752
FXUS63 KFSD 110230
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
930 PM CDT Mon Aug 10 2026

.KEY MESSAGES...

- Strong to severe thunderstorms are the primary concern
  tonight. Initial storms west of our forecast area pose a risk
  for hail up to 2", evolving into linear clusters through the
  early morning hours.

- Another round of strong to severe storms could develop late
  Tuesday afternoon and evening. 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 930 PM CDT Mon Aug 10 2026

Initial development over the western Dakotas has been slow and
quite isolated, with main focus on a small cluster of storms
which has moved from far southwest North Dakota into northwest
South Dakota north of Faith. 00Z data continues to trickle in,
and consensus continues to show this small cluster growing
upscale into bowing segments which track southeast across our
forecast area overnight through Tuesday morning, though the HRRR
remains much less aggressive than other CAMs in how quickly, or
even if the storms evolve into a large bowing line, so still
some uncertainty in the coverage of severe potential.

The primary change is a significant slow-down in timing by as
much as 2-3 hours over previous thinking. Likely will be playing
a waiting game in our CWA until close to midnight to 1 AM, with
storms then persisting until sunrise or shortly thereafter.

With the slower and more westward development, thinking the hail
threat is decreasing for even our far western counties, though
cannot rule out an isolated core dropping quarters to perhaps up
to ping pong ball size. The greater threat is by far potential
damaging wind, but just how widespread vs localized is still to
be determined.

&&

.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 /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 659 PM CDT Mon Aug 10 2026

Thunderstorm chances, including a potential for strong to
damaging wind, will be the main concern through this TAF period.
While there is still uncertainty regarding the exact track and
timing of storms, seeing modest consensus in the latest data
that suggests storms currently developing in the far western
Dakotas may evolve into a cluster that will impact one or more
of our TAF locations overnight into early Tuesday morning
(05Z-11Z window). With a slight uptick in confidence, have
bumped PROB30 groups to TEMPO and also introduced the potential
for stronger winds with the storms for KFSD/KSUX.

Storms may be followed by a period of MVFR ceilings which should
erode to VFR by mid-morning Tuesday.

&&

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

&&

$$

UPDATE...JH
DISCUSSION...Dux
AVIATION...JH