196
FXUS63 KFSD 091832
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
132 PM CDT Sun Aug 9 2026

.KEY MESSAGES...

- Expect reoccurring morning fog and potentially low stratus
  through the area until at least Tuesday morning.

- Isolated overnight storm clusters are possible each night
  through early Wednesday. Risks tonight in any storm that
  develops will be golf ball size hail, mostly west of the
  James River.

- Highs will remain in the 80s through Wednesday, with daytime
  heating impacted by morning clouds and high level smoke. Highs
  in the 70s are possible by the end of the week/weekend.

- Forecast confidence drops from Thursday to Saturday, with a
  daily 20 to 30% rain chance, meaning rain is far from
  guaranteed.

&&

.DISCUSSION...
Issued at 122 PM CDT Sun Aug 9 2026

THIS AFTERNOON: Cool northeasterly surface and low level flow has
brought widespread stratus into the region this afternoon. We`re
gradually seeing this cloud layer mix-out, which should still result
in a brief window of highs in the lower 80s.  Further west, lots of
mid-high level AC moving eastward towards the central Dakotas. These
clouds, tied to weak dPVA at the 600:500 mb layer, will continue to
push eastward this evening.  Below this cloud layer, soundings
indicate a very stout and deep dry layer which should prevent
anything more than a few sprinkles reaching the ground later this
afternoon/evening.

TONIGHT:  A very tricky and uncertain forecast continues into
Monday, as no clear forcing mechanisms to develop convection are
present at this point. Despite the pesky northwest flow pattern,
most CAMs and global models have backed off on surface based
convection over the western Dakotas this afternoon and evening. The
thick layer of smoke aloft could potentially cause some limitation
on convective development, but also the lack of any clear defined
shortwave in the flow.  Now with that said, there are a few hints at
some weak 700 mb warm advection trying to develop after midnight
(perhaps closer to 3-4am) into central South Dakota.  A parcel
lifted off the 700 mb layer should have upwards of 2000 J/KG MUCAPE
with upwards of 25 knots of shear.  Thus if a storm develops, it
could briefly produce golf ball size hail and some modest wind
gusts. The eastward movement of this activity beyond the James
River should be limited by lingering low-lvl dry air. Elsewhere,
given low-lvl subsidence continuing into the overnight hours,
along with boundary layer dew points in the 70s, there will also
be concern for fog/stratus development.

MONDAY: Any morning convection should again weaken by mid-morning,
leaving potential stratus and fog in place through the morning in a
light east southeast wind. Eventually temperatures do rise into the
low to middle 80s, but smoke aloft could again limit the rise of
temperatures.  There still appears to be a better signal for a
passing shortwave Monday night into Tuesday capable of producing
evening convection over the western Dakotas/Nebraska.   The residual
moderate elevated instability, and steepening mid-lvl lapse rates,
combining with an increasing nocturnal LLJ should be able to produce
one or more clusters of stronger storms moving eastward towards
central SD into the overnight hours. However soundings present more
and more inhibition as storms move into the CWA.

TUESDAY: A bit of a rinse and repeat forecast for Tuesday as we may
again start the day with stratus and some fog and even a few
lingering elevated thunderstorms. Gradual upslope flow on the
Plains Tuesday afternoon/evening may again develop one or more
clusters of convection that may move towards the CWA into
Wednesday morning.

WEDNESDAY: Wednesday continues to look like a quiet day in the
region with more influence from minor ridging in the Plains.
Temperatures with a light wind will rise towards the lower to
middle 80s. By the overnight hours, some potential for MCS
activity in KS/NE will attempt to move eastward and could bring
some thunderstorm risks to the MO river valley.

THURSDAY-SATURDAY: Confidence remains rather low in the extended as
the mid-lvl pattern shifts from a quasi-northwest flow to zonal by
the end of the week. Several waves are likely to traverse these
westerlies in the weekend, but a wide array of solutions continues
to keep lower PoPs (20-30%) for multiple days. In reality, chances
are likely going to be more limited than the NBM would suggest,
however model spread will need to tighten before a better timing
could be had.  Confidence is a bit higher on the slight cooldown of
temperatures into the 70s into next week.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1204 PM CDT Sun Aug 9 2026

MVFR ceilings will persist into the early and middle afternoon
hours. We`ll continue to see light winds, with ceilings
gradually mixing upwards to VFR levels by mid-afternoon. Further
west, very high based AC field AOA 15K ft AGL will move
eastward. There could be enough lift in this layer for a few
sprinkles, but a really dry airmass continues between this layer
and the low strato-cu layer suggesting nothing will reach the
ground.

Into the overnight hours, the only really strong potential for
convection will be in western SD and perhaps central SD after
midnight. Though significant uncertainty remains on if storms
will actually develop. Further east, residual moisture could
lead to some low stratus or fog development.

&&

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

&&

$$

DISCUSSION...Dux
AVIATION...Dux