760
FXUS63 KFSD 201842
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
142 PM CDT Sun Sep 20 2026

.KEY MESSAGES...

- Rainfall overspreads most of the area through tonight,
  gradually ending west to east on Monday.

- Rainfall amounts will average about 0.50" to 1.50" in most
  locations.

- Below normal temperatures will persist through next week, but
  gradually become more mild late in the week.

&&

.DISCUSSION...
Issued at 141 PM CDT Sun Sep 20 2026

Patchy drizzle remains possible late this afternoon into the evening
ahead of the incoming rainfall. The rain will move into the area
through the afternoon into tonight. Low pressure to the southwest
will swing saturation and lift aloft into the area this afternoon
with a dry slot working north towards the Missouri River. This seems
to suggest that the better potential for a more steady rainfall will
be closer to I-90 as the dendritic layer dries out south of I-90
during the evening, but remains saturated near and north of I-90.
Model soundings do hint at some weak instability near the Missouri
River which may help overcome the lack of saturation in the
dendritic layer during the evening and overnight hours, but the
rainfall would be more scattered in nature. If this weak instability
does not come to fruition, drizzle will be more likely towards the
Missouri River. Given how weak any expected instability will be,
thunderstorms are not expected.

As for amounts through tomorrow, model agreement is fairly high in a
swath of a half an inch to an inch and a half, focused near I-90 in
southeast SD, then east into northern parts of northwest IA. These
rainfall amounts are not expected to cause any flash flooding or
rapid rises along rivers.

Monday will see lingering showers across the area, with a more
focused area over northwest IA as the upper level low slowly moves
out of the area. Amounts will be lower through the day on Monday,
but parts of northwest IA could see a quarter inch of additional
rainfall. Otherwise Monday will be cool and cloudy with highs from
the upper 50s to mid 60s.

Monday night into Tuesday morning could see some fog with light
southeast flow and a fairly moist boundary layer.

Tuesday and Wednesday should both be dry and cool with highs in the
60s both days. Winds will increase on Wednesday with gusts around 30
mph possible near and west of the James RIver.

Wednesday night into Thursday will be the next better chance for
showers and thunderstorms. At this time severe weather and heavy
rain look unlikely.

Temperatures will rebound back to around normal Friday into next
weekend as westerly flow aloft develops. Periodic chances for
showers and thunderstorms are expected during this time.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1149 AM CDT Sun Sep 20 2026

Widespread MVFR and IFR conditions are expected through the
period. From about 18z to 21z, ares north of I-90 may see
periods of VFR conditions as the cumulus field breaks up and
then reforms. Patchy drizzle remains likely over mainly
northwest IA before afternoon mixing helps dissipate much of
this activity. Rain will develop across the area with the most
persistent rain likely closer to I-90 and then into northwest IA
this evening into Monday morning. Closer to the Missouri River
rain may lighten, but then drizzle will become more likely
later tonight into Monday morning.

&&

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

&&

$$

DISCUSSION...08
AVIATION...08