Area Forecast Discussion
Issued by NWS Columbia, SC

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FXUS62 KCAE 231010

Area Forecast Discussion
National Weather Service Columbia SC
610 AM EDT Tue May 23 2017

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 for the end of the week.


Flash flood watch remains in effect due to an increased threat
for heavy rain associated with stalled frontal boundary and
anomalously high precipitable water. There is also a slight
risk of severe thunderstorms especially in the south Midlands
and CSRA associated with strengthening low level jet 30 to 40 kts
this morning and a weak meso-low tracking northeast this
afternoon along a frontal boundary.

A closes low over the upper Mississippi Valley will amplify
today as a short wave troughs rotate through the base of the
trough today and tonight. A surface front extending from CLT to
ATL will move into central SC and east central Georgia this
morning. The models suggest a surge of moisture with
precipitable water near 2 inches. Short wave trough moving
through the area along with a weak surface low/meso low should
lead to numerous showers and a few thunderstorms this morning
into the afternoon. A few of these storms may be
severe...especially south of the front in the south Midlands and
CSRA...with damaging winds and perhaps an isolated tornado.
Concern with enhanced 0-1 km SR Helicity southeast through the
afternoon. But the main threat remains heavy rain due to
training of storms near stalled front. WPC has region in slight
risk of excessive rainfall. There may be a lull late in the day
as stronger short waves move to the north and east.
However...air mass will be weakly to moderately unstable and
front remains in the area focusing low level convergence. The
front may move north to near the SC/NC border during the
overnight and convection should diminish somewhat as short waves
move to the northeast...but air mass remains moist and

Have indicated categorical pops today with high temperatures
ranging from the mid 70s west to around 80 east. Abundant
moisture and clouds will hold overnight lows in the mid 60s to
around 70.


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. Flash flood threat
continues along with slight risk for severe storms.

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

We used Mos guidance consensus used for temperatures with highs
ranging from the mid 70s to around 80 and lows in the upper 50s
to mid 60s.


The front should be east of the area Thursday, but with cold
temperatures aloft the area may still see isolated 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 isolated afternoon convection.


Restrictions expected through the TAF period. A slow moving
front, a moist atmosphere, some upper energy and a surface wave
will contribute to shower and thunderstorm activity.

Moist low levels resulting in stratus across the region currently
with mainly IFR CIGs. This is expected to continue in the near term,
with some diurnal improvement to MVFR later today outside any
convective activity. Current radar mosaic, and latest high
resolution models, suggest periods of light rain in the near
term, with more significant shower and thunderstorm activity,
and associated CIG/VSBY restrictions, expected at times later
today generally from mid to late morning through much of the
afternoon. A relative lull in the precipitation is expected
tonight, before the next wave of rain Wed/Wed nt. Rain cooled
air along with additional diurnal cooling expected to result in
lowering CIGs tonight, and possibly some reductions in VSBYs.

EXTENDED AVIATION OUTLOOK...Precipitation and restrictions expected
Wed/Wed nt. Breezy conditions possible Thursday.


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 also see rises in rivers and stream during the
next 24-36 hrs with moderate rises expected on the area rivers.
This may lead to river flooding and will be monitored closely.


GA...Flash Flood Watch through Wednesday evening for GAZ040-063>065-
SC...Flash Flood Watch through Wednesday evening for SCZ015-016-018-


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