822
FXUS63 KFSD 290144 CCA
AFDFSD

Area Forecast Discussion...CORRECTION
National Weather Service Sioux Falls SD
843 PM CDT Fri Aug 28 2026

.KEY MESSAGES...

- 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.

- A Marginal Risk (level 1 of 5) for severe thunderstorms
  remains in place into early Saturday morning. Widespread
  severe weather is not expected, but isolated stronger storms
  may produce up to ping pong ball sized hail and 60 mph wind
  gusts.

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

&&

.UPDATE...
Issued at 837 PM CDT Fri Aug 28 2026

High based showers/sprinkles and very isolated lightning strikes
continue to move east this evening along the initial wave and WAA
around 850 mb. Further west closer to the main wave toward the Black
Hills, convection has continued to struggle as any development
quickly weakens. Will see if this trend holds. CAMs continue to
develop convection to our west with every run this evening along the
edge of convergence, and that convection has yet to develop and move
east thus far. That said, still anticipate some increase in elevated
showers and isolated storms as the LLJ strengthens and the better
wave moves east. Confidence in any potential severe weather is low;
soundings are not supportive of much severe weather with a lack of
appreciable moisture and strong cap keeping storms elevated. If a
stronger storm could rotate and tap into the modest shear, ping pong
ball sized hail would be possible. Can`t entirely rule out a 60 mph
wind gust either, although this might be harder to come by with the
aforementioned cap. Showers and storms push east through the early
morning hours of Saturday.

Changes to the forecast this evening have been focused on refining
pops over the next 12 hours. No other significant changes, with
other elements still generally on track. Still looks like a hot and
humid day for most Saturday.

&&

.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 /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 617 PM CDT Fri Aug 28 2026

High based showers and very isolated storms continue moving
east across the area this evening. Have narrowed timing of TSRA
for KHON for the next few hours, as we may struggle for TS later
in the evening. For the rest of tonight, additional showers and
storms are expected to develop with the LLJ. Again, narrowed
timing for KFSD and limited mention a bit more at KSUX, which
may now be on the far southern end of any development.
Showers/storms should move east of the area by mid morning
Saturday.

Directional LLWS may develop overnight south of I-90 with the
LLJ. Maintained mention at KSUX, and think that speed shear will
be more marginal to below criteria with continued gusts around
20-25 knots overnight. Winds remain either side of south
through into Saturday morning and afternoon, before becoming
light and somewhat variable from west to east at the end of the
period.

Largely VFR conditions prevail, outside of some very splotchy
MVFR conditions if we get some heavier rain.

&&

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

&&

$$

UPDATE...SG
DISCUSSION...AJP
AVIATION...SG