416
FXUS63 KFSD 171837
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
137 PM CDT Mon Aug 17 2026

.KEY MESSAGES...

- Isolated to scattered storms remain possible late afternoon
  and evening, through development remains very uncertain. Risks
  of 1-2" hail and 60-70 mph will be possible.

- Greater storm potential arrives very late this evening and
  more likely overnight, with potential for a few bowing
  clusters of storms with gusty winds and marginal hail.

- Lingering rain early Tuesday will push the greatest risk of
  severe storms Tuesday further south. However cooler
  temperatures and clouds may linger deeper into the day.

- Rain chances persist Wednesday and Thursday, though storm
  track leads to lower confidence in where rain may fall.

&&

.DISCUSSION...
Issued at 132 PM CDT Mon Aug 17 2026

THIS AFTERNOON: Convection risks remain the primary focus in the
upcoming 24 hour period, as there continues to be uncertainty on if
we can advect sufficient moisture northward, and provide enough
focus of lift. Visible satellite this afternoon shows two areas
of interest, one area of ACCAS across northeastern South Dakota
and west central Minnesota, driven by 700 mb winds over the
crest of the Ridge. A second area of ACCAS drifting eastward out
of the Badlands area. At the surface, one concern has been a
slower arrival of boundary layer moisture as surface dewpoints
continue to linger in the upper 50s to lower 60s. Further south,
models continue to overestimate dew points in NE/KS, providing
some doubt on if the lower 70 dewpoints advertised by "high
instability" models can be realized.

The projections into the evening remain slightly uncertain with
several focusing mechanisms available.  A surface trough extending
from NW Minnesota into NE South Dakota and central South Dakota will
provide some minor convergence (focused greater over NW Minnesota
and eastern North Dakota).  A weaker pre-frontal trough in the NE
Panhandle into the Sandhills could also serve as a focal point.
Finally, a few storms may also develop over the Minnesota River
valley downstream of the Buffalo Ridge. Any storm that develops off
of these features will likely produced an increased risk for 1-2"
hail, but also 60-70 mph winds as MLCAPE pushes 2000+ J/KG and
effective shear climbs towards 40 knots.  Gradual east southeast
storm tracks within the mean flow are likely which could put
portions of SW Minnesota and the MO River valley into a higher early
evening risk. However the likely overestimation of surface dew
points, poor focus of convergence, and weak inhibition, may
also work to prohibit convection over a large part of the Tri-
State area into the evening.

Further west, additional isolated to scattered convection may form
over the western High Plains late this afternoon and evening
slightly stronger synoptic lift enters the area.  One or more
clusters of storms could reach the western CWA by mid-late evening,
bringing risks lower risk for hail, but higher risks for a few
stronger wind gusts. There continues to be some agreement in
mesoscale and lower resolution guidance that a subtle wave crossing
the Dakotas could keep scattered convection risks moving through the
CWA until at least 4am.  Weakening instability, and worsening lapse
rates should result in fewer strong to severe storms by daybreak
Tuesday. All this to say, coverage of this activity remains highly
in doubt, which will keep areal PoPs lower in general.

TUESDAY: Latest guidance continues to trend the greatest risks for
severe convection southward on Tuesday.  Overnight convection, along
with the passing shortwave should stabilize the area
considerably by daybreak, with a lingering marginal risks for
some crossover hail risks near 12Z. We may however see quite a
bit of stratus behind this wave, suggesting cooler than normal
temperatures into the afternoon.

WEDNESDAY-THURDAY: Upper troughing moving into Hudson Bay will
sharpen the NW flow over the Plains slightly by mid-week.
EC/GFS indicates vorticity crossing from the Pacific Northwest
through the Northern Rockies early on Wednesday pushing mid-lvl
lift towards the region early Wednesday. Differences on the
track of this wave keep PoPs lower, with GEFS/GFS further
northeast, and the EC leading to more impact through central
Nebraska instead. Another wave, along with a weak frontal
boundary approach Thursday afternoon. Depending on the amount of
inhibition nearby, a few thunderstorms could form along this
boundary late in the day.

FRIDAY-SUNDAY: Mid-lvl heights rise and the ridge sharpens over the
Rockies as we move into next weekend.  This transition of mid-lvl
flow could bring one final risk for elevated showers/TSRA early
Friday, but generally quiet and dry conditions then develop
into the weekend. Temperatures however will fall more under the
influence of Canadian high pressure in the Dakotas, suggesting
highs may stay in the upper 70s to lower 80s.

&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
Issued at 1212 PM CDT Mon Aug 17 2026

VFR conditions continue at mid-day, as a scattered mid-lvl cloud
field continues to drift east of I-29. We`ll continue to see a
slow influx of moisture northward this afternoon, and combined
with diurnal heating should result in scattered CU.

Convection chances really remain uncertain this afternoon and
evening. We are watching a subtle wave crossing the Black Hills
region which may reach the MO river valley by mid-afternoon.
This high based ACCAS could spark a few showers or even develop
further.

Any convection risks later this evening continue to appear
isolated in nature, with better focus into the overnight hours
as a wave approaches from the west. Given the uncertainty in
this wave/convection along with time in the TAF, will continue
to opt for Prob30 groups to show low probabilities.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Dux