Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 130405

Area Forecast Discussion
National Weather Service Sioux Falls SD
1105 PM CDT Sat Aug 12 2017

.SHORT TERM...(This evening through Sunday)
Issued at 316 PM CDT Sat Aug 12 2017

At 2 pm this afternoon isolated thunderstorms continued between
Huron and Pierre where then have meandered for much of the day. The
latest water vapor loops show a nice wave across North Dakota with a
moderate jet max wrapping around the south side of this low
pressure. The stronger EML was just moving into western SD with a
nice dry slot poking into northwest South Dakota. As this upper
level support moves farther out onto the Plains it should interact
with some moderately unstable air in central and western parts of
South Dakota. Strong to severe thunderstorms will likely develop in
those areas by mid to late afternoon and could push into areas west
of the James River by about 6 to 7 pm. At this time the instability
to the east of the Missouri River drops off quickly which should
keep the severe threat west of the Missouri River. Not out of the
question however to get a few severe storms into locations west of
the James River before 10 pm CDT. There will also be a threat for
some strong to lower end severe storms mid afternoon with daytime
heating near the Missouri River.

After 10 pm the small severe weather threat should be over and a
band of moderate showers with isolated thunderstorms will continue
to press east into east central SD, southwest MN and finally
northwest IA.

The threat for showers and thunderstorms will continue into Sunday
afternoon with the chances slowly ending from west to east. If
everything comes together tomorrow an isolated severe storm would be
possible in far east central SD, southwest MN and northwest IA but
for now that threat is a little too low to be concerned about right

.LONG TERM...(Sunday night through Saturday)
Issued at 316 PM CDT Sat Aug 12 2017

Slow moving upper level trough exits the region Sunday night.
Ongoing scattered shower and thunderstorm activity across the bulk
of the area will diminish from west to east overnight. Isolated to
scattered showers or thundershowers may linger into Monday morning
with a break in activity likely around midday. Not a great deal of
model agreement, but the GFS and NAM indicate that by late afternoon
or early evening, a warm front lifts northward into the Missouri
Valley then north of I-90 overnight. The CMC and ECMWF are far less
bullish with this activity. Will go with scattered showers and
thunderstorms lifting northward into Iowa and southeast SD in the
evening and into SW Minnesota late, but confidence remains somewhat
low with the uncertainty of how quickly the front lifts northward.

Potent trough begins pushing into the northern High Plains on
Tuesday, however there remains some timing differences in how
quickly a wave lifts into the eastern Dakotas. The CMC remains the
slowest model and is something of an outlier. Scattered showers and
thunderstorms will remain possible through the day Tuesday. Went
ahead and boosted pops into the 60 to 80 percent range on Tuesday
night, with most models bringing the potent wave into the region
around this time. Scattered showers and storms remain possible into
Wednesday morning, but will begin to taper off through  Precipitable
water values are pretty hefty, with model QPF values pretty high.
Areas that do see thunderstorms could see some decent rainfall
amounts. But as is typical with convection, not every location will
see significant rainfall.

Models diverge even further late in the week, although it does look
like the active weather pattern continues. Not enough confidence in
any one solution, but it does look like a wave rolls across the
northern Plains around the Friday or Friday night time frame.
Temperatures remain slightly below normal through the extended


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1100 PM CDT Sat Aug 12 2017

Scattered rain chances will continue across the region tonight
and Sunday. VFR conditions will be prevalent to start the period,
but increasing low level moisture will lead to a period of MVFR-
IFR ceilings, primarily along/north of I-90 corridor 12Z-18Z,
which will impact KHON/KFSD TAF locations. Conditions will improve
again after 18Z.

Thunder threat is isolated due to limited instability, so will
have minimal mention of thunder in the TAFs at this point.




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