textproduct: Sioux Falls

KEY MESSAGES

- Patchy dense fog is possible tonight. While the best chances are east of I-29 (40-50%) patchy valley fog is possible as far west as the James River Valley. Fog should burn off by mid to late morning.

- Periodic chances (20-60%) for showers and thunderstorms continue this week. Details remain uncertain at this time.

- Thursday and Friday Elevated to near Critical Fire Danger is possible, due to gusty winds and low relative humidity.

UPDATE

Issued at 901 PM CDT Mon Apr 13 2026

Showers and thunderstorms have pushed east of our region. Mostly quiet conditions are expected overnight as winds become light and variable. Short term guidance indicates about a 40-50% chance of patchy dense fog development after midnight tonight. While the highest chances for fog are east of I-29, very patchy valley fog may form as far west as the James River Valley. Fog should burn off by mid to late morning. Slightly cooler highs in the upper 60s and 70s Tuesday thanks to CAA behind the departing low pressure. Winds will be slightly breezy out of the north gusting 15-20 mph. While relative humidity values will remain above critical thresholds, High Fire Danger will still be present over south central South Dakota Tuesday afternoon. Please continue to use caution and report any fires immediately.

By Tuesday afternoon a wave approaches from the west bringing chances for isolated to scattered showers and thunderstorms. These storms are not expected to be severe and will be very spotty in nature. Most will not see any rain during the day Tuesday. Tuesday evening the surface low approaches from the southwest reinvigorating shower and thunderstorm chances. The better dynamics lay to the southeast of our forecast area, but a few stronger thunderstorms are possible east of I-29 Tuesday evening into Wednesday morning. Shower chances hang around through much of the day on Wednesday before clearing out Wednesday afternoon.

DISCUSSION

Issued at 238 PM CDT Mon Apr 13 2026

Scattered thunderstorms are set to develop over the next few hours, bringing the potential for a few severe storms with large hail, damaging winds, and perhaps a tornado or two. As of 2 pm, a surface low is located over northern Nebraska with a warm front extending northeast of it across far southeastern South Dakota into northwest Iowa. Dew points in the 60s have been gradually spreading northward, and these higher dew points are expected to reach the I-90 corridor over the next couple of hours. This boundary will be the focus of initial storm development, with these storms having access to 35-50 kts of effective bulk shear and 1500-2000 J/kg of MLCAPE. There are questions though on how much some high clouds have limited the area from reaching full heating potential, but if a storm can get going then steep mid level lapse rates of 7.5-8.5 degrees C/km and mostly straight, elongated hodographs will favor large hail to around 2 inches in diameter or larger. The secondary threat will be damaging wind gusts up to 70 mph. If a storm can get rooted to the aforementioned surface warm front, then a tornado or two will also be possible. Can't rule out a strong tornado either, primarily over southwest Minnesota. As the low pressure system drift across the area, a few additional showers and storms look to develop farther south across northwest Iowa (down to about IA Highway-3, or just north of US Highway-20) within the warm sector around sunset. These storms could also be on the strong to severe side, with an isolated instance of quarter sized hail and 60 mph as the threats.

Showers and storms will exit off to our east by the mid evening hours, leaving mostly quiet conditions in its wake. A few showers may develop in central South Dakota prior to daybreak Tuesday, but dry air should win out and prevent most if not all of this from reaching the ground. Patchy fog will also be possible by early Tuesday morning across portions of northwest Iowa and southwest Minnesota as winds turn light and variable overnight and ample moisture remains in place. Temperatures tonight drop mainly in the 40s, though some 50s are possible in our easternmost areas. Low chances for showers continue into the day on Tuesday, but activity is expected to remain spotty at best as rain continues to battle a dry sub cloud layer. Highs will range from the 60s northwest to 70s southeast. Rain chances look to increase Tuesday night into Wednesday as two shortwave troughs impact our area. The best chances of rain and storms look to be over northwest Iowa and adjacent areas of Nebraska, South Dakota, and Minnesota. At this time, severe weather looks unlikely with this system as the better instability looks to be off to our south and east.

Rain and storms exit off to our east by Wednesday night, leading to a dry Thursday. Winds look to increase on Thursday especially west of I-29 closer to a deepening surface low, and winds may take on a southwesterly component especially in south central South Dakota. This could lead to another day with higher fire danger as temperatures will be warm and relative humidity values drop to 25% or below mainly along and west of the James River. Still some uncertainty into how breezy the winds will be, so keep up to date with the latest forecast. Not too much time to look into the extended forecast given the near term severe weather threat, but guidance is in fairly good agreement that the western trough will begin to move into our area by the end of the work week/early weekend. This could bring more rain and storms to our area on Friday and then colder weather into Saturday as guidance indicates a stronger push of cold air advection behind this system.

AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/

Issued at 1156 PM CDT Mon Apr 13 2026

Mainly VFR conditions with occasional MVFR to IFR vsbys are expected this TAF period. Taking a look at satellite imagery, most clear conditions persist tonight. While these conditions should persist for the next few hours, developing fog across northwestern IA and potentially our River Valleys could lead to occasional MVFR to IFR vsbys especially as locally dense patches develop. Otherwise, should any fog gradually erode by mid-morning on Tuesday. Light northerly to northwesterly winds will persist for most of the day. Lastly, a few light sprinkles to showers will be possible near KHON by Tuesday afternoon. However, confidence is too low (<30%) to include in the TAF at this time.

FSD WATCHES/WARNINGS/ADVISORIES

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