Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 261239

Area Forecast Discussion
National Weather Service Columbia SC
839 AM EDT Sat May 26 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.


Upper trough to our west along the Miss valley extending south
into the GOMEX. Upper ridge to our SE off the SE coast. Embedded
short wave just to our north to push farther north, with some
slight upper height rises for our FA today. Slightly drier air
aloft today, but projected PW values still a respectably moist
1.8 inches. Scattered diurnal convective coverage anticipated.
Moderate instabilities provides an isolated severe threat.
Slightly lower PW may reduce localized heavy rain/flooding
threat slightly, but will still be possible with any slow
moving, training, or merging cells. Model blend on weather
elements looks good. Will expect diurnal decrease in convective
coverage this evening, with drier air moving in tonight.


Subtropical storm Alberto is expected to be located somewhere
in the central Gulf of Mexico at 12z Sunday with a somewhat
drier airmass over the forecast area and precipitable water
values at or below 1.5 inches. Though there are still some
differences among models in the track of Alberto there is
reasonable agreement it will stay well to the west of our area
so a wind threat is not expected. However, atmospheric moisture
will surge over the forecast area by Sunday afternoon and
evening as a plume of tropical moisture moves northward on the
eastern side of the system.

Precipitable water values rise well over 2 inches by 00z Monday
across the region with increasing moisture transport into the
area and widespread rainfall expected late Sunday and continuing
through Monday night. This will bring the potential for flash
flooding to the region given the generally wet pattern we have
been in for the past week or so and saturated soils, especially
in the CSRA where precipitation has been 300-600 percent of
normal. A flash flood watch may be needed. Severe weather
potential looks minimal, especially on Sunday due to drier air
in place and marginal instability. Forecast soundings indicate a
moist adiabatic profile Sunday night through Monday night so
think flooding from heavy rain remains the primary concern. WPC
has outlooked the area in a slight risk of excessive rainfall.

Temperatures this period will be near normal for highs in the
mid 80s and above normal for lows in the upper 60s to lower 70s.


Active weather continues through the extended forecast period
with abundant moisture in place and remnants of Alberto and
upper trough to the west early in the period then shifting
northeastward with the upper trough crossing the region late in
the week.

The remnants of Alberto are expected to be somewhere along the
central Gulf Coast states on Tuesday then moving northward into
the Tennessee Valley by 12z Wednesday. While the forecast area
will be relatively displaced from Alberto, significant moisture
will remain over the region with precipitable water values near
maximum values for this time of year. Will continue to carry
high chance to likely pops, primarily diurnally driven, through
the extended forecast Tue- Thu. The deeper moisture will finally
shift east of the forecast area by Friday but enough moisture
will remain combining with shortwave energy diving through the
upper trough to provide the chance for showers and
thunderstorms. High temperatures during this period will be near
normal to above normal, in the mid to upper 80s Tue-Wed and
upper 80s to around 90 Thu-Fri, and above normal for lows, in
the upper 60s to lower 70s.


Widespread LIFR to IFR CIGs this morning, with a return to VFR
expected by late morning. Will expect scattered mainly afternoon
and evening showers and thunderstorms, diminishing by early
tonight. Will handle with VCSH and tempo SHRA for now. Lowering
CIGs/VSBYs expected again late Sat nt into Sun morning.

EXTENDED AVIATION OUTLOOK...Late night and early morning IFR to
MVFR ceilings and visibilities along with mainly diurnal
showers and thunderstorms through the middle of next week as a
very moist air mass remains over the region.




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