Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 232324

Area Forecast Discussion
National Weather Service Sioux Falls SD
624 PM CDT Wed Aug 23 2017

.SHORT TERM...(This evening through Thursday)
Issued at 351 PM CDT Wed Aug 23 2017

A few showers associated with a subtle bit of forcing and some mid
level moisture are possible tonight across southwest Minnesota and
northwest Iowa. Instability is quite limited, so will leave mentions
of thunder out of the forecast. After overperforming in many spots
last night despite the calm conditions, tonight`s lows look to be
warmer due to an expected 5 to 10 knot southeast breeze.

Biggest forecast problem tomorrow will be the chance for showers and
storms Thursday afternoon. Forecast area will be under the favorable
region for ascent in relation to an upper level jet centered roughly
along an axis from the Twin Cities to Indianapolis. At the same
time, a weak impulse will swing across northern Nebraska, bringing
some additional forcing to areas along the Missouri River. Have
accordingly kept some chance PoPs in that area before 00z Friday.

.LONG TERM...(Thursday night through Wednesday)
Issued at 351 PM CDT Wed Aug 23 2017

Strong moisture advection in the 700-800 mb layer may lead to
scattered showers and thunderstorms Thursday evening mainly south of
I-90.  This activity is expected to expand across the eastern half of
the forecast area through the overnight hours Thursday night into
Friday morning.

Friday is conditionally unstable as temperatures warm above 70
degrees, especially west of I-29 where the cap is weaker.  Have
lowered forecast highs on Friday with abundant cloud cover expected
ahead of a series of short waves through the weekend.  The first
wave is expected to pass to the south of the region, but still
result in elevated showers and thunderstorms across the region.
Effective shear is weak, so am not anticipating severe weather, but
storms could temporarily pulse up with 1000-2000 J/kg of elevated
CAPE. Then on Saturday a second wave tracks from west to east across
South Dakota. Expect showers and embedded thunderstorms throughout
much of the day on Saturday, gradually decreasing Saturday evening
between disturbances.  On Sunday, another wave is expected to pivot
through the eastern portions of the forecast area.  Elevated
inversion will likely keep much of southeastern South Dakota dry,
while there is a chance for showers and thunderstorms across
portions of southwest Minnesota into northwest Iowa.

ECMWF hints that system will struggle to work far enough to the east
on Monday while the GFS is much more progressive.  Have left mention
of storms in forecast across northwest Iowa Monday afternoon for
potential of slowly evolving pattern.

Thereafter, conditions look to quiet down as surface ridge builds
into the Upper Midwest. Temperatures through the period remain cool,
generally 5-10 degrees below normal.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 621 PM CDT Wed Aug 23 2017

Strong warm advection signal combined with a minor shortwave may
keep scattered showers and isolated thunderstorms persisting well
into the overnight hours. Thin layer of instability aloft will be
enough to warrant thunder potential in most areas.  Generally
feel this precipitation axis will slide to the east as the
overnight moves on, but will maintain a scattered mid- level deck
into Thursday morning. Any aviation restrictions will be minor or
at least very limited in duration.

Thursday itself should be dry with a light wind and VFR




SHORT TERM...Ferguson
AVIATION...Dux is the U.S. government's official web portal to all federal, state and local government web resources and services.