Area Forecast Discussion
Issued by NWS Raleigh/Durham, NC

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FXUS62 KRAH 261420
AFDRAH

Area Forecast Discussion
National Weather Service Raleigh NC
1020 AM EDT Sat May 26 2018

.SYNOPSIS...
High pressure centered over the western Atlantic will extend
westward across the Carolinas through Sunday. Deep southerly flow
between Subtropical Storm Alberto and high pressure over the western
Atlantic will transport tropical moisture north into the area late
Sunday night through mid to late week, resulting in periods of
moderate to to heavy rain.

&&

.NEAR TERM /THROUGH TONIGHT/...
As of 1020 AM Saturday...

Latest surface analysis shows a ridge of high pressure established
in the western Atlantic with a general south to southwesterly flow
across the Carolinas. Further aloft, a narrow ridge of high pressure
extends northwest from the subtropical Atlantic to near the Carolina
coast. Further west, a trough is noted from the Great Lakes region
south into the Tennessee Valley and then into the Gulf of Mexico to
near Alberto.

Given a deep layer southerly flow, the air mass across central NC
has become quite moist with PW values ranging between 1.7 and 1.9
inches. Low level moisture has also increased, resulting in the
development of fairly widespread stratus across the area. A well
defined short wave, located across the NC Foothills/western Piedmont
is generating an area of rain and rain showers that is moving
northeast and will spread rain across the western Piedmont and
Triad. After this transient feature moves across the area, more
typical diurnally forced convection is expected this afternoon and
evening with convection focused across the Piedmont and to a lesser
extent in the southeast near the sea breeze. With little sustainable
forcing, weak to moderate instability and limited shear, no severe
thunderstorms are expected but locally heavy rain is possible given
the high PW and slow storm motion.

Temperatures should range near normal, with highs settling in the
low to mid 80s afternoon, and lows remaining near 70 degrees
overnight into early Sunday morning. -Blaes
&&

.SHORT TERM /SUNDAY/...
As of 330 AM Saturday...

Sunday will provide a brief reprieve from the unsettled weather
pattern, as central North Carolina finds itself between a
frontal zone to the north and the developing tropical system
Alberto to the South. Temperatures will rise into the mid to
upper-80s during the afternoon, with a few stray showers/storms
possibly sneaking south of the VA/NC border, or east of the
Blue Ridge Mountains, as the frontal zone becomes more active
by late afternoon. Most areas will remain dry and under broken
skycover Sunday.


&&

.LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
As of 330 AM Saturday...

Following a weakness between a pair of prominent ridges over the
Central US and off the SE coast, Subtropical Storm Alberto is
forecast to track NNW, making landfall along the Mobile/Florida
Panhandle late Monday, and will proceed slowly north through the
Deep South and Tn Valley through midweek, before eventually becoming
absorbed by the westerlies as it lifts into the Ohio Valley and
Northeast US late Wednesday and into Thursday.

Deep southerly flow channeled between Alberto and ridging  off the
SE coast, will draw high-daily maximum PWATS of over 2.0" north into
the area starting late Sunday night and will reside over the area
through mid to late week. This anomalous moisture coupled with s/w
disturbances embedded in the southerly flow aloft, along with
afternoon heating and resultant destabilization will set the stages
for periods of moderate to heavy rains across central NC Monday
through at least Wednesday. WPC`s new Day 3(Monday/Labor Day)
Excessive Rainfall Outlook, which only captures the beginning of the
expected wet-unsettled period, has the southeast two-thirds of the
forecast area in a slight risk for excessive rainfall(risk of
rainfall exceeding flash flood guidance), with the northern-
northwestern third in a marginal risk.

By Thursday-Friday, as Alberto`s remnants move off to the north,
it`s possible that the Carolinas could get dry slotted, which could
lower/limit convective coverage.

With soils already wet and streams and creeks elevated from recent
rainfall, additional heavy rain Monday through Wednesday will lead
to a threat of flash flooding across central North Carolina, with
river flooding possibly becoming a problem later in the week. This
flooding threat will likely necessitate the issuance of
a Flash Flood Watch in the next day or two. Residents that live in
flood prone or low-lying areas, should monitor the forecast closely.



Widespread clouds and rain will temper the heating with highs
generally 80 to 85 Monday through Wednesday. Potential for some
partial sun and stronger insolation could boost afternoon highs in
the 85 to 90 range. Balmy overnight lows in the upper 60s to lower
70s.

&&

.AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
As of 630 AM Saturday...

Through 12Z Sunday:  MVFR/IFR conditions due to low stratus will
slowly improve early Saturday morning, allowing CATs to slowly rise
back to VFR by mid day. This improvement will be quickly followed by
scattered shower and tstms development from late-morning through the
evening hours. Best coverage will likely be at KINT/KGSO during the
day, with TSRA struggling to push east into KRDU by the late
afternoon/evening hours. Flight conditions will locally lower to
MVFR/IFR in and around shower/tstms activity, but have settled on
tempo groups with timing uncertainties remaining. SW winds should
persist around 10kts mid morning Saturday with local gusts possible,
especially in the direct vicinity of thunderstorms. Any remaining
showers and storms should dissipate by nightfall, likely prior to
reaching KFAY/KRWI. Continued WAA regime and a moist boundary layer
should lead to additional stratus development overnight/early Sunday
morning, with intermittent VSBY drops also possible.

Looking beyond 12Z Sunday:  After a period of morning stratus, a
shower or storm will be possible across portions of the triad, which
could exhibit brief CAT drops. Widespread adverse aviation
conditions are expected Monday through Wednesday as widespread
showers and thunderstorms are expected.

&&

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

&&

$$
SYNOPSIS...CBL
NEAR TERM...Blaes
SHORT TERM...JM
LONG TERM...CBL
AVIATION...JM


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