402
FXUS63 KFSD 111140
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
640 AM CDT Tue Aug 11 2026

.KEY MESSAGES...

- Any lingering showers or storms should dissipate by daybreak
  this morning.

- Another round of strong to severe storms could develop late
  this evening into the overnight hours. These storms could also
  form into another storm cluster that moves southeast into
  Wednesday.

- Expect a cooler, unsettled pattern from Thursday through the
  weekend with high temperatures dropping into the mid-70s.
  Daily rain chances return, but the severe weather risks are
  expected to remain low.

&&

.UPDATE...
Issued at 435 AM CDT Tue Aug 11 2026

Taking a look across the area, the main focus continues to be south
of I-90 where clusters of showers and thunderstorms continue their
gradual track eastwards. Besides pockets of moderate to heavy
rainfall, marginally large hail up to the size of quarters has been
the main concern so far. While the low-end severe risk could
continue over the next few hours, expect most of this activity to
push eastwards out of our area between 5 am to 6 am. From here, the
good news is quieter conditions will likely return for the daylight
hours as highs peak in the low to upper 80s across the area. However,
this will be short-lived as the "wave train" continues aloft.
Similar to last night, another wave will ride the west-northwest
flow into our area overnight potentially triggering scattered
showers and thunderstorms mainly across southcentral SD.

With a slightly weakening cap according to soundings, there could be
a conditional chance for a few stronger storms if parcels can become
more elevated. IF that occurs, developing storms would have access
to a decently unstable environment characterized by 1500-2000 J/kg
of CAPE and 30-40 kts of shear. Storms would then quickly become
severe with the main hazards being golf ball-sized hail and damaging
winds up to 60 mph. However, if the cap is stronger than expected;
there is a real chance that we don`t get anything besides a few
elevated showers. Since the CAMs still don`t have a clue on how
things are evolving on radar currently, not expecting a much better
for tonight. With all this in mind, still too early to decide which
scenario will prevail so we`ll just have to wait and see.

&&

.DISCUSSION...
Issued at 110 PM CDT Mon Aug 10 2026

THIS AFTERNOON: Quite a bit of strato-cu out there this afternoon,
delineating the area where more abundant low-lvl moisture has
pooled.  Further west an area of ACCAS tied to modest mid-lvl theta-
e advection continues to drift eastward.  We`ll have to watch this
area, but would not anticipate any more than sprinkles as it slides
east later today. A light southeasterly wind is expected to continue
a push of upper 60 to lower 70 dewpoints northwest into portions of
northwestern SD, where a focused risk for severe storms will develop
later this evening.  With the increased cloud cover and abundant
wildfire smoke aloft, high temperatures may struggle to reach
much past the middle 80s.

TONIGHT:  Convection risks remain the highest concern into the
evening and overnight hours.  Water vapor imagery this morning
showed a subtle shortwave trough moving through eastern MT, with
this waved modeled to dip southeast this evening. A deep instability
pool has pushed into western SD this afternoon, with upwards of 3000
J/KG MLCAPE.  The issue may be some inhibition, impact of wildfire
smoke, and lack of a focused trigger which could delay widespread
development. CAMS however continue to hint at deeper convection
waiting a few hours into the evening, and then triggering due to an
increase of 850:700 mb warm advection in the West River areas as
stronger vorticity moves into the Dakotas. This northward LLJ should
also help push deeper instability further northeast over the eastern
portions of SD. Where storms develop, signals will be strong for at
least 2" hail, as elevated parcels will be within a corridor of 50
knots effective shear and should rotate. An increase of mid-lvl dry
air will increase the potential for cold pool development in
supercells, eventually suggesting one or more larger clusters of
storms will form and try to track southeast after 10pm. Initial
SCCRAM+HRRR guidance suggest rapidly increasing severe weather
probabilities as early as 0-2 UTC in central South Dakota.
After this, HREF 2-5 km UH paintball plots all indicate a
tendency for this activity to track southeast along the
instability axis reaching I- 29 around 12-1am and reaching the
edge of the CWA around 4am. As stated earlier, initial updrafts
may have potential for 2" hail, with greater risks for 50 to 70
mph winds in progressive clusters. This entire setup remains a
bit uncertain, so it`s imperative to continue monitoring the
forecast.

TUESDAY-TUESDAY NIGHT:  Behind any departing MCS we`ll have a fair
degree of stability and subsidence that could leave stratus in place
in the morning. Warming in the afternoon and another potential
shortwave crossing the Rockies could promote strong to severe storms
over western and central SD/ND by the evening with another MCS or
two moving southeast overnight.  Guidance remains all over the place
as it continues to struggle with resolving these embedded
waves. Nevertheless, SPC slight risks could end up extending
further southeast in subsequent updates.

WEDNESDAY-SUNDAY: Feel that most of Wednesday will again remain dry
as shortwave ridging moves in and surface winds remain easterly.
High temperatures will rise into the lower to mid 80s. The ridge
centered over the Four Corners and responsible for multiple days of
NW flow will shift eastward by the second half of the work week.
This pattern shift will cause the ridge to flatten slightly in the
Northern Plains, inducing slight westerly to southwesterly flow
aloft into the weekend.  We`ll be subject to smaller embedded lobes
of vorticity tracking northeast from the southwestern CONUS and
Central Rockies.  Medium range guidance is not handling this
transition well, but seems to continue to bring nearly daily chances
for rain into the weekend.  At this point I highly doubt every day
will feature rain, but there will be some increased potential for
more showery activity at times Thursday and again late Friday into
Saturday.  Instability looks low, so severe weather risks should
also remain low. Temperatures with more cloud cover and cooler
influences of Canadian high pressure should trend into the middle
70s into the weekend.

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 630 AM CDT Tue Aug 11 2026

Taking a look at satellite imagery, we continue to see stratus
and fog developing in the wake of this morning`s precipitation
leading to mainly MVFR to LIFR conditions this morning. While
these conditions could persist through the late morning, still
thinking diurnal heating will gradually bring things back to VFR
conditions by early afternoon. Otherwise, lighter surface winds
will continue for most of the day. Lastly, while additional
showers and thunderstorms will be possible; current trends have
things sticking to the southcentral SD so kept any mentionable
precipitation out of our TAF sites for now.

&&

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

&&

$$

UPDATE...05
DISCUSSION...Dux
AVIATION...05