textproduct: Sioux Falls

KEY MESSAGES

- Moderate to Major Heat Risk today (all areas) and Wednesday (southeast) indicates a potential for heat-related illness for those without adequate cooling and hydration. Protect yourself against the heat and check on more vulnerable individuals such as the elderly, children and those with chronic illnesses.

- A Heat Advisory is in effect for most areas near and south of I-90 from 1 pm to 9 pm today as heat indices climb above 100 degrees. - A Level 2 and 3 out of 5 (Slight to Enhanced) risk for severe storms remains in place tonight. Initial storms bring a large hail threat toward central South Dakota and Nebraska in the early evening, transitioning to damaging winds up to 75 mph farther east late evening into the night. Isolated tornadoes are possible.

- While an isolated stronger storm may still develop in portions of northwest Iowa Wednesday afternoon, the threat of severe weather in our forecast area continues to trend lower.

UPDATE

Issued at 435 AM CDT Tue Jun 9 2026

Areas of fog have developed in the weak wind flow west of I-29 early this morning, with observations/web cams indicating very patchy dense fog. With sunrise in just over an hour, do not expect widespread dense fog to develop, but early morning travelers may encounter rapidly changing visibility during their commute.

Overall the forecast for today and tonight remains on track. Focus during the daytime hours will be on heat and humidity with a Heat Advisory remaining in place for most areas along/south of I-90. By early evening, the focus will shift to an increased risk of severe storms which is discussed in detail below.

By Wednesday, models continue with an eastward shift in the severe risk for our area, with perhaps a small window mid-late afternoon where an isolated storm in our far east (mainly Ida Grove to Spencer Iowa and east) could become strong enough to produce large hail/damaging winds before the cold front exits by 6 pm.

DISCUSSION

Issued at 254 PM CDT Mon Jun 8 2026

Low stratus has helped split our area temperature wise, with temperatures mainly in the 70s west of I-29; meanwhile near and east of I-29, we're in the 80s where less cloud cover has been today. These areas that have cleared out the stratus could see an isolated thunderstorm through the early evening where 1,500-2,000 J/kg of MLCAPE has developed. The better shear is west of this area, so severe weather chances look quite low through this evening. But if an updraft could maintain itself, 60 mph winds and half dollar sized hail would be the main threats. These storms should mostly be diurnally driven, so expect a weakening trend after the sunsets. Can't rule out some patchy fog tonight; but overall, a quiet night is ahead for us. A more active Tuesday night is expected, more on that below.

Rain-wise, most of the daytime hours Tuesday should be quiet. The main story will be the building heat and humidity. Any morning fog or low stratus should erode quickly, allowing for daytime heating to take off quickly into the afternoon. Look for highs to be in the 90s for the majority of the area, with dew points into the 70s over northwest Iowa, far northeast Nebraska, and adjacent areas of southeastern South Dakota. This will bring heat indices into the triple digits for areas especially near and south of I-90. For this reason, did go ahead and issue a heat advisory for portions of our area from 1 pm to 9 pm Tuesday. The best overlap of hot temperatures and higher dew points will be in the Sioux City metro where heat indices could be briefly as high as 105 degrees. Make sure to stay hydrated out there and take frequent breaks if you have to work outdoors or if you have any outdoor activities planned.

The heat and humidity will also prime the atmosphere for strong to severe storms heading into Tuesday night. An upper trough will begin to dig in from the Canadian Rockies and send waves of vorticity our way Tuesday into Tuesday night. Can't rule out a stray thunderstorm in the afternoon, but the better chances arrive in the evening as storms likely develop off to our west and then move through our area into the night. There will be plenty of instability even as we lose daytime heating Tuesday night, on the order of 2,000-3,000+ J/kg of CAPE. Bulk shear values won't be as impressive, around 30 kts or so, but this should be sufficient to maintain strong to severe storms. With the highly unstable atmosphere and soundings show some mid- level dry air, damaging winds look to be the main threat and could be as strong as 75 mph. Mid-level lapse rates up to 8.5 C/km and large CAPE profiles will lead to a secondary threat of large hail to the size of a hen egg (2 inches) or slightly larger. Lastly, tornadoes will also be possible especially in the evening as hodographs show some decent low level curvature in place and storms have a better chance at being rooted to the surface. The tornado threat will be maintained overnight as strengthening low level jet spreads into the area. With all modes of severe weather possible during the overnight hours, be sure to have a way for warning alerts to wake you up at night!

Storms look to push east of the area as a cold front starts moving into our area. Most guidance now pushes this cold front mostly east of the area by peak daytime heating, so the threat for severe weather continues to trend eastward for Wednesday. Will have to watch late Wednesday night/early Thursday morning as the main wave moves through the area as this could help develop some storms mainly near and south of Highway-20. Instability will be the limiting factor, but the potential for shear pushing towards 60 kts will mean any storms will be worth watching if one could even get going early Thursday morning. Looking ahead, cooler temperatures and continued broad, low-end rain chances will be maintained heading into the weekend as general troughiness remains in place. Instability looks fairly weak during this time frame, so severe weather chances look low. We will likely see cooler temperatures especially into early next week when highs in the 70s may start to become more widespread.

AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/

Issued at 645 AM CDT Tue Jun 9 2026

IFR-VLIFR visibility has developed in some areas west of I-29 early this morning with areas of fog, most prolific through the James River Valley. These conditions should quickly improve by 13Z-14Z with VFR conditions generally prevailing through sunset.

Scattered thunderstorm clusters will move east-northeast across the area after sunset into the early morning hours of Wednesday. These clusters will be capable of erratic strong to damaging wind gusts. Timing is still uncertain, but have tried to hone in on a 2-3 hour window of most likely impacts for the TAF sites. Impacts may vary by an hour or two either side, so continue to monitor later forecasts for updates.

FSD WATCHES/WARNINGS/ADVISORIES

SD...Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for SDZ059>071. MN...None. IA...Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for IAZ001-002-012>014-020>022-031-032. NE...Heat Advisory from 1 PM this afternoon to 9 PM CDT this evening for NEZ013-014.