Sioux City, IA Weather

Key Messages

- Rain will continue off an on today into Monday night. The ensemble output, backed by the latest individual models indicates a 75-100% chance for 1" or more of rainfall from about I-29 west with about a 30-60% chance for more than 2" from south central SD into the James Valley.

- An active pattern aloft will lead to additional rain chances from Tuesday night into Wednesday.

Update

Issued at 238 AM CDT Sun Oct 25 2026

Late tonight through early this morning the area will mostly be between two waves, the weaker one exiting to the east and the somewhat stronger wave moving in from the southwest. As this wave lifts north today, the main focus will be on warm/moist advection and a general lack of instability. This lack of instability suggests that areas that lose saturation in the dgz will struggle to produce precipitation. A quick walk through the model soundings indicates that northwest IA will likely see the best chance to remain dry for the bulk of the day while areas near and west of highway 81 see the highest probability to remain saturated through the day with off an on rainfall.

A well agreed upon increase in warm advection in the 850-750mb layer occurs tonight, then gradually lifts north on Monday. Rainfall should be more widespread on Monday with the stronger forcing near and west of I-29. Northwest IA still looks to struggle a bit with saturation in the dgz, but this time it appears there may be some weak instability based around 850-900mb that may drive some showery activity.

Monday night will see the bulk of the strong forcing lift northeast, bringing a loss of saturation aloft, but some remaining in the lower levels, hinting that some drizzle could linger into the overnight hours. Some very weak instability could allow for isolated to scattered showers on Tuesday, but amounts will be pretty light.

As for rainfall, the higher amounts still look to be focused west of I-29. Some of the higher res data does shift the higher amounts closer to highway 81, but the bulk of the models and ensemble output continue to hint at the higher amount, 1-2.5", near and west of the James River, north towards De Smet and Brookings.

Discussion

Issued at 200 PM CDT Sat Oct 24 2026

Currents & Tonight: Another dreary day continues! Taking a look across the area, a brief break continues this afternoon as drier and cooler air filters in behind a cold front. This along with breezy northwesterly surface winds with gust between 25-35 mph has led to quite the chilly feel this afternoon with highs sitting in the upper 40s to mid 50s west of I-29 and the 60s to low 70s east of I-29. Expect temperature to continue their gradual decline from here. Otherwise, the intermittent showers resume from late afternoon onwards as southwest flow aloft helps additional pieces of energy lift through areas mainly west of I-29 through Sunday morning with mainly light accumulations. Lastly, given the increased cloud cover overnight thinking temperatures won't decrease as fast nor as far as the NBM thinks (mid 30s to low 40s). With this in mind, decided blend in some CONSshort into our MinTs slightly nudge up overnight temperatures into the low to upper 40s

Sunday-Monday: Looking into Sunday, another wet and dreary day is ahead as a subtle 850mb front stalls across our area roughly along a Wagner to Sioux Falls to Windom, MN line. With broad southwesterly flow firmly in place aloft, additional pieces of lift (dPVA) will stream into the warm air advective (WAA) regime along and northwest of this near-surface feature spurring intermittent showers throughout the day within the left exit region of the coupled jet. While mostly light accumulation are expected during this period, should see an uptick in coverage from late Sunday evening into Monday as additional lift arrives and WAA strengthen ahead of the inverted trough axis. Looking aloft, most guidance has the base of the mid-level trough gradually lifting into the Nebraska Pan handle by Monday morning then central and eastern SD by Monday afternoon/evening. While there some questions remains on where the heaviest accumulations set up, its worth nothing that NBM QPF has taken a noticeable northwest shift towards the better dynamics which are west of I-29.

As such, still thinking most areas receive accumulating rainfall through Monday. However, currently thinking the axis of 1+ inches sets up somewhere west of a Yankton to Sioux Falls to Slayton, MN line with the heaviest accumulations west of Highway 281. Everywhere east of this line could be affected by a bit more dry air leading to accumulations of a 0.50" of an inch or less. While not a drought buster, this system will provide beneficial rainfall for parts of the area over a 24-36 hour period. With this in mind, the flood concerns are minimal though some ponding will be possible in some urban and low lying areas. Lastly, expect the cooler conditions to persist for both days given the increasing rain chances with daily highs sitting in the mid 40s to mid 50s north of I-90 and low 50s to low 60s south of I-90.

Tuesday Onwards: Heading into the extended period, quieter conditions will temporarily return for the first half of Tuesday. However, additional showers could develop by Tuesday afternoon along and east of I-29 as a cold front swings through. From here, the quieter conditions should persist through at least Friday as solutions in long-range guidance begins to diverge. Lastly, expect daily highs to remain mainly in the 60s to low 70s with the warmest conditions across northwestern IA.

Aviation

Issued at 619 AM CDT Sun Oct 25 2026

While much of northwest IA will remain mostly dry after a few hit and miss showers early this morning, rain will gradually become more persistent through the day west of I-29. By tonight this steady rain will shift farther east to I-29 and into parts of northwest IA. MVFR conditions are likely within the rain, decreasing to IFR later tonight.