A short wave ridge will quickly move across our region Tue Night
through Thu night, resulting in dry warming weather during this
time. Highs Wed and Thu in the 80s and lows in the upper 50s to
lower 60s.

A weak short wave in the sw flow is progged to move across the area
early Fri.  Will include a slight chance pop for daytime Fri.
Otherwise, the ridge over the se is progged to amplify over the
weekend, keeping the precip-makers to our north and west, and an
above normal airmass over our area.  Highs in the upper 80s and lows
in the mid 60s during this time.

&&

.AVIATION /00Z Monday through Friday/...
As of 825 PM Sunday...

Low end MVFR/IFR (to at times LIFR tonight) CIGS with MVFR/IFR VSBYS
in rain/drizzle and fog are expected through the TAF period. Periods
of heavy rain are expected across the area as a deep mid/upper level
low moves across the Deep South and Southeast U.S. The heavies rain
tonight is expected across western portions of the area, generally
KGSO/KINT, before shifting eastward on Monday into Monday night.
Isolated storms will be possible as well, primarily Monday
afternoon/evening at KFAY as the surface front may shift back
northward as a warm front. This may allow for a temporary return to
VFR cigs Monday afternoon/early evening at KFAY as well. The rain
should begin to taper to drizzle on Tuesday. However, low CIGS and
VSBYS below MVFR range should continue through 12z/Tuesday.

Cigs should rise gradually to MVFR areawide Tue as the mid level low
slowly departs the area, then trend to VFR Tue night lasting through
Fri with a drier air mass.

&&

.HYDROLOGY...
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
Monday night.

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
currently forecast.

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.

&&

.RAH WATCHES/WARNINGS/ADVISORIES...
Flood Watch through Tuesday morning for NCZ007>011-021>028-038>043-
073>078-083>086-088-089.

&&

$$

SYNOPSIS...Badgett
NEAR TERM...WSS
SHORT TERM...Badgett
LONG TERM...np
AVIATION...BSD
HYDROLOGY...WSS/MLM



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