Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 120010

Area Forecast Discussion
National Weather Service Sioux Falls SD
710 PM CDT Fri Aug 11 2017

.SHORT TERM...(This evening through Saturday)
Issued at 257 PM CDT Fri Aug 11 2017

We`re watching a pair of waves expected to impact the area tonight
and Saturday. A fairly weak shortwave feature currently located near
the MT/WY/SD border, will split as it tracks east, with the main
forcing tracking into the highway 14 corridor late tonight into
Saturday, while the secondary bit of energy passes south of the

A few spotty showers will remain possible this afternoon where the
diurnally driven cumulus field is a bit more robust to the north of
I-90. This activity will be very light and should quickly diminish
later this afternoon. The shortwave approaches late tonight, with
isolated to scattered showers and a few rumbles of thunder moving
into south central SD by sunrise. Showers and storms will spread
into southeast SD and southwest MN in the afternoon. Instability
remains very meager at less than 200 j/kg with poor mid level lapse
rates, so think that thunderstorms will be pretty spotty. Expect
more hit or miss type showery conditions. With the main forcing
moving through the highway 14 corridor and across Nebraska, will
leave out pops for far southeast SD and northwest Iowa through
Saturday afternoon. Best chances to see measurable rainfall will be
south central SD through the highway 14 corridor, and even here it
should not be a total wash-out. Temperatures will remain seasonally
cool, with highs in the 70s.

.LONG TERM...(Saturday night through Friday)
Issued at 257 PM CDT Fri Aug 11 2017

Saturday night into Sunday will see a pretty good chance for showers
and thunderstorms, but at this time instability is pretty marginal
so not anticipating any severe weather. Shear is a little more
organized in central parts of SD but forecast instability too low to
worry about at this time. If instability can creep up to 1500 J/kj
or higher the relatively decent shear would support a few severe
storms. The better chances for rain should exit sometime Sunday
afternoon as the dry slot settles in. Temperatures will remain a bit
on the cool side Saturday night into Sunday with a cooler air mass
and clouds to contend with. Lows will be in the 50s with highs in
the lower to mid 70s.

Overall temperatures will remain seasonally cooler Monday through
Friday, but will be closer to normal much of the week. Upper level
flow should be fairly weak with a bit of an omega block in place
through the period. A couple of weak waves moving through the ridge
will keep this ridge from creating dry and hot conditions. The upper
level trough to the west should break down the weak ridging in place
by mid week. While the chances for showers and thunderstorms will be
fairly low, the better chance will be Tuesday night into Wednesday
as the main trough spreads across the Northern and Central Plains. A
quick glance through the model soundings do not indicate any
concerns with severe weather during this time.


.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 710 PM CDT Fri Aug 11 2017

Isolated afternoon showers will continue to dissipate through 02Z.
Focus then turns to increasing chance of scattered showers moving
into areas west of I-29 after 12/08Z. This activity, which should
be primarily showers with just isolated thunder, expected to move
east through Saturday, largely impacting areas along/north of
I-90, including KHON/KFSD through Saturday afternoon. Relatively
dry lower levels should allow VFR conditions to prevail through
the period.




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