Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 190911
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
411 AM CDT FRI AUG 19 2016

.SHORT TERM...(Today and Tonight)
Issued at 410 AM CDT Fri Aug 19 2016

Outflow reinforced frontal boundary has pushed completely through
the CWA by 08z. Large MCS pulling away across Minnesota as leading
wave in northern tier trough pulls away and modest low level jet
veers eastward, but main upper wave continues to dig southeast
across western Montana.  Progression of the complex upper trough and
defining hourly precipitation chances are a massive challenge today.

Scattered convection ongoing mainly in southwest Minnesota and
northwest Iowa on nose of southwesterly low level jet. This feature
will continue to weaken through early morning, so expect
precipitation to gradually become less defined across northwest Iowa
heading into early morning hours.  For the remainder of the morning,
precipitation chances will largely be defined by progression of MCV
out of north central Nebraska as it moves across southeast South
Dakota and into southwest/west central MN midday. While coverage of
precipitation with feature is fairly sparse at the current time,
CAMS and several larger scale solutions indicate this should change
over the next few hours into a cluster of showers and embedded
thunder. While area is post frontal, there is still 500-1000 J/kg
elevated instability, with fairly minimal capping if model profiles
are anywhere near reliable.  Larger scale forcing behind this wave
will become lacking for much of the later morning and afternoon
hours which should start to diminish precipitation back to the west
of I-29. Further eastward, there will be a continued trajectory of
elevated lift with Q vector convergence axis lingering parts of SW
MN into NW IA throughout much of the day, making it difficult to
fully drop precipitation chances at any time.  While clouds will be
fairly prevalent, loss of precipitation and the main cold surge tied
up with the secondary trough will give a window for temps to recover
somewhat today, mainly into the 70s.

At this point, it would appear that any appreciable severe weather
threat will be to the south/east of the FSD CWA, with perhaps a
marginally strong storm toward evening across areas southeast of a
KSPW to KSUX line, with shear and instability both likely less than
needed for organized storms.

Very dynamic system will drop southeast across the area tonight.
Short wavelength suggests a fairly effective lifting system, so look
for a cluster of showers and embedded thunder.  Overall, CAPE
associated with secondary area of approaching from the west during
the evening will be 300-500 J/kg at most, so thunder will be
secondary to the coverage of precipitation. Will push pops to likely
as area works across the CWA, with system actually much more cool
season-like in terms of working pops around frontogenesis and
looking into stability over the front. Appears as if precipitation
should remain a somewhat broad area along the mid level front as it
moves across the CWA.  A slower progression to clouds along with the
moisture present will allow temps to be just a little warmer than
earlier forecast.

.LONG TERM...(Saturday through Thursday)
Issued at 410 AM CDT Fri Aug 19 2016

Upper trough lingers over the northern and central Plains into
Saturday. The main shortwave exits to the east around daybreak,
however a trailing wave dips across the highway 14 corridor in the
afternoon. With the slower timing of the wave, have added scattered
showers with isolated thunder in the morning, while instability
developing in the warmth of the afternoon will likely keep scattered
to isolated showers going in the highway 14 corridor, southwest
Minnesota and the Iowa Great Lakes region through around sunset.
Stratocumulus will blanket the area in the morning, gradually
clearing in the evening through Saturday night.  Temperatures will
be quite a bit cooler than recent days, with highs only reaching the
upper 60s to lower or mid 70s.

Dry weather returns Saturday night through Monday night with cool
northwest flow gradually becoming replaced with a building ridge
over the high Plains. Temperatures moderate on Sunday, improving
around 5 degrees from Saturday, and return to the 80s and lower 90s
on Monday.

Models agrees in bringing a deep closed low across southwestern
Canada early next week and tracking it east along the US/Canadian
border. Southwest upper flow Tuesday and Wednesday and breezy
southerly winds will allow for some moisture return. Shortwave lifts
northeast around the Tuesday/Tuesday night time frame, however the
location of this wave is uncertain, with the ECMWF keeping it
largely south of the forecast area while the GFS and GEM bringing
through the region, albeit with slightly different timing. Think
that Tuesday night looks like the best chance, and therefore high
end chance pops are quite reasonable. Instability looks pretty good,
however shear in pretty meager during the day Tuesday, improving
into the evening hours.

Another front moves through the region and brings about another shot
of cooler temperatures Wednesday through Friday with highs mainly in
the 70s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1251 AM CDT Fri Aug 19 2016

Broad convective complex will continue to impact locations
generally north of a KMJQ to KYKN line through 19/08Z before
gradually weakening. In larger stratiform zone, will get
spotty/brief incursions of visibilities and ceilings into MVFR
category. Ceilings may become lower in postfrontal environment by
this evening with reinforcing push from upper trough, perhaps more
widespread MVFR conditions initiating toward 06z.


&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Chapman
LONG TERM...
AVIATION...Chapman



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