textproduct: Sioux Falls

KEY MESSAGES

- If storms can develop this afternoon to early evening, an isolated severe storm could produce large hail up to half dollar size and damaging winds to 60 mph.

- Moderate to Major Heat Risk Tuesday (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 has been issued for most areas near and south of I-90 from 1 pm to 9 pm Tuesday as heat indices climb above 100 degrees. - Tuesday looks to bring the greater severe threat of the next 3 days, with a large hail threat toward central South Dakota and Nebraska in the evening transitioning to damaging winds up to 75 mph farther east late evening into the night. Isolated tornadoes are possible.

- The cold front triggering storms on Wednesday is trending faster, with the associated severe storm threat shifting east into mainly Minnesota and Iowa.

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 /00Z TAFS THROUGH 00Z WEDNESDAY/

Issued at 550 PM CDT Mon Jun 8 2026

Mainly VFR conditions with occasional MVFR conditions will persist this TAF period. Taking a look across the area, quieter conditions persist this afternoon with potential for a few isolated showers and thunderstorms mainly along and east of I-29. With this in mind, decided to keep a PROB30 group for KSUX since we're already starting to see some development. Otherwise, lighter winds are expected overnight to end the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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