039
FXUS63 KFSD 311144
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
644 AM CDT Sun Aug 31 2025

.KEY MESSAGES...

- An unsettled pattern persists through Labor Day. The highest
  overall rain chances remain south of I-90, however scattered
  afternoon/evening showers and storms will occur farther to the
  north.

- Widespread heavy rain is not expected, but ribbons of heavier
  rainfall exceeding an inch are possible where narrow bands of
  showers/storms persist for multiple hours.

- Severe weather risk is low, but we continue to see a non-zero
  risk for weak funnel clouds with developing air mass showers
  during the afternoon-early evening.

- Chance of showers/storms lingers into Tuesday-Tuesday night.
  The severe weather risk remains low.

- An unseasonably strong upper level low will bring a shot of
  colder air to parts of the Northern Plains/Upper Midwest mid
  to late week.

&&

.DISCUSSION...
Issued at 415 AM CDT Sun Aug 31 2025

SUNDAY-LABOR DAY: A slow moving mid-upper level low over eastern
Nebraska will continue to drift southeast over the next 24-48
hours. This feature will keep a moderate to high (50-80%) chance
of showers and a few thunderstorms across our southern forecast
area into Monday, though chances will gradually wane from north
to south Monday into Monday night as the low slides farther away
from our area.

Areas roughly north of I-90, perhaps more along a line from
Huron-Sioux Falls-Spencer Iowa, the nighttime-morning hours will
tend to be on the drier side. However, similar to Saturday,
diurnal heating will support bands of showers and scattered
storms rotating west-northwest around the upper low to our
south. This will result in highly variable rainfall across the
area, but as we saw yesterday, if these showers/storms track
along the same trajectory with little north-south variation in
the band location, narrow ribbons of heavier rainfall will again
be possible. Very difficult to project exactly where these narrow
ribbons will occur, though, and as such the QPF forecast is low
confidence.

By Monday afternoon/evening, as the low is farther southeast,
we should begin to see some influence of drier air with a lesser
chance of locally heavy rainfall.

High temperatures for the latter half of the holiday weekend
should again be highly dependent on rain coverage. Cooler temps
holding in the mid-upper 60s are more likely in our southwest
and south where rain could be more prevalent, while northeast
areas where we could see some sunshine should reach at least
lower-mid 70s.

TUESDAY-EARLY WEDNESDAY: A much stronger northern stream trough
will drop south into the northern Plains-Upper Midwest Tuesday
night into Wednesday. While the main cold front will accompany
the trough during this period, a pre-frontal trough and leading
weak wave will keep a chance for scattered showers/storms over
the area Tuesday-Tuesday night. Although deep layer shear does
increase slightly with 30+kt possible Tuesday afternoon-evening,
mid-level lapse rates remain unimpressive and DCAPE is also weak
within the area of expected showers. Thus the severe weather
risk continues to look low for this period.

LATER WEDNESDAY-SATURDAY: Latest deterministic models keep the
brunt of the cold air with a strong secondary cold front over
Minnesota, grazing just the northeast portion of our forecast
area Wednesday night-early Thursday before slightly warmer air
builds back in from the west. That said, the latter half of the
week continues to look below normal for temperatures, but some
uncertainty in just how far below our early September normal
highs around 80F. Given the proximity of the stout upper low,
cannot rule out spotty diurnal shower activity, but confidence
in location is low, so will stick with a dry late week forecast
for now.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 644 AM CDT Sun Aug 31 2025

We start the day with areas of dense fog in southwest Minnesota
with scattered light showers and areas of MVFR to IFR ceilings
across the western and southern portions of the forecast area.

Similar to Saturday, expect fog and ceilings to lift to VFR
levels in most areas by midday, with a broader coverage of
scattered showers and thunderstorms during the afternoon to
evening hours. While there is some uncertainty whether TAF sites
will be directly impacted by the late day storms, did include a
mention at both KHON/KFSD for a few hours.

Potential for thunder wanes after 01Z-02Z, but spotty showers
may linger, with lower stratus and fog again possible by the end
of this TAF period.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ071-072-
     080-081-089-090.
IA...None.
NE...None.

&&

$$

DISCUSSION...JH
AVIATION...JH