textproduct: Sioux Falls

KEY MESSAGES

- Scattered strong to severe thunderstorms will develop and lift northeast into northeast NE and northwest IA during this evening. The strongest storms will be capable of damaging winds to 70+ mph and/or 2 inch diameter hail. The threat for severe storms will diminish between 1-3 am.

- 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.

UPDATE

Issued at 838 PM CDT Wed Jul 1 2026

For the most part still waiting for storms to develop across northeast NE and northwest IA. Isolated storms are ongoing at this time. Around 8 pm what looked like a quick storm merger near Oto allowed a brief tornado to develop. Rotation in the storm was minimal so likely was some kind of boundary ingestion in the updraft below the radar beam that allowed this brief spinup.

Otherwise, storms are still expected to develop in central to northeast NE and lift northeast later tonight. with about 2000 J/kg CAPE and 40 knots of deep layer shear a few severe storms remain possible. The main threats would be hail to the size of ping pong balls and wind gusts to 70 mph. The hail threat is somewhat muted due to the freezing level around 14000 feet AGL. If some brief training of echoes occurs, some 1-3" rainfall amounts in very localized locations will be possible.

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 /00Z TAFS THROUGH 00Z FRIDAY/

Issued at 630 PM CDT Wed Jul 1 2026

Showers and thunderstorms will develop in northeast NE and northwest IA this evening. Hail and strong winds are likely with the stronger storms. A few storms could reach parts of southeast SD to near the MN/IA border in northwest IA. Outside of the thunderstorms, mainly VFR conditions are expected. Some patchy MVFR fog will be possible but somewhat low confidence on just where.

FSD WATCHES/WARNINGS/ADVISORIES

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