265
FXUS63 KFSD 302253
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
553 PM CDT Sat Aug 30 2025

.KEY MESSAGES...

- An unsettled pattern will prevail through the holiday weekend,
  with highest rain chances toward the Missouri River Valley.
  The greater risk of heavy rainfall continue to sink southwards
  into northmen Nebraska.

- Drier conditions will be more dominant along and northeast of
  a line from Huron-Sioux Falls-Storm Lake, though scattered
  afternoon/evening showers are possible today through Monday.

- Severe weather risks are low, but non-zero risks for a few
  weak funnel clouds with developing "popcorn" showers during
  this afternoon-early evening hours as well as tomorrow
  afternoon-early evening as well.

- Chance of showers/storms lingers into Tuesday-Tuesday night.
  Some uncertainty in details, but the severe weather risk
  looks to remain low at this time.

- An impressive upper level low will bring a brief shot of
  colder air into parts of the Northern Plains/Upper Midwest
  Wednesday and Thursday next week.

&&

.DISCUSSION...
Issued at 257 PM CDT Sat Aug 30 2025

Mid-upper level low continues to wobble across northern Nebraska and
southern South Dakota this afternoon. Abundant cloud cover persists
across this area and bleeds over into the western half of the
forecast area. This has allowed for high temperatures to warm to the
mid to upper 70s along and east of a his line of showers looks to
develop along a Huron, South Dakota to Sioux Falls, South Dakota to
Storm Lake, Iowa line and only up to the upper 60s and low 70s west
of this line. Showers persist along and west of the James River this
afternoon. Good news is that the rain will remain light to only
moderate at times given the limited instability and lift in place.
That said, if these showers track or sit over any individual
location, then ponding on roadways and low lying areas would be
possible. At the same time, latest hi-res guidance continue to show
a small line of showers with some embedded lightning developing this
second half of the afternoon. This line of showers is starting to
develop along a the same line from Huron, South Dakota to Sioux
Falls, South Dakota to Storm Lake, Iowa line. This is also where an
axis of higher instability values on the order of 500-1000 J/kg of
CAPE is developing. No severe storms are expected thanks to weak
vertical shear profiles but with enhanced stretching values
increasing, still can`t rule out the low probability (<20% chance)
for a weak funnel cloud.

The showers look to persist through the overnight hours tonight in
the same general vicinity as the vertically stacked low wobbles its
way eastward. This will result in the showers expanding in coverage
across mainly the Missouri River valley. With abundant cloud cover
and showers around, low temperatures in the upper 50s and low 60s.

Sunday will be a rinse and repeat of Saturday with abundant cloud
cover and showers across the majority of the forecast area as the
previously mentioned upper low wobbles just a shade further north,
sending weak vorticity maxima`s into the area. This will result in
more widespread rain chances (40-80%) across the majority of the
area throughout the day, though the highest chances will remain
along the Missouri River. There could be some rumbles of thunder too
due to weak instability on the order of 500 J/kg or less. Given very
weak shear profiles and marginal instability, severe storms are not
expected. However, the enhanced stretching potential remains
heightened tomorrow afternoon while the non-supercell tornado
parameter also increases as well. Thus, think that the chance (20%
or less) for weak funnels will continue tomorrow as well. High
temperatures will remain in the 60s and 70s as well, coldest along
the Missouri River valley where the majority of rain is expected to
fall.

No break in the showers as the low continues to wobble across
northern Nebraska on Monday (Labor Day). This will keep persistent
chances (30-50%) for showers and isolated storms in the forecast
along with cooler highs remaining in the upper 60s and 70s. The good
news is that chances for rain will be on the downward trend Monday
evening as the low finally transitions to an open wave, increasing
its vorticity advection and thus pushing off to the south and east.
Low temperatures will fall a bit more, down to the 50s overnight.

There looks to be another shot of rain on Tuesday as a weak
shortwave trough passes down the more amplified northwest flow
aloft. Timing of this wave varies amongst medium range guidance.
But the ensembles are in fairly good agreement in their
probabilities for exceeding a tenth of an inch of rain. The
consensus is a broad 50-70% chance, likely due to a cold front that
will sweep through the Northern Plains during the overnight hours on
Tuesday. With this front passing through overnight, low temperatures
look to fall a bit more, down to the low to mid 50s. Do think that
the severe storm risk is low as of now as limited instability looks
to be in place and the cold front may outrun the better shear and QG
ascent behind it. Machine learning guidance is in agreement as only
one model shows a 5% chance for severe storms, with all other models
showing little to no support.

The upper wave tied to this cold front will be on the stronger side
as the ensembles show 500 mb heights on the order of 2 to 3 standard
deviations below average. In fact, the GFS and Euro ensembles show a
near 100% chance for 850 mb temperatures to fall below the 10th
percentile of climatology! This wave will result in a much cooler
Wednesday with high temperatures only warming to the upper 50s and
60s. With our more classic post cold frontal, northwest cold
advective flow regime in place, Wednesday will also be a breezy day
as well. Low temperatures look to fall to the 40s overnight but
could see lows potentially drop into the 30s as well.

This strong upper level low looks to spin over southern Canada for
the rest of the work week and into the weekend as well. With a much
drier airmass in place, no rain is expected. Thursday looks to be
the last day of below average temperatures with highs in the 60s
before highs moderate back to the 70s for Friday and Saturday.

&&

.AVIATION /00Z TAFS THROUGH 00Z MONDAY/...
Issued at 550 PM CDT Sat Aug 30 2025

Scattered showers and isolated thunderstorms will continue
across the area through the night, with the main focus being
through the MO river corridor with lesser chances to the north
and east. Showers and thunderstorms will slowly expand to the
north and east on Sunday, and along with that ceilings will lower
into the MVFR/IFR range. In addition, visibilities look to
lower into the MVFR/IFR range over the MO River corridor during
the day. Winds will continue to be light out of the
east/southeast through the period.

&&

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

&&

$$

DISCUSSION...Meyers
AVIATION...JM