277
FXUS63 KFSD 270824
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
324 AM CDT Sun Sep 27 2026

.KEY MESSAGES...

- Dense fog becoming more widespread near and west of the James
  River Valley early this morning, with patchy dense fog in the
  higher elevations farther east across the Coteau des Prairies
  and Buffalo Ridge.

- Spotty showers/drizzle continue early this morning near and
  east of I-29. Coverage should continue to decrease, but low
  level moisture may continue to produce isolated sprinkles or
  drizzle through tonight.

- Greater chances for showers and a few thunderstorms Monday
  night into Tuesday. Pockets of heavier rainfall will again be
  the primary concern.

&&

.UPDATE...
Issued at 320 AM CDT Sun Sep 27 2026

Stratus has gradually thinned/cleared across western portions of
the forecast area overnight, but any clearing quickly allows fog
to develop in its place. Already issued a Dense Fog Advisory for
much of the western CWA and will continue to monitor for possible
expansion through the pre-dawn hours.

Meanwhile, eastern portions of the area currently remain under a
thicker stratus deck, though patches of clearing have been noted
in portions of far southeast SD. Still seeing signs of light rain
or drizzle in portions of southwest Minnesota/northwest Iowa, so
have increased pops a bit for the next 2-3 hours as the subtle
wave slowly exits the area. Cannot rule out lingering very light
drizzle beneath any thicker stratus this morning, with a shallow
convective layer beneath a strong inversion and additional mid
level instability potentially producing spotty sprinkles/light
showers across the area this afternoon into the early evening.

Unfortunately, some forecast soundings indicate another round of
thicker stratus developing late tonight into Monday morning with
a potential for another drizzly start to the work week. This does
not seem an unreasonable solution as a persistent southeast flow
does not bring a strong dry push into the area. Confidence is not
high enough to introduce the drizzle into Monday morning just yet,
but will be something to consider in later forecasts.

&&

.DISCUSSION...
Issued at 257 PM CDT Sat Sep 26 2026

The area of steady moderate rain that impacted the area
this morning is exiting off to our northeast; however, patchy
drizzle continues and will continue on and off through the afternoon
where clouds ceilings are lowest, which is generally from far
eastern South Dakota into southwest Minnesota. Farther west, we`ve
seen some breaks in the lowest clouds, allowing for some
destabilization to occur. Up to 500-1,000 J/kg of MLCAPE has
developed per latest SPC Mesoanalysis along the Missouri River
Valley, and as a secondary mid level wave moves across the area, a
few weak thunderstorms have already developed over northern Nebraska
and are lifting northward. Severe weather is not expected given weak
shear across the area, but we will likely continue to see some
additional showers and isolated thunderstorms develop through the
afternoon and evening. The best chance of rain (30-60%) with this
activity will be over western Iowa, far northeast Nebraska, and far
southeast South Dakota, stretching to far southern Minnesota by the
late night hours. Tall, skinny CAPE profiles and deep warm cloud
layers suggest heavy rain will be the primary threat with any
thunderstorm. This could lead to a few pockets of ponding in low-
lying and poor drainage areas, but flash flooding is unlikely.

Heading into tonight, the areas that saw some clearing stratus
(primarily near and west of the James River) will see some fog
develop, meanwhile the stratus deck elsewhere is expected to lower
through the night and become fog. Locally dense fog is likely given
all the near surface moisture, though coverage and exact locations
where the densest fog will reside precludes a need for a Dense Fog
Advisory at this time, but trends will be monitored. This fog will
gradually lift through the mid morning hours, but likely become low
stratus heading into much of the day on Sunday. Still the potential
for some of this stratus to mix out a bit and allow for brief breaks
of sun mainly near and west of the James River, but this will likely
be the exception, not the norm across the area. Some instability in
the low cloud layer may allow for a few sprinkles to spits of
drizzle, but it`s not looking as persistent as it has been the past
couple of days.

Heading into early next week, a trough over the West Coast will
begin to dig into the Desert Southwest. Ahead of this, an upper
wave will move into the area late Monday into the day on
Tuesday and bring our next round of rain and storms to the area.
Latest GEFS shows around a 30-40% chance of at least an inch of
rain mainly focused over northwest Iowa and adjacent areas. This
is a bit higher than other guidance, but appears to be the most
reasonable at this time given ensemble PWATs show anomalies
nearly of +1" in place as this system moves through. The
aforementioned trough over the Desert Southwest will absorb the
remnants of a Pacific Ocean tropical cyclone as it ejects to
the north and east during the middle to end of the next work.
This may help to keep a decent amount of moisture in place over
primarily northwestern Iowa into the end of the upcoming work
week, though at this point it looks like the heaviest rain
associated with this will stay south of the area.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1223 AM CDT Sun Sep 27 2026

A mix of conditions continue this evening with mainly IFR to
LIFR cigs expected this TAF period. Taking a look across the
area, IFR to LIFR stratus continue to expand this evening with
a few pockets of drizzle. While the drizzle is mainly occurring
along and east of I-29, we also starting to see areas of fog
develop across portions of southcentral SD. While these conditions
will likely persist through at least daybreak, could see some
of this activity carry over to mid to late morning until the
surface winds slightly increase. Either way, kept the drizzle
mention at both KFSD & KSUX through about 18z while adding a
more pronounced fog mention at KHON through around 16z. Lastly,
light and variable wind will become more easterly heading into
the early afternoon.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 10 AM CDT this morning for SDZ050-053-
     054-058>060-063>065-068.
MN...None.
IA...None.
NE...None.

&&

$$

UPDATE...JH
DISCUSSION...Samet
AVIATION...05