textproduct: Sioux Falls

KEY MESSAGES

- Strong to severe thunderstorms have already developed along and outflow boundary this afternoon. Large hail up to 2+ inches and damaging winds to 70 mph are the main hazards with these storms. A tornado or two is possible as well.

- A second round of storms is expected this evening and night near and south of I-90. These storms look to form into a line and be capable of damaging winds to 75 mph. An isolated line embedded tornado is possible as well.

- Another round of strong to severe storms is possible Friday evening and night. This second round of storms again looks to come in the form of a line. As of now, these storms look travel along the Missouri River Valley with damaging winds to 70 mph being the main hazard.

- With multiple periods of thunderstorms in the region, flooding becomes a concern for any locations seeing multiple rounds of heavy rainfall. A Flood Watch has been issued for all of northwest Iowa through Friday morning.

- While severe weather is unlikely on July 4th, isolated to scattered showers and storms are possible.

DISCUSSION

Issued at 245 PM CDT Thu Jul 2 2026

A complex convective evolution is expected for the rest of today, including the evening and overnight hours, as multiple boundaries will be in play. An outflow boundary from storms in North Dakota has pushed into the area near and south of highway-14 corridor early this afternoon. Thunderstorms, some of which are strong to severe already, There is also a second boundary near I-90 that served as the focal point for this mornings storms.

The first round of storms have already fired along the first outflow boundary from the North Dakota storms. These storms look to affect locations north of I-90, but especially along and near highway-14. These storms will be in a favorable environment characterized by effective shear values up to around 40 knots. Hodographs show a little curvature in the lowest 0-3 km. But the bulk of the shear will remain aloft as the right entrance of an upper level jet streak begins to push off to the northeast. CAPE values will be more than sufficient with MLCAPE values up to and exceeding 2,500 J/kg. DCAPE will also be sufficient near to above 1,000 J/kg. Thus, Large hail up to 2+ inches in diameter and damaging winds to 70 mph will be the primary hazards. A tornado or two is also possible should a storm ride along the outflow boundary and efficiently ingest it's helicity.

This round of storms will be coming to an end by the later evening hours. However, another shortwave trough will be pushing into the area, developing a second round of storms along the second boundary. This second round looks to grow upscale into a mesoscale convective system (MCS) and push eastwards across locations generally near and south of I-90. With the upper level jet pushing away from the area, overall vertical shear profiles will be beginning to weaken. However, the low level jet will be strengthening which will allow the MCS to maintain its strength through the overnight hours. Plenty of elevated instability will be availability in excess of 1,000 to 2,000 J/kg. Vertical shear values will remain sufficient at 40 knots. 0-3 km shear will be a bit on the weak side with magnitudes up to 20-25 knots. This shear vector may be oriented perpendicularly off of the MCS which suggests that a tornado threat is possible. Though this will depend on how the storms and their respective orientation play out. DCAPE values will remain near 1,000 J/kg but min to max theta-e difference value's will be low, down to about -25K. Thus, damaging winds to 75 mph will be the main hazard.

Another round of storms is possible for the day on Friday. With the previously mentioned shortwave trough east of the area, the daylight hours for Friday look to be on the drier side due to subsidence on the backside of the departing wave. Some isolated showers may persist though. The next chance for strong to severe storms will come on Friday evening and night. As of now, the latest hi-res guidance is showing another MCS tracking near to down the Missouri River Friday night. The environment looks to be more than sufficient with instability values up to 2,000 to 3,000 J/kg. Effective shear values up to 40-50 knots will coincide with the larger instability. 0-3 km shear will be stronger at 30-35 knots. Like Friday's storms, there is some uncertainty regarding the orientation of the 0-3 km shear vector. If a proper orientation can be achieved, then a line embedded tornado threat can develop. Min to max theta-e difference will again be sufficient, down to around -25K. This will support the potential for damaging wind gusts as the MCS passes through. gusts may exceed 70 mph. Golf ball size hail could be possible in the initial developmental stage before a quick transition to a linear mode occurs. There remains uncertainty regarding the location of this potential MCS as its overall evolution will be dependent on how Thursday's storms pan out. Any severe storm threat should be coming to an end near daybreak Saturday morning. Aside from the severe storm potential, there remains the potential for flash flooding with them as well. Please see the hydrology section below for more information.

Saturday (Independence Day) looks to have some storm potential. An incoming surface high pressure system looks to push some of the available moisture to the south of the area. While this does not mean there will be no instability, it does suggest that the strongest storms will be off to the south of the as the best frontal forcing looks to lie near or south of I-80. That said, non-severe storms are possible which could affect holiday plans. Too early to say for sure when and where these storms could track. Continue to monitor the latest forecast for the most up to date information.

The rest of the weekend and first half of next week could feature additional chances for showers and storms. This potential is uncertain at this time as the better upper level jet will push away from the Northern Plains, leaving weaker forcing for this period of time. As of now, have not strayed the NBM's PoPs at this time. Otherwise, temperatures look to remain in the 80s to potentially reaching into the low 90s in a few spots.

AVIATION /18Z TAFS THROUGH 18Z FRIDAY/

Issued at 1241 PM CDT Thu Jul 2 2026

Latest satellite shows remnant cloud cover across areas along and east of I-29 early this afternoon. A few showers remain along and north of highway-20. An outflow boundary is also present mainly near KHON. This boundary looks to serve as the focal point for new thunderstorm development this afternoon around KHON. These storms will push off to the northeast through the afternoon and evening hours before another round of thunderstorms develops late this evening and overnight. The bulk of the storms looks to affect locations mainly south of I-90. These storms will push east of the area by the morning hours tomorrow. Ceilings and visibilities look to fall to MVFR levels or lower in the storms themselves. Additional showers could pass through the area during the morning hours tomorrow but confidence is not high enough to include in a TAF at this time.

There remains uncertainty regarding the exact location and timing of storms. Changes in the forecast in the next TAF update as well as amendments are possible.

HYDROLOGY

Issued at 245 PM CDT Thu Jul 2 2026

Individual model guidance, along with PMM from the HREF continues to indicate the potential for 1-3 inches of rain with pockets exceeding 4 inches in some locations. This, combined with saturated ground from recent rainfall, may result in enhanced runoff. Confidence remains low in the exact location or areal extent of higher rainfall but there appears to be agreement in a west to east stripe of enhanced rain totals across NW IA this evening and overnight that would be capable of flash flooding. This idea has some support from NWM rapid onset flooding probabilities. In addition to flash flooding, guidance would also suggest some minor to perhaps moderate river flooding is also possible by this weekend.

FSD WATCHES/WARNINGS/ADVISORIES

SD...None. MN...None. IA...Flood Watch through Friday morning for IAZ001>003-012>014- 020>022-031-032. NE...None.