Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 231808
AFDCAE

Area Forecast Discussion
National Weather Service Columbia SC
208 PM EDT Tue May 23 2017

.SYNOPSIS...
Several waves of low pressure moving along a frontal boundary
stalled near the forecast area will bring periods of showers and
thunderstorms to the region through Wednesday. The cold front
will finally be moving east of the region Wednesday night,
with drier and cooler air taking hold by the end of the week.

&&

.NEAR TERM /THROUGH TONIGHT/...
A closed low over the upper Mississippi Valley will amplify
today as a pair of short waves rotate through the base of the
trough. A surface front has stalled across the forecast area
and the first wave is currently moving through with light to
moderate rain showers. The Flash Flood Watch remains in effect
due to the increased threat for heavy rain associated with this
front and anomalously high precipitable water near 2 inches.
Thunderstorms have begun to develop to the south where breaks in
cloud cover allowed daytime heating to destabilize the
atmosphere.

A second stronger shortwave currently over southern Georgia
will lift up into the area this evening, and thunderstorm
potential will increase. A few of these storms may become severe
with damaging winds and perhaps an isolated tornado. SPC has
issued a slight risk of severe thunderstorms for the south
Midlands and CSRA due to a strengthening low-level jet that
will peak around 55 kts, and storm relative helicity that
exceeds 300 m2/s2. Yet the main threat remains heavy rain due
to training of storms, and WPC has portions of the region in a
slight risk of excessive rainfall.

Most of the rain should move out of the area tonight, as the
short waves move to the north and east. However, abundant low-
level moisture will persist, and fog and low stratus with
drizzle will be likely going into Wednesday morning. Abundant
moisture and clouds will hold overnight lows in the mid 60s.

&&

.SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/...
An upper level low will move southeast over the mid-Mississippi
Valley Wednesday while a trough of low pressure rotates around
the upper low across the southeast U.S.  This will result in
strengthening mid-level flow across the region. Moderate
instability combined with strengthening wind fields and a moist
air mass ahead of an approaching cold front will result in a
favorable environment for severe storms especially later in the
day. Flash flood threat over much of the area continues so a
flash flood watch remains in effect until Wednesday evening.

The chance for showers and thunderstorms is expected to diminish
Wednesday evening as the cold front moves east of the Midlands
and CSRA.

For the most part used guidance consensus for temperatures with
highs mostly in the 70s and lows mostly in the lower 60s.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
The front should be east of the area Thursday, but with cold
temperatures aloft the area may still see a few showers through
the afternoon. Drier and cooler air should then spread over the
region for the end of the week but warming again by weekend. A
front to the north may move south into the area late in the
weekend resulting in widely scattered afternoon convection. The
front may linger into the early part of the work week with a
threat of precipitation each day. Highs will be mostly in the
80s and lows around 70 each day.

&&

.AVIATION /18Z TUESDAY THROUGH SATURDAY/...
Restrictions expected through the TAF period.

A very moist atmosphere, combined with a stalled front, and
several waves along the front, are combining to produce
widespread showers with light to moderate rain. This is causing
variable ceilings and visibilities that are generally MVFR, but
could become IFR in heavier rain. The potential also exits for
more significant shower and thunderstorm activity this
afternoon and evening. Showers will move away from the area
after 02Z tonight, but fog and low stratus are likely given
abundant low-level moisture. The next wave of moderate rain
will arrive mid-morning Wed and persist through Wednesday
evening.

EXTENDED AVIATION OUTLOOK...Precipitation and restrictions expected
into Wednesday night. Showers and breezy conditions possible
Thursday. Much drier with a return to VFR conditions by Friday.

&&

.HYDROLOGY...
With additional rainfall expected today, the ground will become
increasingly saturated. This will result in flooding potential
increasing through Wednesday. Given heavy rain also across the
upstate, will see rises in rivers and streams during the next
24-36 hrs, with moderate rises expected on the area rivers.
This could lead to river flooding and will be monitored
closely.

&&

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

&&

$$



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