091
FXUS63 KFSD 291138
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
638 AM CDT Sat Aug 29 2026

.KEY MESSAGES...

- Scattered showers and thunderstorms will continue to progress
  through the area through daybreak. The severe weather risk is
  low but not zero.

- Warm and humid conditions continue into the weekend. Afternoon
  heat indices may approach 100F in portions of the Missouri
  River Valley Saturday/Sunday as temperatures climb into the
  90s.

- Periodic shower and storm chances continue this weekend into
  early next week. Confidence on any details is low.

&&

.UPDATE...
Issued at 256 AM CDT Sat Aug 29 2026

Taking a look across the area, we`re continues to monitor lingering
showers and storms north of I-90 this morning. While most of this
activity is being spurred by the nocturnal LLJ, current thinking is
this activity should continue to progress to the east-southeast
following the mid-level shortwave through about daybreak (5am-7am)
before exiting our area. While the risk severe storms is low, strong
gusts between 40-50 mph and small hail up to dime size will be
possible over the next few hours. Otherwise, the forecast remains on
track as combination of southwesterly surface winds and lingering
warm air advection (WAA) helps highs approach the mid 80s to mid 90s
for the day.

With dew points in the upper 60s to low 70s expected to accompany
this heat this afternoon, heat index values will creep up
towards the upper 90s to low 100s with the warmest conditions
along the Missouri River Valley. With this in mind, make sure to
stay hydrated especially if you have any outdoor/tailgating
plans this afternoon. Lastly, an active pattern aloft with usher
in another shortwave from the Black Hills to northeastern SD
tonight. While the strongest dynamics will likely be focused to
the north and northwest of us, can`t rule out pockets of
isolated to scattered showers through Sunday morning with very
low chances for stronger storms.

&&

.DISCUSSION...
Issued at 316 PM CDT Fri Aug 28 2026

Today will be partly cloudy and breezy. Southerly winds increase
through the morning as an upper shortwave and surface low pressure
move in from the west. Areas along and west of I-29 can expect gusts
of 20-30 mph with the strongest gusts over south central South
Dakota. Here occasional gusts to 35 mph are possible. Areas to
the east of I-29 will see gusts of 20 mph or less. Winds will
bring in warmer temperatures and moisture, boosting dew points
into the mid to upper 60s F. With highs expected to climb into
the 80s and low 90s today will feel bit muggy.

This afternoon and through the overnight SPC has issued a Day 1
Marginal (level 1 of 5) Risk for severe thunderstorms that covers
most of the CWA. A marginal to slightly unstable environment will
develop through today with 1500-2500 J/kg of MUCAPE, 35-45 kts of
deep layer shear, and steep mid-level lapse rates. However,
uncertainty in storm development is high due to a couple of factors.
First is cloud cover, should morning clouds linger through the day
it may limit surface heating, therefore limiting instability.
Guidance has some variation on the timing of the wave and
amplification of the LLJ. The GFS and EC continue to have the wave
and LLJ move through earlier, while the CAN and NAM are slower.
Similarly, CAMs guidance is split with the HRRR, NamNest, and RAP13
showing earlier initiation while the ARW and FV3 are later. With the
earlier solutions it is more likely that initial convection will
begin as super cells that grow upscale into a line, possibly with
bowing segments. The slower solutions will more likely begin as
elevated multicell convection that grows into a line with bowing
segments. As of 2:30 pm CDT a cumulus field is forming over western
and central South Dakota, some producing light radar echoes. This
could be an indication that the cap is weakening, thus an indication
that earlier convective initiation may be the correct solution. That
being said, the greatest severe risk still looks to be between 10 pm
tonight through 6 am Saturday. Hazards are heavy rain, 1.5 to 2 inch
hail (with supercells west of the James River Valley), and wind
gusts 60-65 mph. As storm progress east they will become elevated
and transition to more of a wind and heavy rain threat. Greatest
risk area is along and north of I-90.

A few showers and storms may linger into mid-Saturday morning before
pushing east of the CWA. Through the day the surface low associated
with the previous storms will drift east, pushing clouds out of the
region. Southerly winds will remain breezy gusting up to 30 mph.
Warm and moist air continues to advect into the region. Highs will
climb into the upper 80s to mid 90s, and dew points to the mid 60s
to low 70s. Heat Index values will climb into the 90s, with areas
along the southern Missouri River Valley potentially reaching 100.
At this time a Heat Advisory is not necessary, however we will
monitor the trends. Storm chances return for late Saturday evening
into Sunday morning. Looking aloft a deepening upper trough will
push east into the north central Rockies. On the east side of the
mountains a subtle mid-level lee trough and surface low form. As
this begins to drift east late in the afternoon along with an area
of enhanced vorticity it could trigger showers and thunderstorms. A
marginally unstable environment with steep mid-level lapse rates and
35 kts of deep layer shear may support isolated to scattered strong
to severe thunderstorms, mainly over central South Dakota. SPC has
issued a Day 2 Marginal Risk west of a line from roughly Huron, to
Plankinton, to Bonesteel. For this area hazards include large
hail and damaging wind gusts. As storms drift east they will
encounter a less favorable environment and should weaken.
Similar to Friday- Saturday, confidence in storm formation is
low due to the conditional nature of cloud clearing, a strongly
capped environment, and variance in guidance on storm track and
timing.

Sunday brings yet a third round of potentially strong to severe
thunderstorms. SPC has issued a Day 3 Marginal that encompasses
the entire CWA. A marginally unstable environment is expected
for the afternoon and evening. Stronger forcing this round as an
upper closed low skirting the international border drags a cold
front through the northern Plains Sunday evening into Monday
morning. Mid- range guidance is in very low agreement on track
and timing of this system. In addition, south to southwest winds
for western and central South Dakota advect in a drier air mass
than the previous two days. This general lack of moisture will
likely prevent convection from forming over this region. At the
same time over eastern South Dakota and Nebraska, and western
Minnesota and Iowa moisture rich air will pool south of the warm
front. As the cold front approaches this area showers and
thunderstorms may form. Coverage of storms will depend on how
far west the moisture rich air flows

A weak upper ridge builds in through the day Monday. A series of
"ridge rider" short waves keep storm chances in the forecast nearly
daily for much of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SUNDAY/...
Issued at 635 AM CDT Sat Aug 29 2026

Mainly VFR conditions will continue this TAF period. Taking a
look at satellite imagery, we`re continuing to watch showers and
thunderstorms progress through portions of northwestern IA this
morning. Should see conditions gradually clear by mid-morning
giving way to more VFR conditions. Otherwise, southeasterly
winds will become more southwesterly winds by this afternoon
with gusts between 20-30 mph possible at times.

&&

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

&&

$$

UPDATE...05
DISCUSSION...AJP
AVIATION...05