508 
FXUS63 KFSD 201652
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1152 AM CDT Sun Sep 20 2026

.KEY MESSAGES...

- The next better chance for rain will come tonight into Monday.
  Thunderstorms will be very isolated and severe weather is not
  expected, but localized rainfall totals in excess of an inch
  are possible.

- Below normal temperatures will persist through next week.

&&

.UPDATE...
Issued at 430 AM CDT Sun Sep 20 2026

Northeast flow has become a bit more mixy beneath the stratus 
layer early this morning, which has allowed for improvement in
visibility and slow increase in cloud base heights. While this
will limit extent of fog through the remainder of the night,
weak lift atop a deep stratus deck is still producing areas of
drizzle based on web cam imagery and spotty Trace-0.01" precip 
amounts on area METARs. Expect the potential for light drizzle 
to continue into the mid-late morning when this lift diminishes.
However, broader lift and even a shallow convective layer below
850MB will bring increasing chances for light rain to portions
of southeast SD into northwest IA by mid-late afternoon. 

Rain coverage is then expected to increase through tonight as a
broad mid-upper level wave slowly spins eastward across the 
region. HREF LPMM (Localized Probability-Matched Mean) indicates
a potential for a band of heavier rainfall, upwards of an inch
to locally over 2 inches. While the location is still somewhat 
uncertain, trends favor this band extending from portions of the
I-90 corridor in southeast SD, into the Highway 18 corridor in 
northwest IA. Latest NBM has caught on to this and has begun
trending QPF amounts upward from previous runs, though still
falling shy of an inch most locations. This may need to be
refined further by later shifts.

Otherwise, a cool and breezy day is on tap with highs mostly in
the lower 60s and northeast winds gusting near 25 mph at times
today.

&&

.DISCUSSION...
Issued at 1247 PM CDT Sat Sep 19 2026

The low levels remain saturated to near saturated tonight into 
Sunday morning which will keep the potential for fog in place, as 
well as patchy drizzle. Dense fog will again be fairly sparse, but 
some locations will see the visibility fall to a half mile or less 
at times.

Overall, Sunday looks to be a pretty dreary day with low level 
saturation deepening through the day. While the visibilities will 
likely improve a bit through the morning, stratus will remain fairly 
low and will not dissipate. As this low level moisture deepens, a 
weak wave will approach from the south and bring slightly cooler 
temperatures aloft and a bit more elevated moisture. This should 
allow for scattered showers to develop, but with only very weak 
instability thunder looks unlikely. As this wave rotates northward, 
a slightly stronger wave will move eastward through northern NE into 
northwest IA which should keep an expanding area of rain in place 
across the area. Given the placement of the upper level wave and the 
associated instability, parts of south central and southeast SD down 
the Missouri River will likely see the better chances for an inch or 
so of rain. The 12z Nam, RRFS and HRRR all paint these higher 
rainfall amounts near and south of I-90.

This wave slowly moves through on Monday, so expect to see showers 
slowly dissipate from west to east through late afternoon. Stratus 
will once again be difficult to shake as the push behind this wave 
is pretty weak and lighter northeast to east flow will be in place in 
the lower levels. Some hints in the soundings that clearing will be 
possible on Monday night, but with light winds and a moist boundary 
layer, fog will then become moire likely for late Monday night into 
Tuesday morning.

Tuesday and Wednesday will see some weak upper level ridging with 
afternoon temperatures likely only rising into the 60s. 

Wednesday night into Thursday a trough of low pressure will approach 
from the west and bring a chance for showers and isolated 
thunderstorms. Severe weather looks unlikely. For now the better 
chances will likely be west of I-29.

Temperatures should remain a touch below normal Thursday into Friday 
with some potential for spotty showers. Highs generally in the upper 
60s to lower 70s.

&&

.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.

&&

$$

UPDATE...JH
DISCUSSION...08
AVIATION...08