Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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805
FXUS63 KFSD 232017
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
317 PM CDT SAT JUL 23 2016

.SHORT TERM...(This evening through Sunday)
Issued at 316 PM CDT Sat Jul 23 2016

Focus will be on the possibility of storms firing within the next
few hours ahead of an advancing cold front. Shortwave located over
northeast South Dakota and Southeast North Dakota is tracking east
with a trailing front moving into south central South Dakota through
mid afternoon. Expect the main focus of thunderstorm activity to be
focused near the shortwave energy, extending along a convergence
zone in northeast SD and east central MN this afternoon and early
evening, then track east to southeast.

The question will be how far south the convection will build into
our forecast area. The CAMs keep the vast majority of the forecast
area dry, skirting the storms outside our area. The NAM, ECMWF, and
to a lesser extent the GEM, however, support the idea that storms
will pass through our northern and eastern counties. If storms do
manage to increase to our north, these models suggest that
thunderstorms may congeal into an MCS this evening, potentially
impacting the highway 14 corridor, southwest Minnesota, and Iowa
Great Lakes region through late evening. With spotty storms already
firing along the axis of greatest instability in northeast SD and
west central MN, and increasing instability and good shear in
southwest MN, did up storm chances in the aforementioned areas. The
main severe threats will be wind gusts to 70 mph, with a lesser
threat of large hail up to half dollars. Elsewhere in the forecast
area, shear is weaker and strong capping remains. With the better
dynamics well north of the area, storm development is less likely.

Cooler temperatures and lower dewpoints arrive behind the front,
bringing a nice reprieve from the recent heat. Skies will be mostly
clear to partly cloudy on Sunday with cooler high temperatures in
the 80s.


.LONG TERM...(Sunday night through Saturday)
Issued at 316 PM CDT Sat Jul 23 2016

Sunday night and Monday still look dry and mild. Enough return of
instability and moisture to produce storms along the Missouri River
seems highly unlikely as the low level and upper ridge moves across
our area to the north. Lows Sunday night will be 60 to 65 and highs
Monday should be a fairly dry mid 80s to lower 90s.

The passage of the low and upper level ridges and the transition of
the flow aloft to westerly and subject to passage of weak waves
will bring enough moisture and instability to return a threat of
showers and storms for a few days starting Monday night and
Tuesday.temperatures will remain generally mild with just warming
of nighttime readings. In fact, as the flow gradually becomes west
northwesterly later in the week, a little cooling is likely. Fairly
modest MUCAPE values of 1000-3000 J/kg as projected by the GFS seem
to indicate the severe threat is low. Action of a decent short wave
could change that, but as noted by SPC in their day 4-5 outlook
early this morning, details and timing of such weak waves as
expected are too tricky to get excited about severe prospects. It
seems a wave coming across at the end of the week may be strong
enough to provide a dry weekend, but the above problem applies to
this idea also, and will keep the extended guidance mention of a
chance for Saturday.


&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1234 PM CDT Sat Jul 23 2016

VFR conditions rapidly returning as clearing arrives behind the
exiting band of thunderstorms. The main concern will be whether or
not convection can fire along a cold front now moving into central
SD. This front will quickly track east through the forecast area
this afternoon and evening. Models continue to suggest that the
convection will remain primarily north of the region, however
there will remain a 15 to 30 percent chance ahead of the front in
our forecast area late afternoon into late evening, with the best
chances in the highway 14 corridor/Buffalo Ridge area closest to
the main wave energy. Will leave out mention of tsra from TAF
sites, given that the best potential will be away from these
sites.


&&

.FSD Watches/Warnings/Advisories...
SD...Excessive Heat Warning until 7 PM CDT this evening for SDZ038-
     039-050-052>055-057>071.

MN...None.
IA...Excessive Heat Warning until 7 PM CDT this evening for IAZ001-
     012-020-031.

NE...Excessive Heat Warning until 7 PM CDT this evening for NEZ013-
     014.

&&

$$

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



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