textproduct: Sioux Falls

KEY MESSAGES

- Thunderstorms will continue along the Missouri River and into portions of northwest Iowa into daybreak. 60 mph winds, ping pong ball size hail, and torrential rainfall will be the greatest risks.

- Extreme uncertainty remains in Friday's forecast. Another round of strong to severe storms is possible Friday afternoon and night. All hazards may be possible, including strong straight line winds in any line of storms that forms.

- 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 into northeast Nebraska through Friday morning.

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

UPDATE

Issued at 1237 AM CDT Fri Jul 3 2026

TONIGHT: Convection continues to develop along periphery of low-lvl jet convergence near the Missouri River and into the Highway 20 corridor areas. Soundings suggest most of this activity is lifting off of the 800 mb layer with generalized west to east motion through the remainder of the night. Strong moisture transport into the Missouri River valley and Highway 20 corridor, and slow storm motion AOA 10-15 knots may promote an increased risk for flash flooding through daybreak. Have expanded the flood watch into NE Nebraska where recent WOFS guidance indicates 20-30% probabilities for more than 3" of rain and ensemble max guidance suggesting 5"+ rainfall amounts could be possible. Most of this convection will ride along the edge of the effective shear axis, so while instability of 1500- 2000 MUCAPE will remain, severe risks remain more questionable as storm clustering and merging may lead to too much competition for persistent deep and sustained updrafts. Further west, we'll keep an eye on another wave moving through the western Dakotas, which is slowly crawling eastward but does have some potential to remain strong as it reaches the MO river valley. However the atmosphere has been fairly worked over in the past 12 hours so any additional development on the 800:700 mb layer may likely stay below severe limits but should be monitored for lingering gusts.

FRIDAY: The forecast for Friday is, well, very uncertain. Most CAMs and other deterministic models have struggled significantly to resolve even the initialization hours in the past day. That said, a few different scenarios could play out. The convection driven by the wave out west may slowly cross the CWA in the morning, keeping temperatures lower through mid-day and potentially lowering the severe weather risks. In this scenario the overnight convection along Highway 20 could also push the effective front far enough to the south to push afternoon/evening redevelopment away from us.

Another scenario would be a bit more troublesome if there is less lingering convection during the morning hours and the effective boundary to our south isn't driven that far away. Strong diurnal heating and some early day height rises could push that effective boundary further north, creating the potential for significant severe convection to form over the Central Dakotas and then plunge east southeast as a large MCS. This scenario could bring another day with all hazards expected, and high end wind gusts.

The end solution might be somewhere in the middle of this, with morning convection allowing some renewed strong convection by mid- day, and then we have an earlier than normal severe weather risk, and perhaps more limited in coverage, through the MO River valley. Given all this uncertainty, it will be vital to monitor the conditions through the day.

The forecast for the 4th of July remains favorable and should remain dry for most of the day. There remains a non-zero chance for a few late day showers/sprinkles to form and move southeast in the evening. However wind are very light into the overnight hours.

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 /06Z TAFS THROUGH 06Z SATURDAY/

Issued at 1226 AM CDT Fri Jul 3 2026

Conditions near KHON have improved with BKN clouds. Thunderstorms continue to develop along the Nebraska and South Dakota border and track slowly eastward. There is a slight chance these storms move into KFSD bringing higher winds, small hail, frequent lightning and low visibility. Best chances are in KSUX where thunderstorms are developing just west of the site.

The main area of storms push into KSUX over the next several hours bringing low visibility, lightning, potential for hail, and erratic winds. Conditions start to improve post 12-15z, with lingering shower chances. Another round of thunderstorms around the 17z-19z time frame for each of the sites, with clearing near the 23-02z timeframe.

HYDROLOGY

Issued at 245 PM CDT Thu Jul 2 2026

Thunderstorms continue to track along the Missouri River and into portions of northwest Iowa early this morning. Rainfall potential of 1-3" with pockets of up to 5" may be possible based on HREF and WOFS guidance with rainfall rates up to 3-4" per hour also possible. With this in mind, have extended flood watch into northeast Nebraska to account for an increased flash flood risk.

This rainfall, combined with saturated ground from recent rainfall, may result in enhanced runoff. 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 until 7 AM CDT this morning for IAZ001>003-012>014- 020>022-031-032. NE...Flood Watch until 7 AM CDT this morning for NEZ013-014.