textproduct: Sioux Falls

KEY MESSAGES

- Isolated to scattered thunderstorms are expected to develop during this afternoon and evening. Widespread severe storms aren't expected, but isolated pockets of 40 to 60 mph winds and up to quarter size hail may accompany stronger storms.

- All those with outdoor plans on the 4th should continue to monitor the forecast for the late afternoon through sunset.

UPDATE

Issued at 403 AM CDT Sat Jul 4 2026

Quiet conditions are prevailing across most of the CWA early this morning, with areas of fog with mostly minor visibility restrictions. We have seen occasional visibility down to 1/2 mile or less, largely in areas which received heavier rain over the past couple of days, and have issued a Special Weather Statement to cover this through 7-8 AM. Will continue to monitor and consider a Dense Fog Advisory if the lowest visibilities become more widespread.

Also watching a line of thunderstorms which has been building northwestward into our far southeast counties (Ida Grove to Storm Lake areas. Conditions do not support any severe weather threat, but the storms are moving very slowly, if at all. If rainfall rates become more robust than what we have seen thus far, will have to monitor for very localized flash flood issues. At this point, however, we have a long way to go before this is a concern.

As mentioned in the previous discussions, we are still looking at a chance for isolated to scattered storms developing this afternoon/evening as a weak shortwave slides across the region. While a washout is certainly not expected, any storm could impact outdoor 4th of July activities with lightning or brief downpours. Weak shear should limit the potential for organized severe storms. However, DCAPE of 1000-1500 J/kg would support isolated strong to severe wind gusts (40-60 mph). Moderately steep mid-level lapse rates could also support isolated hail up to quarter size in the strongest storms.

DISCUSSION

Issued at 246 PM CDT Fri Jul 3 2026

After this morning's storms, cloud cover has cleared across most of the area, allowing for more effective diurnal heating and airmass recovery to take place. There are a few boundaries around that could result in storm development this afternoon and evening. The first is a stationary front located near and north and west of the forecast area. The second is a new outflow boundary that was spawned from the morning convection across south central South Dakota has pushed southeast across the majority of the forecast area, now down to near Sioux City. The main effective boundary is currently sitting near highway-30. This last boundary will be the main driver of new thunderstorm development later this afternoon and evening as a shortwave trough currently ejecting out of the Rockies interacts with this boundary. The previously mentioned outflow boundary also looks to meet this effective boundary at the same time. Thunderstorms look to develop near to after 5 pm on this boundary. As storms develop, they look to be initially discrete with large hail up to 2 inches in diameter. Like the past few days, storms look to grow upscale into a line as the mean flow is mostly parallel to the effective boundary. Once storms grow upscale, damaging winds to 70 mph will become the main hazard. The remaining uncertainty resides in where storms will develop. Most of the latest guidance keeps the convection just south of the forecast area. A few models do bring storms into the highway-20 corridor so can't fully rule out any severe storm chances just yet. It will come down to how far north the boundary can return. Any flooding potential will also come down to the boundaries location as well. With mean flow generally parallel to the boundary, training storms are possible if the boundary can return far enough north. Should storms form in the area, the main timeframe will be from about 5 pm through roughly midnight. A few lingering showers are possible through the night.

High pressure begins to enter the area on Saturday, July 4th. Despite northerly flow across the area, remaining moisture will keep instability values up to about 1,000 to 2,000 J/kg. Vertical shear values will be weaker than what we have seen the past couple of days with magnitudes of 30 knots or less. A weak shortwave trough will push into the Northern Plains as an upper level ridge builds aloft. Latest REFS puts the highest chances (40-50%) over southwest Minnesota. With weaker shear in place, do not expect these storms to be strong to severe. However, brief heavy rain along with gusty winds and lightning are possible in any storm that develop. Stay aware if you will be out any about on Independence Day! Latest hi-res guidance also shows a weakening MCS moving from west to east. Only 1 or 2 models show this MCS making it into the forecast area. Thus, have low confidence in a low end MCS affecting the area at this time.

Upper level ridging continues to build across the western CONUS on Sunday. This will change the overall flow pattern to put the Northern Plains downstream of this ridge with northwest flow aloft. Synoptically, this will result in large scale descent and looks to keep conditions dry for the day. High temperatures look to remain seasonable in the 80s across the area.

The pattern quickly reverts back to nearly zonal for the bulk of next week. Weak shortwaves will push through the flow which could bring daily chances for showers and storms. Tough to say if any chance for storms could coincide with severe storms chances given how vertical shear look to be weak throughout next week. Confidence is not high enough to deviate from the NBM PoPs but something to keep an eye on going forward. Aside from rain chances, high temperatures look to remain seasonable in the 80s across the area. Dew points look to remain in the 60s to potentially low 70s which will keep the Summer time humidity going.

AVIATION /12Z TAFS THROUGH 12Z SUNDAY/

Issued at 643 AM CDT Sat Jul 4 2026

Recent rains have aided in the development of areas of fog early this morning, with IFR-locally LIFR visibility to start this TAF period. This fog is expected to diminish by 13-14Z, leaving VFR conditions for most of the period.

Scattered VFR cumulus develops midday-early afternoon, with a chance for isolated to scattered thunderstorms in the late afternoon and evening. Winds are generally expected to remain light (AOB 12kt) through the TAF period, however erratic stronger wind gusts will be possible in any thunderstorm activity.

FSD WATCHES/WARNINGS/ADVISORIES

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