Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 270822
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
422 AM EDT Sun May 27 2018

.SYNOPSIS...
Tropical moisture will stream north into our region from the
south late today and tonight. Heavy rain possible. Expect a
moist pattern to remain through late week.

&&

.NEAR TERM /THROUGH TONIGHT/...
Temporarily tranquil across the forecast area (FA) currently.
Upper trough remains to our west along the Miss valley extending
south into the GOMEX, with an upper ridge to our SE off the SE
coast. Surface high offshore, with center of subtropical storm
Alberto currently over the SE GOMEX. Alberto is forecast to
shift to the NNW up through the E GOMEX through tonight. Models
indicate upper short wave energy and batch of tropical moisture
to our south will shift north into our FA late today and
tonight. Projected precipitable water (PW) values are a very
high 2.1 - 2.3 inches, about 175% of normal. Satellite indicates
a veil of upper level cloudiness will continue to stream north
into the FA, cutting down on insolation/max temps some. Latest
high resolution models indicate scattered convection possible
this afternoon, but main batch of precipitation expected to
shift into the S FA late this afternoon and continue to shift
north overspreading the FA tonight. Guidance suggesting a
widespread areal average of 1 to 2 inches of rain across the FA
will fall in about an 8 to 12 hour period, with expectation of
higher local amounts possible. Considering recent heavy rains,
especially CSRA and west Midlands, where rainfall amounts
during the past week have been 400-600% of normal, provides
concern for flash flooding. Additional concerns involve
increased outdoor activities given holiday weekend, and timing
of rain at night making it more dangerous. After coordination
with surrounding offices, issued a flash flood watch for the
entire FA from 00-12Z. Weak to moderate instability, plus some
shear associated with proximity of circulation of Alberto, could
possibly provide an isolated weak tornado threat tonight as
well.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Alberto is forecast to be located over the far northern Gulf of
Mexico just south of the Florida panhandle coast at 12z Monday.
Models are in pretty good agreement with the track of Alberto
and also showing a dry slot wrapping around the system and
pushing northward into the forecast area on Monday. Expecting
widespread rain associated with the initial surge of tropical
moisture to be over the northern part of the forecast area and
shifting northward through the day Monday with mainly scattered
showers prevailing during the afternoon into Monday night as the
dry slot overspreads the forecast area.

The remnants of Alberto are forecast to lift northward into the
Tennessee Valley Tuesday and eventually into the Ohio Valley.
The forecast area will be in the right quadrant of the
circulation on Monday and Tuesday so cannot totally rule out the
possibility of isolated brief, weak tornadoes, though it does
not appear to be the significant threat. SPC has outlooked parts
of the forecast area in a marginal risk on Monday and Tuesday.
Heavy rain will continue to be the primary threat during this
period with precipitable water values remaining at or above 2
inches. WPC continues to advertise a slight risk of excessive
rainfall over the forecast area Monday and Monday night.

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

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
Active weather will continue during this period along with a
warming trend into the weekend to above normal temperatures.

The remnants of Alberto will continue to lift northward into the
Great Lakes region by Wednesday night and become absorbed into an
upper trough moving across southern Canada.  Weak upper troughing
will remain across the southeast and Mid-Atlantic states through the
week but then another upper trough will dive southward along the
east coast on Saturday. Thinking that chances of rain will become
more diurnally driven during this period and diminish late in the
week by Friday as some drier air works into the region as 500mb
heights become more northwesterly and shifts the deeper moisture to
our east.  Near normal high temperatures expected early in the
extended forecast period, but as the atmosphere dries out a bit
later in the period, temperatures are expected to rise above normal
with highs pushing into the 90s Fri/Sat. Overnight lows expected to
be well above normal the entire period in the lower 70s.

&&

.AVIATION /08Z SUNDAY THROUGH THURSDAY/...
VFR currently, at 08Z. A moist SE low level flow provides
expectation of some stratus developing later tonight. Latest
model guidance not hitting it particularly hard and there was
less rain coverage the previous afternoon/evening. Veil of high
level cloudiness and a 20 kt low level jet reduces fog
potential, except for fog prone sites AGS and possibly OGB. For
now, will indicate tempo IFR CIGs at all TAF sites, with some BR
at fog prone AGS/OGB.

Otherwise,  expect VFR through much of today. Scattered
convection possible this afternoon, and will handle with VCSH
for now, but main story will be potential for widespread heavy
rain shifting north into the forecast area from the south late
today and tonight. Thunder potential exists but for now will
indicate predominate SHRA, with tempo +SHRA, and MVFR CIGs, late
in the TAF period.

EXTENDED AVIATION OUTLOOK... A moist atmosphere is expected to
remain in place, providing of late night and morning IFR to MVFR
ceilings and possibly visibilities, along with mainly diurnal
showers and thunderstorms through the period.

&&

.CAE WATCHES/WARNINGS/ADVISORIES...
GA...Flash Flood Watch from this evening through Monday morning for
     GAZ040-063>065-077.
SC...Flash Flood Watch from this evening through Monday morning for
     SCZ015-016-018-020>022-025>031-035>038-041.

&&

$$


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