Flooding in South Dakota, September 1 to 30, 2018

Area Forecast Discussion
National Weather Service Sioux Falls SD
1029 PM CDT Fri Aug 31 2018

.UPDATE...
Issued at 711 PM CDT Fri Aug 31 2018

With capped atmosphere, and a lack of trigger, have continued to
trend down on Pops through the overnight hours. Expect focus this
evening to be towards the highway 30 corridor closer to short wave
train and convergence of the nose of the low level jet. With the
low level jet oriented southwest to northeast, expect the bulk of
the storms to be focused to the south and east of the forecast
area.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 347 PM CDT Fri Aug 31 2018

Low cloud decks continue to clear across the region, with
temperatures quickly reaching around 80 degrees for afternoon highs.
The main forecast concern over the next 24 hours will be with
location and timing of thunderstorms. Currently, high-resolution
models highlight areas northeast of a Brookings, SD to Luverne, MN
line as having the best chance for storms breaking the capping
inversion. Current satellite and radar imagery show support for this
forecast, with surface-based storms already initiating in far
northeast SD. These are forecast to move southeastward over time.
Hail and gusty winds would be possible under the stronger cells this
evening. As the southwesterly low level jet increases around sunset,
models indicate moisture transport in the 850 hPa layer removing the
cap in central IA, creating a secondary focus for storm activity.
Thunderstorms in this region develop to the north and west during
the early overnight, eventually impacting northwest IA up to the
state line with MN. CAPE over 1000 J/kg would keep hail as a
threat despite the elevated nature of these storms. Northwest IA
will see this scattered storm threat last throughout the
overnight.

The nearly stationary front that is serving as a focus mechanism for
storms will slowly move to the southeast during the day Saturday,
lowering the chance of storms during the day. This boundary moves
back to the northwest Saturday night, slowly increasing the chances
for showers and thunderstorms into Sunday.

.LONG TERM...(Saturday night through Friday)
Issued at 347 PM CDT Fri Aug 31 2018

The large-scale pattern changes little over the next 7 days, with
active weather and daily chances for thunderstorms. Daily high
temperatures range from the mid 70s to low 80s each day, with lows
in the 60s.

The two best periods for widespread thunderstorms and localized
heavy rain look to be Sunday night into Monday, and then again on
Tuesday night into Wednesday. Both of these periods will have
enhanced lift thanks to a couple upper level shortwaves moving
through the southwesterly sub-tropical jet stream aloft. Moisture
transport in the southerly surface flow ahead of these waves will
bring PWATs into the 1.5 to 2.0 inch range, supporting high rainfall
rates with thunderstorms. Mean storm motion looks to favor storms
moving along boundaries, which would encourage training storms. The
details for this treat are still hazy, given a lack of high
resolution guidance at this time range, but these will both be time
frames to focus on over the next several days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1028 PM CDT Fri Aug 31 2018

The thunderstorm threat has diminished for the overnight hours.
Otherwise, guidance is suggesting MVFR/IFR stratus to develop in
areas roughly from the I-29 corridor and eastward later tonight
into Saturday morning. With winds dropping off later tonight, may
see locally reduced visibilities in patchy fog.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

UPDATE...BT
SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...JM

Hazardous Weather Outlook
National Weather Service Sioux Falls SD
1053 PM CDT Fri Aug 31 2018

IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097-
098-NEZ013-014-SDZ038>040-050-052>071-020400-
Lyon IA-Osceola-Dickinson-Sioux-O'Brien-Clay IA-Plymouth-Cherokee-
Buena Vista-Woodbury-Ida-Lincoln MN-Lyon MN-Murray-Cottonwood-
Nobles-Jackson-Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-
Brookings-Gregory-Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-
Davison-Hanson-McCook-Minnehaha-Charles Mix-Douglas-Hutchinson-
Turner-Lincoln SD-Bon Homme-Yankton-Clay SD-Union-
1053 PM CDT Fri Aug 31 2018

This Hazardous Weather Outlook is for portions of northwest Iowa,
west central Iowa, southwest Minnesota, northeast Nebraska,
central South Dakota, east central South Dakota, south central
South Dakota, and southeast South Dakota.

.DAY ONE...Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Saturday through Thursday

There is a chance of thunderstorms again for Sunday through the
end of next week. At this time, severe storms do not seem likely.
However, heavy rain is possible from Monday through Thursday,
mainly south of Interstate 90.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected.