948
FXUS63 KFSD 010213
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
913 PM CDT Mon Aug 31 2026

.KEY MESSAGES...

- More widespread thunderstorm chances return later Tuesday. A
  few strong to severe storms are possible between 6 pm Tuesday
  and 2 am Wednesday. Golf ball sized hail and damaging winds to
  70 mph are the main threats, although a tornado cannot be
  ruled out.

- Near to above normal temperatures continue this week.
  Confidence is increasing in higher temperatures and humidity
  for the end of this week and weekend.

- Low chances (15-30%) for rain accompanies increasing heat and
  humidity by the end of week.


&&

.UPDATE...
Issued at 912 PM CDT Mon Aug 31 2026

Mild but pleasant evening with temperatures in the 60s and 70s,
falling into the 60s tonight winds with light winds and mostly clear
skies.

Into tonight, will be keeping an eye on showers/storms developing
over central NE with the LLJ, a 700mb wave, and some WAA. Not
expecting any strong to severe storms with limited moisture and
instability and activity likely elevated despite the surface front
moving north. No major changes to the forecast this evening, but
made some minor changes to pops. Think that overnight and pre-
daybreak showers/storms will be limited in scope to the US Hwy 20
corridor/northwestern IA and maybe into the southern MO River
Valley, but CAMs remain quite varied on the coverage and timing of
this activity.

Inverted surface front hangs around during the day and into the
evening tomorrow, with better dynamic forcing coming in from the
west with and ahead of the next wave. Guidance this afternoon and
this evening seems more convoluted than this time yesterday, making
confidence in guidance (especially CAMs) a bit lower. Biggest
questions for Tuesday remain how late morning convection lingers,
possibly keeping things a bit more stable into the afternoon and
evening - or at least limiting recovery time. Could see some
additional isolated activity along the stalled front into the early
afternoon, but the main focus will be on the main wave moving in
from the west late afternoon through Tuesday night. No significant
changes to severe potential or timing.

&&

.DISCUSSION...
Issued at 245 PM CDT Mon Aug 31 2026

Sunny and warm conditions persist this afternoon as temperatures
have warmed to 80s. With a cold front now southeast of the area, dew
points have lowered to 50s and 60s. Still seeing heat indices up to
80s to low 90s, so some humid conditions remain though not as humid
as what we saw this weekend. A weak low level jet (LLJ) is expected
to develop tonight which will develop showers and potentially an
isolated thunderstorm across Nebraska. These showers will push
east/northeastwards into a worsening environment. They could still
be capable of lightning though not expected to be strong nor severe.
Low temperatures will remain quite mild overnight, with lows only
falling to the 60s.

The showers will push through the area during the morning to early
afternoon hours. This will leave the rest of the afternoon on the
dry side of things. With some cloud cover remaining aloft, highs
look to remain warm but be slightly cooler than Monday`s highs with
temperatures in the 80s up to about 90F. Chances for severe storms
begin to increase after 6 pm as a shortwave trough ejects out of the
Rockies and into the Northern Plains. The previously mentioned front
will begin to return northwards as a warm front due to the mass
response from the wave. A sufficient warm sector will be in place
ahead of the boundary with dew points in the 60s to 70s. Some
capping will be in place which may limit the extent of convection
early on. Latest hi-res guidance continues to show moderate variance
but is beginning to show a consensus of storms developing across
central and north central Nebraska and possibly south central South
Dakota. These showers and storms will push into the area during the
evening timeframe but the remaining uncertainty revolves around
storm mode. Think a custer of storms is possible with embedded multi-
cells to even supercells. As the storms push further into the
forecast area, they will become more elevated due to increased
capping over the area. Storm mode becomes more questionable here as
storms may remain a bit more discrete to perhaps remaining in a
cluster. Or if they can congeal cold pools properly, upscale growth
into a line is possible. Tough to say which storm mode is correct at
this time. Aside from capping, sufficient elevated instability will
be in place with CAPE values up to 1,000 J/kg to 2,000 J/kg with
effective shear values between 40-50 knots. Thus, damaging winds to
70 mph and golf ball size hail will be the main hazards. If a storm
is able to tap into the boundary layer, then an isolated tornado
will be possible. Especially if the surface warm front can push into
the forecast area. The storms will push through the area through the
evening and at least the first half of the overnight hours before
pushing eastwards with the veering low level jet.

The daylight hours on Wednesday look to be a quiet as subsidence
prevails on the backside of the departing wave. Highs will remain
consistent in the 80s to even low 90s in a few locations. The break
from rain will be short lived though as another shortwave trough
will be pushing into the Plains Wednesday night. The ensembles
support this as they show increasing probabilities up to a 20-50%
chance for rainfall totals to exceed a tenth of an inch. The
ensembles have the highest chances for rain east of I-29. Some
elevated instability looks to be available, suggesting that
thunderstorms will again be possible. Whether they will be strong to
severe is uncertain at this time.

Upper level ridging will be strengthening aloft for the end of this
week and weekend. High temperatures look to not only remain above
average but further warm as the ridge becomes more pronounced aloft.
The ensembles not only support this ridge developing, but also 850
mb temperatures being pushed to the the 99th percentile of
climatology. The Euro Extreme Forecast Index (EFI) further supports
this as it shows 60-80% of its members suggesting above average
temperatures are possible. Humid conditions look to accompany the
above average temperatures as the ensembles show a broad 50-90%
chance for heat indices to exceed 90F. Chances for rain are possible
(15-30% chance) during this period of time but details are highly
uncertain. There are some signals that this pattern could begin to
break down next week. However, medium range guidance continues to
show increasing variance in this potential. Something to watch to
see if these conditions will persist into next week.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 656 PM CDT Mon Aug 31 2026

VFR conditions expected through tonight. Shower and storm
chances will begin to increase around the Missouri River Valley by
daybreak Tuesday and gradually lift northward through the afternoon.
Overall, low confidence in the coverage of showers and storms, but
enough to include a PROB30 group for -TSRA at KSUX. As showers and
storms lift north, overall coverage may decrease a bit so left KHON
and KFSD dry at this time.

Winds will be mainly light and variable through mid morning, only
ticking up slightly during the afternoon around 5-8 kts.

&&

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

&&

$$

UPDATE...SG
DISCUSSION...Meyers
AVIATION...Samet