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Area forecast discussion 
National Weather Service Sioux Falls South Dakota
333 PM CDT Friday Sep 4 2015

Short term...(this evening through saturday)
issued at 333 PM CDT Friday Sep 4 2015

Band of elevated showers and thunderstorms near our eastern border
associated with a passing upper wave will continue to slide off to
the northeast and exit the area by early evening. Additional
isolated to scattered thunderstorms behind this line will likely
also continue to develop in the unsettled airmass where some
convergence has developed. This activity will be more spotty and
mainly focused east of i29.

With the upper wave lifting away from the region...a break in the
activity is expected late this evening through early morning. The
next wave approaches from the southwest Saturday morning and noses
into south central South Dakota late Saturday afternoon. Middle level thermal
boundary lifts into the Missouri Valley late tonight. With the low
level jet increasing in the area...some isolated showers and storms
will again be possible west of the James River. Chances steadily
increase in this area into the heat of the day as the wave
nears...but overall support is not especially organized on Saturday.
Think that scattered thunderstorms mainly across our western half is
the best bet for now. Precipitable water values remain seasonally
high...but the highest values will be in our east where activity
will hold off. Still think that heavy rainfall will be a concern for
any storms that do form in the afternoon. Shear in the afternoon is
quite meager but elevated instability does exist. Do not think that
severe weather will be much of concern...but an isolated marginally
severe storm may be possible.

Long term...(saturday night through friday)
issued at 333 PM CDT Friday Sep 4 2015

Tough call on probability of precipitation Saturday night into Sunday. Atmosphere is primed
for the potential for heavy rainfall event with precipitable water values in the
1.8-2" range...which is near the maximum of the moving range. Upper
wave is lifting to the northeast east...and the crux of the forcing
remains focused to the north and west of the forecast area. Corfidi
vectors across the area are weak...which suggests the potential for
slow moving and training of storms. With the uncertainty of
precipitation...kept probability of precipitation in the high change to low likely range...but if
something is able to get going...potential for heavy rain is high.

Front is a relatively slow mover across the area...so kept lingering
probability of precipitation across the eastern half of the forecast area on Sunday.

Much more seasonal conditions are expected next week with fairly
zonal flow aloft. There are a few embedded waves and have a few
sporadic chances of rain on Tuesday and Wednesday night...but
otherwise mainly dry conditions should prevail. With the passage of
the front Wednesday night...markedly cooler temperatures are
expected to surge into the plains. Have nudged highs down ever so
slightly on days 6 and 7 compared to guidance...close to 850 hpa
mixout.

&&

Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1244 PM CDT Friday Sep 4 2015

Generally VFR conditions are expected through the taf period. A
band of showers and storms near the i29 corridor will continue to
lift northeast through middle afternoon before exiting the region.
Some clearing will be seen behind the storms...however these high
base storms should keep ceilings and visibility in the vrf range.
Late tonight into Saturday morning...isolated to scattered high
based showers and storms will again be possible mainly across
south central South Dakota. Coverage will be too low to mention in the khon
taf at this time.



&&

Fsd watches/warnings/advisories...
South Dakota...none.
Minnesota...none.
Iowa...none.
NE...none.
&&

$$

Short term...
long term...
aviation...

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