000
FXUS63 KFSD 271145
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
645 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 /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 645 AM CDT Sun Sep 27 2026

Widespread LIFR-VLIFR conditions at the start of this period,
with dense fog roughly west through north of a KYKN-KFSD-KMWM
line and persistent low stratus throughout the region. Overall
the visibility should improve to VFR or lower end MVFR range by
15Z-17Z as fog diminishes and stratus slowly lifts. Areas of
drizzle may again accompany the fog/low stratus this morning,
but precipitation amounts are expected to be much lighter than
recent days.

Ceilings should likewise slowly rise into MVFR to locally VFR
categories this afternoon, and a shallow unstable layer may
allow spotty light showers/sprinkles to develop during the
afternoon to evening. Thunder is not expected at this time.

Low confidence toward the end of this TAF period, but some model
solutions point to a potential repeat of lowering ceilings and
perhaps patchy drizzle again developing after 28/06Z. Did not
introduce any sub-MVFR ceilings or drizzle at this time, but
later shifts will monitor potential and introduce if needed.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 10 AM CDT this morning for SDZ038>040-
     050-052>060-063>065-068.
MN...Dense Fog Advisory until 10 AM CDT this morning for MNZ071-072-
     080-097.
IA...None.
NE...None.

&&

$$

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