960
FXUS63 KFSD 300358
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1058 PM CDT Thu Oct 29 2026

.KEY MESSAGES...

- Low chance (20-25%) very patchy fog is may form late tonight
  into Friday morning. Mainly along river valleys and east of
  I-29.

- Showers and very isolated thunderstorms will be possible
  Friday night into Saturday morning, mainly near and east of
  Highway 81. Drizzle and spotty showers will be possible west
  of Highway 81.

- More widespread rain returns later Sunday night into Monday.
  The EC/GFS and Canadian ensembles suggest about a 40-70
  percent for more than an inch of rain.

&&

.UPDATE...
Issued at 845 PM CDT Thu Oct 29 2026

Broad surface high pressure settles over the southern Great Lakes
region overnight. Winds will become southeast around 5-10 mph. This
will likely preclude widespread fog formation, but patchy fog is
still possible along river valleys and east of I-29 where winds will
be lightest (20-25% probability). Any fog that does form will
quickly mix out after sunrise Friday. Overnight lows are
expected to fall to the mid 30s to 40s.

Tonight and through the day Friday a mid-level wave will slowly work
northeast into the region. As it approaches stratus will fill in
from south to north. This will work to limit highs in the 50s. Prior
to the arrival of the main wave periodic, light, WAA driven showers
may form along and south of Highway 18 beginning Friday morning.
These will be very hit or miss in nature, and areas to the north
will likely not see any precipitation during the day. By late Friday
afternoon the main wave pushes north into the region. Rain showers
will become more numerous and widespread as they move north
overnight and through most of the day Saturday. While severe weather
is not anticipated, a few hundred Joules of MLCAPE may be enough to
produce some lightning. Rain tapers off through the afternoon. There
remains disagreement in exact track of the wave, with the GFS
taking a more easterly track and the EC, CAN, and NAM a more
westerly track. This would impact who sees rain and how much. As
of this forecast, the highest totals will be along and south of
Highway 18, and may see a tenth to a quarter of an inch. North
of there, a few hundredths up to a tenth.

&&

.DISCUSSION...
Issued at 104 PM CDT Thu Oct 29 2026

Weak ridging aloft moves through the area tonight into Friday. This
will allow for an increase in south to southeast flow in the lower
levels. Models soundings point towards some possible patchy fog
again later tonight, but stratus should increase from south to north
late tonight into Friday afternoon. So for now not anticipating
widespread fog issues. Other than the increasing stratus through the
day, Friday should mostly be dry. By afternoon into the evening a
wave will rotate northward bringing slightly cooler temperatures
aloft above the increasing low level moisture. This should bring
some weak instability with maybe 200-500 J/kg CAPE and no real shear
to speak of. This the expectation will be for mainly scattered
showers with isolated thunderstorms. The better chances for showers
and isolated thunderstorms should be near and east of I-29 with
areas near and west of the James River possibly capped and seeing a
better chance for drizzle with roughly the lowest 5000 feet
saturated and weak lift moving through. For now rainfall amounts
look light with some spotty tenth of an inch or so possible.

Saturday the challenge will be trying to break through a fairly deep
stratus layer as weak upper level support gradually diminishes. For
now expect cloud cover the linger and temperatures to not reach
their full potential, likely topping out in the lower 60s in most
locations. Still mild for this time of year.

Saturday night into Sunday expecting mainly dry conditions as
saturation aloft diminishes and any weak instability is gone. Sunday
will likely see a resurgence of stratus ahead of the next wave coming
Sunday night into Monday. This should again keep high temperatures
mostly in the lower 60s.

Sunday night will see a surge of warm air advection in the lower
levels as low pressure deepens to the west southwest and an initial
wave races by to the northeast. Would not be at all surprised if we
see enough instability Sunday night into Monday morning to produce
a few thunderstorms as the band of strong warm advection moves
through. After this a few question marks on low pressure
development. With the jet still pretty strong and southwest of the
main trough, expect low pressure to deepen across KS/NE area, then
lift east or northeast into Tuesday. The low pressure movement is
fairly low confidence as the models are yet to agree upon how much
jet energy wraps around to the east side of the low, but if enough
does, we could see rainfall continue well into Tuesday. For now even
on the backside of this system it is a bit too warm for snow, so
thinking all rain.

If this system were to wrap up as much as the ECMWF suggests, a few
snow showers would be possible Wednesday into Thursday, but not a
lot of support from other models, so nothing more than something to
keep an eye on.

As for precipitation amounts, the latest GEFS is still bullish
bringing over an inch of rainfall to many locations, with a 50-60
percent chance in far southeast SD, northwest IA and northeast NE.
The latest AI model information leaning towards the lower side on
rainfall amounts which worked well with the rain event this past
Monday when many models (lower and hi res) and ensembles were
indicating a widespread 1-2.5" of rain and we saw something closer
to 0.50 to 1.25 inch rainfall amounts.

&&

.AVIATION /06Z TAFS THROUGH 06Z SATURDAY/...
Issued at 1057 PM CDT Thu Oct 29 2026

East to southeast winds will be light between 5-10 kts. Winds will
likely be too strong for fog to form. Still, HREF guidance indicates
20-25% probability some patchy fog may along river valleys and low
areas, especially along and east of I-29 where winds will be
lightest. Confidence in fog impacting TAF sites was too low to
include at this time.

MVFR ceilings and visibility will prevail for the first part of the
period. Looking at satellite a stratus deck resides over Nebraska
working northward. This will continue through the overnight and into
Friday afternoon, gradually lowering ceilings to MVFR and possibly
IFR. Near sunrise we will see light, scattered showers begin to push
into the area along and south of Highway 20. These will very
gradually move north through the day Friday. Late Friday afternoon
into the evening and overnight showers and possibly isolated
thunderstorms will become more numerous and widespread. These will
continue through the end of the period into Saturday morning.

&&

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

&&

$$

UPDATE...AJP
DISCUSSION...08
AVIATION...AJP