Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 251847

Area Forecast Discussion
National Weather Service Columbia SC
247 PM EDT Fri May 25 2018

The region will remain moist and unstable the next few days
between a ridge offshore and weak low pressure to the west.
Scattered to numerous showers and thunderstorms, mainly during
the afternoon and evening, are expected. Periods of heavy rain
are possible Sunday and Monday as a plume of tropical moisture
from Subtropical Storm Alberto is directed into the area.


Deep moist southerly flow across the area this afternoon with
high pressure at the surface and aloft off the coast and low
pressure to our west. Precipitable water values ranging from
1.8 to 2.0 inches with weak to moderate instability this
afternoon. Scattered to numerous showers with isolated
thunderstorms in progress. Isolated severe possible, but main
threat will again be locally heavy rain/flooding due to the high
moisture levels with any slow moving, merging or training
cells. Convection should diminish with loss of heating early

Early afternoon temperatures mid 70s to mid 80s are will on the
way to highs in the low to mid 80s. As with previous 2
nights...will see lows in the upper 60s to lower 70s.



Saturday, the moist airmass will remain over the FA through the
afternoon allowing mainly diurnal showers and thunderstorms to
develop. With the upper level ridge axis shifting east of the FA
there may be some weak upper level support for thunderstorms late in
the day. However 850 mb high pressure ridging into the area will
help keep coverage limited. Overall the chance for rain will be
lower than the past few days with a low threat of severe weather.
Although we cannot rule out the possibility of a severe storm with
slightly drier mid-level air in place and possible weak upper level

Saturday night should provide a brief break in the wet pattern. Mid
level drier air moves into the region and precipitable water values
drop to below 1.5 inches.

Highs will generally be in the mid to upper 80s with lows overnight
in the mid to upper 60s.



A surge of tropical moisture will move northward into the forecast
area Sunday afternoon or Sunday night. Strong moisture transport and
weak potential instability should yield widespread showers and some
thunderstorms along with a heavy rain threat through Monday. Flash
flooding may be possible, particularly in flood-prone areas and
where heavy rainfall in the past several days have saturated soils.
The CSRA and areas along and south of I-20 have received 2 to 5
inches of rain in the last seven days and may be more prone to flash
flooding. A flash flood watch may be needed.

The unsettled weather pattern is expected to continue through much
of the extended forecast period. Moderate to heavy rainfall may be
possible through the remainder of the long term, although confidence
is not high enough to include heavy rain in the forecast after
Tuesday. Mainly due to the possible track and intensity of
Subtropical Storm Alberto. Nevertheless, there is high confidence in
an abundantly moist airmass with precipitable water values around or
above 2 inches throughout the period with persistent southerly flow
off the Gulf of Mexico. There is at least a high chance of showers
and thunderstorms through Thursday.

High temperatures during this period will be near normal, in the mid
to upper 80s, and above normal for lows, in the upper 60s to lower


Showers with isolated thunderstorms will continue to cross the
TAF sites through the rest of the afternoon...producing
CIG/VSBY restrictions. Unstable and very moist atmosphere over
the region combined with heating and inland moving sea breeze
will keep convection through the afternoon. Convective coverage
expected to begin decreasing and shifting north this evening.
Models continue to indicate MVFR/IFR cigs developing overnight
given abundant low level moisture beneath the nocturnal
inversion. Fog development may be limited given a 15 to 20 knot
low level jet. Should see improving conditions by 26/15Z.
Convection not expected to be as widespread Saturday afternoon.

EXTENDED AVIATION OUTLOOK...Restrictions in late night and
early morning fog and stratus should develop Saturday night into
early Sunday morning. Tropical moisture associated with
Subtropical Storm Alberto will increase by the late Sunday into
Monday, increasing the frequency and intensity of showers and
associated restrictions.




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