FXUS63 KFSD 211142

AFDFSD



Area Forecast Discussion

National Weather Service Sioux Falls SD

642 AM CDT Mon Sep 21 2026



.KEY MESSAGES...



- Rainfall and areas of drizzle continues early this morning.

  Although rain coverage will gradually diminish through today,

  areas of light drizzle may linger through tonight and perhaps

  into early Tuesday.



- Below normal temperatures will continue through mid-week, 

  then gradually become more mild late in the week.



- Additional rain chances return Wednesday night into Friday,

  but severe weather risks remain low.



&&



.UPDATE...

Issued at 450 AM CDT Mon Sep 21 2026



Main area of rain has shifted north of I-90 through the early

morning hours as a mid-level dry slot wraps into the southern

half of the forecast area. Thick low cloud persist beneath this

dry slot, however, and weak lift atop the moist layer will aid

in continued drizzle/light rain chances today. 



The upper low is slow to move east and while rainfall amounts 

will taper off, models are trending a little slower in bringing

rain/drizzle to an end altogether. Have extended low (20-30%)

pops through tonight and later shifts may need to consider if

drizzle will linger into Tuesday in some areas as low clouds 

persist.



The persistent cloud cover and occasional drizzle/rain chances

will keep temperatures on the cool side for these last couple of

days of astronomical summer with highs in the 50s today and near

60 on Tuesday. Autumn begins at 7:04 PM CDT Tuesday.



&&



.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 /12Z TAFS THROUGH 12Z TUESDAY/...

Issued at 641 AM CDT Mon Sep 21 2026



More of the same through the next 24 hours with widespread IFR

to locally LIFR ceilings and occasional MVFR-IFR visibility in

fog and drizzle/light rain. Models to indicate a brief glimmer

of hope for parts of the Highway 14 corridor to break out of the

low stratus for a few hours this evening, but any improvement to

VFR conditions looks to be short-lived as MVFR or possibly lower

ceilings move back in prior to midnight. 



&&



.FSD WATCHES/WARNINGS/ADVISORIES...

SD...None.

MN...None.

IA...None.

NE...None.



&&



$$



UPDATE...JH

DISCUSSION...08

AVIATION...JH