textproduct: Sioux Falls

KEY MESSAGES

- Scattered strong to severe thunderstorms are possible late this afternoon and evening mainly near and east of the I-29 corridor. The strongest storms will be capable of damaging winds to 70+ mph and/or 2 inch diameter hail. A tornado or two cannot be ruled out.

- Beyond this evening's threat, concerns are growing for more widespread severe storms Thursday evening into Friday and again Friday into Saturday with one or more overnight storm complexes possible.

- Multiple rounds of rain and storms over the next few days, combined with recent rainfall, may lead to growing concerns of localized flash flooding and minor river flooding through the end of the week. - Above normal temperatures continue through the rest of this week and into the weekend, with humidity increasing daily. However, we'll remain below heat advisory levels.

DISCUSSION

Issued at 240 PM CDT Wed Jul 1 2026

Skies have mostly cleared out from last night's storms except over portions of northwest Iowa where clouds linger from remnant showers that moved through during the mid morning hours. This is also where a boundary is roughly located that will be the focus for stronger convection to develop late this afternoon into the early evening. The latest HRRR runs have been trending convective initiation farther west into northeast Nebraska, and this is likely because those areas have cleared quicker and have thus been able to destabilize more efficiently whereas clouds have lingered over portions of northwest Iowa. Latest mesoanalysis shows around 1500-2000 J/kg of MLCAPE that will increase into the afternoon in an uncapped environment. A weak wave will also move across the area and help develop showers and storms by about 4-5 pm. Due to the lack of CIN across a fairly large area, there is a chance that numerous thunderstorms quickly develop around the over the Highway 20 corridor of northwest Iowa and far northeast Nebraska. If we get numerous storms developing at once, storms may be competing for the strongest updraft and thus lowering the overall severe threat. But if convection remains more isolated, storms initially will be capable of 2 inch diameter hail and damaging wind gusts to 70 mph. A tornado cannot be ruled out if a storm can get rooted to the boundary. Storms will push eastward and grow northward through the evening and possibly merge into organized clusters which will enhance the damaging wind threat to greater than 70 mph as storms push into northern Iowa and southern Minnesota. These stronger storms will exit the area around midnight, but additional weaker showers and thunderstorms will continue to develop overnight over northwest Iowa along the boundary as the low level jet feeds more moisture into the area. The main threat with this would be if these showers/storms train over the same area, it could result in minor flash flooding.

Troughing over the western US will continue to send upper waves through the region heading into the day on Thursday and Friday. A very weak wave on Thursday morning may set off a few showers and storms along a boundary over eastern Nebraska and western Iowa, but guidance is in fairly good agreement that the more intense parts of this convection will remain south of the area. Heading into Thursday afternoon, daytime heating should result in the cap eroding especially over portions of south-central South Dakota, which may allow for isolated supercells to develop given the 40-45 kts of bulk shear that will be in place. With lapse rates around 7.5-8 C/km, large hail to 2 inches in diameter will be the main threat with these storms, along with 70 mph straight-line wind gusts. The tornado threat looks low, though there may be brief window in the early evening as these storms move east where the low level jet can help increase 0-1 km SRH before storms turn more elevated heading into the later evening hours. This afternoon supercell threat is a conditional one as overall forcing will be weak.

The main threat for severe storms will arrive overnight Thursday into Friday as a stronger wave ejects across the northern Plains towards Thursday evening and fires up isolated to scattered thunderstorms over western South Dakota. These thunderstorms look to develop into either an organized line or into a few linear clusters and then progress through our area from west to east during the overnight time frame. Due to the linear nature of these storms, damaging straight-line winds to 70+ mph will be the main severe weather threat with this round. If storms form into a few different clusters and trail one another (thus move over the same area multiple times), will also have to watch out of a threat for flash flooding Thursday night/Friday morning. Yet another wave moves through the area on Friday, which will likely form more strong to severe thunderstorms especially in the afternoon and early evening hours. Uncertainty in how storms evolve Thursday night and differences amongst guidance precludes details on the exact threats for Friday, but certainly keep up to date with the latest forecast especially if you have outdoor plans for the July Fourth weekend. Speaking of July Fourth, the day itself will feature another wave passing through the region; however, uncertainty remains high on where any storms develop. The 01.12Z GEFS keeps the best chances of rain near and south of the Missouri River Valley while the EC Ensemble keeps it east of the area. Bottom line, there will be at least a broad area of 20-40% PoPs in place especially heading into Saturday night until the spread in guidance can be better resolved. From Sunday onwards, the active upper pattern may relax a bit as upper ridging tries to build in over the intermountain West.

AVIATION /18Z TAFS THROUGH 18Z THURSDAY/

Issued at 1249 PM CDT Wed Jul 1 2026

Isolated to scattered showers and thunderstorms will redevelop late this afternoon and evening especially near and east of I-29. Storms will be capable of damaging winds, large hail, and possibly a tornado. The better chances of severe weather will be near and east of Minnesota/Iowa Highway 60. The threat for severe thunderstorms ends late this evening, with additional showers and isolated non- severe thunderstorms continuing to be possible overnight in northwest Iowa. Otherwise, patchy fog, some locally dense, will develop tonight as winds turn light over top the wet grounds. The better chance for fog will be just west of the edge of the clouds associated with the overnight storms, so there is a bit of uncertainty as to whether or not we'll get fog at KFSD given that the site will likely be either just west of those high clouds or under them. Still, there was enough confidence to include MVFR visibilities at the KFSD site early Thursday morning. Any fog should diminish after the 02.14 to 02.15Z time frame and lead to VFR conditions through the remainder of the period.

Winds will pick up a bit out of the southwest over northwest Iowa and southwest Minnesota through the early afternoon, but only gusting as high as around 20 kts. Stronger wind gusts will be possible in any thunderstorm that develops late this afternoon through the evening. Winds will turn light and variable overnight across the area, but then start picking up out of the southeast to end the period.

FSD WATCHES/WARNINGS/ADVISORIES

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