878
FXUS63 KFSD 160550
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1250 AM CDT Wed Sep 16 2026

.KEY MESSAGES...

- Very light rain, sprinkles, or drizzle will be possible
  Wednesday afternoon into the evening.

- Rain, potentially heavy, will be possible late Thursday night
  into Friday. While uncertainty remains on the axis of heavy
  rain placement, some minor impacts to rivers and streams
  could be possible.

- Near normal temperatures persist this weekend and into next
  week. Any precipitation chances are likely to remain light
  and non-severe through the weekend.

&&

.UPDATE...
Issued at 908 PM CDT Tue Sep 15 2026

Only change to the forecast tonight is the addition of a
slight chance of sprinkles along the Highway 20 corridor
through early tomorrow morning as some moisture and elevated
instability starting around 700 mb may allow for a few spots of
light rain to develop. A dry sub cloud layer should reduce most
of this activity to only sprinkles at the surface. Otherwise, a
surface high is moving across the region, keeping quiet
conditions with calm winds out there this evening. This should
make for a cool night overall for most of the area, with lows
ranging from the upper 40s northeast to the low to middle 50s
along the Missouri River Valley.

Clouds from a system to our south will help keep things warmer
in our southern areas, but clearer skies will make for optimal
cooling further north. However, a weak wave to our west will
send some mid level clouds into the entire area by the early
morning hours, and that will stop areas from reaching full
cooling potential. And so the coolest areas tonight will only
end up slightly below average for lows. As the aforementioned
high pressure system shifts east heading into tomorrow,
southeasterly flow returns and starts bringing back some low
level moisture into to the area. Increasing warm air advection
at 850 mb in particular during the day tomorrow will result in
some sprinkles to light rain and even a few spots of drizzle
from time to time. There also may be enough elevated instability
tomorrow late afternoon and evening for perhaps a few rumbles
of thunder near and north of Highway 14 in eastern South Dakota
and into southwest Minnesota, which are places closer to some
upper level support associated with a wave passing to our north.

&&

.DISCUSSION...
Issued at 1232 PM CDT Tue Sep 15 2026

THIS AFTERNOON:  Sunny skies continue Tuesday afternoon as dry air
filters into the region.  Temperatures will continue to rise into
the upper 60s to lower 70s.

TONIGHT: Most notable change tonight was to continually lower dew
points from the NBM guidance. Short term models have done a
better job capturing lower dew points through the region and
keep surface winds easterly through the overnight hours. These
winds will keep reinforcing the middle to upper 40 dew points
currently in the area. Mid-lvl clouds will gradually filter back
into the region after midnight, and may lead to some
stabilization of the diurnal temperature fall overnight.

WEDNESDAY: A generally quiet day is on tap for the region
Wednesday. By mid-morning the 850mb ridge axis will slide east
of the Tri- State area allowing gradual moisture advection
northward by mid-day. Soundings indicate a thickening low-lvl
moisture profile through the afternoon as weak warm advection
passes across the Tri-State area. This may result in widely
scattered very light showers through the afternoon and evening.
At times by the evening, a bit of patchy drizzle could also be
possible as ceilings remain quite low and there remains weak
warm advection at the top of the saturated layer.

THURSDAY-FRIDAY: The most impactful weather in the next 7 days will
take place Thursday night into Friday. Low-lvl moisture and weak
boundary layer flow may keep clouds around the area early Thursday
morning.  High pressure over northern Minnesota may limit the rise
in dew points early in the morning, again which may be a deviation
from the NBM or at least pointed towards the 25th percentile. If we
have quite a bit of cloud cover, then the persistent easterly winds
may prevent temperatures from reaching the middle 70s.

Models are in strong agreement that a progressive open wave exits
the Central Rockies and crosses the Dakotas Thursday night and
Friday.  This system will be very much like a late Fall to early
Winter system, bringing strong layered frontogenesis and elevated
instability into the Tri-state area after midnight.   Deterministic
models remain a bit variable with the northward extent of the 700mb
forcing, with the GFS notably further north than other solutions.
Ensemble based solutions are clustered fairly well with a corridor
of heavy rain near Highway 14, but AI based ensembles of the GEFS/EC
which seemed to pick up early location shifts last winter, are
supporting of a track somewhere between Highway 14 and along
I-90. Rainfall will be slow to leave the area on Friday, with
some gusty northerly winds by the afternoon. Areas near the
Missouri River and Highway 20 areas have the highest chance of
seeing some sun in the afternoon though the current temperature
forecast remains highly variable given track of rain.

Given the influx of moisture northward, rainfall forecast amounts
could rise sharply over the 24 hr period ending mid-day Friday.
Ensembles support a greater than 40% chance of more than 2" of QPF,
with 95 percentile data already as high as 2.50-3" wherever
this band of precipitation falls. As we begin to ingest more
higher resolution data sets, we`ll likely see these broad areas
of high probabilities focus better, but also see those higher
end values rise. With that said, the WPC "slight" risk of
excessive rainfall seems warranted, with AI based outlooks
suggesting higher risks may be possible if the forcing zone can
be determined. This rainfall, especially as you begin to pass
the 2-3" mark, could lead to some increases in local river
levels, as rainfall this month has been above normal and we`re
beginning to see better responses in levels after rain ends.

SATURDAY-MONDAY: The weekend will remain slightly unsettled as upper
troughing lingers over the Northern Rockies. Brief shortwave
ridging should allow most areas to dry out on Saturday, but
feature cooler than normal temperatures. An upper low then
drifts slowly southeast across the Dakotas into Sunday and
Monday. Initial indications suggest the greatest lift stays over
the western Dakotas on Sunday with rain chances returning again
by Monday.

&&

.AVIATION /06Z TAFS THROUGH 06Z THURSDAY/...
Issued at 1249 AM CDT Wed Sep 16 2026

A few spots of light fog have developed north of I-90 to start
the period, but drier air than yesterday should prevent this from
becoming widespread. MVFR stratus will move into the Missouri River
Valley by the middle part of the morning and move northeastward
through the afternoon, covering almost the entire area east of the
James River by the evening. IFR ceilings will also become more
prevalent late this afternoon into the evening hours mainly east of
I-29. Patchy drizzle will also be possible with any IFR cigs. The
stratus may begin to erode from west to east towards the end of the
period as winds just above the surface turn more northwesterly,
though confidence on the timing of this is low and thus kept
the stratus through 17.06Z at KFSD and KSUX.

Winds will increase out of the southeast through the morning hours
near and after sunrise. Highest wind gusts will be near and west of
the James, where occasional gusts to 20-25 kts will be possible.
Winds will then slowly decrease through the afternoon hours,
becoming light and variable this evening.

&&

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

&&

$$

UPDATE...Samet
DISCUSSION...Dux
AVIATION...Samet