236
FXUS63 KFSD 101703
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1203 PM CDT Mon Aug 10 2026

.KEY MESSAGES...

- Scattered thunderstorms will return late this evening in
  central SD. Storms may merge and move southeast overnight.
  Severe weather risks include 2 inch hail and 70 mph winds.

- Overnight storm chances will continue through at least
  Wednesday with the potential for stronger storms Tuesday and
  Wednesday night.

- Morning clouds and wildfire smoke aloft will continue to
  affect daytime heating leading to highs mainly in the 80s to
  low 90s through Wednesday. Cooler conditions will return by
  late week with highs in the 70s.

&&

.UPDATE...
Issued at 425 AM CDT Mon Aug 10 2026

Taking a look across the area, we`re continuing to see developing
showers weaken across central SD mostly due to the increasing
inhibition further eastwards. While this activity should continue to
feaster mainly north of I-90, any accumulations will be limited (If
any). From here, should see any lingering precipitation and stratus
gradually dissipate by mid-morning as diurnal resumes. Highs will
max out in the low to upper 80s with light southeasterly winds.
Otherwise, the forecast remains on track for additional showers and
thunderstorms this evening and overnight. Still looking like
clusters of showers and storms will likely develop across
western/central SD then follow the mean west-northwestly flow into
our area.

CAMs are still a bit split on if things can congeal into an
organized line or not. Based the orientation of the northern stream
jet, there could be either a broken line or multiple cluster
segments with this developing activity. With this in mind, large
hail up to 2-inches will be the main hazard with initial clusters.
When things grow upscale and become outflow dominant, damaging wind
gusts up to 65 mph will become the main concern. Lastly, timing is
still a bit uncertain due to differences in the progression and
evolution of this activity. As a result, a rough estimate of 9pm-6am
is about as close as we can get right now. As newer runs of guidance
come in, further refinement to the timing are this activity are
expected.

&&

.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 TUESDAY/...
Issued at 1159 AM CDT Mon Aug 10 2026

MVFR to low VFR stratus trying to develop early this afternoon.
These ceilings will rise slightly this afternoon but should
remain quite prominent into the evening.

A separate area of ACCAS will drift eastward toward the MO River
valley this afternoon, potentially producing a few sprinkles as
it moves through.

Greater risks for convection develop late this evening and
continue overnight as storms form over western and central South
Dakota. This activity may merge into one or more clusters and
impact the forecast area through 4am. Initially hail will be the
main risk, but storms may turn into linear lines of wind.
Confidence on impacts to the terminals remains low, so will
continue with a Prob30 to indicate potential. These risks may
increase quickly this evening.

Post convection, lower stratus may develop and continue into
mid-morning.

&&

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

&&

$$

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