textproduct: Sioux Falls

KEY MESSAGES

- Isolated showers are possible (10-20% chance) over southwest Minnesota Friday afternoon. Wind gusts of 40 to 50 mph can't be ruled out with this activity. - More widespread rain risks return late Saturday into Sunday, though considerable uncertainty remains on the track of this system.

- Greatest severe weather risks continue to remain focused south of the Missouri River and Highway 20 corridor Saturday.

- Forecast rainfall totals vary significantly through Sunday, though greatest potential for excessive rainfall remains just south of the forecast area. Ensemble probabilities for >1.0" are around 20-40% near the Missouri River.

UPDATE

Issued at 846 PM CDT Thu Jun 18 2026

As the last shower over northern Iowa fades, a dry evening is in store for the area. Clouds over the northern High Plains will drift into the area through the overnight hours from west to east. Though winds turn light to calm overnight, these increasing clouds should keep fog development at a minimum. The exception is over parts of northwest Iowa mainly near and east of a Spencer to Storm Lake line where the clouds don't arrive until sunrise or slightly afterwards. This is where the better chances for fog reside, though probabilities are still quite low at around a 20-30% chance at this time. Another cool June night is ahead with lows in the low to mid 50s along the Missouri River Valley to the upper 40s to low 50s elsewhere.

The forecast for tomorrow remains largely on track, see discussion below for more details. One thing to note is that the chance for the diurnally driven, potentially gusty showers tomorrow afternoon have trended mostly east of the area into central and southeastern Minnesota with the latest guidance, but still can't be ruled out over parts of southwest Minnesota (10-20% chance).

DISCUSSION

Issued at 1247 PM CDT Thu Jun 18 2026

Still indications of some weak instability this afternoon, mainly over parts of southwest MN. This could generate a few showers, of which some gusty winds to 40 to 50 mph will be possible. This activity will be driven mainly by the heat of the day so should dissipate by about 9-10 pm.

A weak wave moves through Friday morning into the afternoon. The combination of a modest increase in moisture in the mid levels with weak instability above this moist layer, 700-500mb lapse rates about 7 degrees C, should allow for some ACCAS and showery activity during this time. If the clouds and mid level moisture can exit by mid afternoon, isolated diurnally driven showers may also pop up late afternoon into the evening. Impacts from this will be minor, but once again some gusty winds will be possible if some diurnally driven showers can develop with fairly unidirectional winds with height and fairly strong winds aloft.

Surface high pressure settles in Friday night into Saturday morning, which could result in a little patchy fog.The better chances look to be near the Big Sioux River Valley, but confidence is too low to include in the forecast.

Saturday should be a fairly pleasant day with increasing clouds and a fairly light easterly wind. Continued low humidity and highs mostly in the 70s.

Upper level low pressure rocks northward later Saturday night into Sunday morning. This lift will continue to fight the lower level dry air, but especially south of I-90 rain and very isolated thunderstorms will increase. With more confidence in this dry layer, rainfall amounts have trended downward.

Sunday into Monday poses more problems as the models disagree on handling the low pressure exiting. Rain chances should linger Sunday into Monday but confidence on where and especially amounts is very low.

AVIATION /00Z TAFS THROUGH 00Z SATURDAY/

Issued at 635 PM CDT Thu Jun 18 2026

Isolated showers that are located mainly north of I-90 to start the period will gradually diminish through the evening hours. Mid to high level clouds will gradually spread through the area from west to east as winds turn light to calm overnight. This increasing cloud cover should prevent most areas from seeing fog overnight, but can't rule out some patchy fog mainly near and east of a KSPW to KSLB line where clouds arrive last early Friday morning. Chances for this are low, around 20-30%.

Light showers also look to develop heading into Friday morning, but VFR conditions are expected to continue through the end of the period. Some thunder will be possible Friday afternoon mainly in southwest Minnesota and adjacent portions of northwest Iowa. Winds will increase from the west-northwest through the day Friday. Afternoon winds on Friday will gust to near 30 kts, highest over the higher elevations of the Coteau des Prairies.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...None. NE...None.