textproduct: Sioux Falls

KEY MESSAGES

- Chances for showers and storms increase Thursday morning, continuing Thursday night into early Friday. Some storms may be strong to severe late Thursday into Thursday night with strong wind gusts to 65 mph and heavy rain the main threats.

- Overall beneficial rainfall is expected Thursday through Friday morning, with a 60-90% probability of at least 0.50 inches and a 30- 70% chance of at least an inch for the area. This rainfall could however lead to isolated flash flooding in urban and flood prone areas, so be sure to remain weather aware.

- Dry conditions and seasonable temperatures return for the weekend.

UPDATE

Issued at 908 PM CDT Wed Jul 29 2026

Thunderstorms have developed across the western part of the state this evening. These storms will push eastwards through the rest of the evening and overnight hours. The storms will be moving into an increasingly stable airmass characterized by dry air in the mid levels which will result in weakening the storms. Thus, no severe storms are expected but a weak storm to shower is possible around and just after daybreak tomorrow morning in locations west of the James River.

Depending on how long the cloud debris lasts from these morning showers on Thursday, it could keep high temperatures a bit cooler if these clouds stick around long enough. There is also a sign from some of the models that low level stratus could develop across parts of Nebraska and push into the area tomorrow morning as well. However, the models are somewhat consistent in showing clearing skies or at least breaks in the cloud cover west of I-29 to allow for sufficient destabilization to take place. Should this happen, high temperatures will warm to the 80s across the area with moist dew points in the upper 60s and 70s. With moist neutral lapse rates in place, no capping will be present. As sufficient surface heating is reached, a mid level wave will be pushing into the area, allowing for potentially more widespread convection to develop along an inverted trough/weak surface low. With the mid level low over the forecast area, vertical shear values will be mitigated. As of now, only, looking at deep layer shear values on the order of about 25 to 30 knots. Still sufficient enough to allow some storms to become strong to severe with damaging winds to 65 mph via water loaded downdrafts. Some better storm organization is possible as most of the hi-res models have storms growing into a line during the early evening hours. This line may have the best potential for damaging winds. Heavy rainfall remains on the table as well as precipitable water (PWAT) values remain in the 99th percentile of climatology. Thus flash flooding is possible with these storms. Especially if they train over an individual location or pass through urban areas. While the greatest chance for flash flooding and strong to severe storms will be waning heading into the overnight hours, could still see weaker storms persist through the overnight timeframe. Latest guidance is showing a potential wrap around/TROWAL like precipitation shield to develop on Friday and persist across locations mainly along and east of I-29 through the day on Friday before exiting the area Friday evening. All this to say that rainfall amounts remain on track between a half an inch to up to about an inch and a half across the entire area. Locally higher amounts up to and exceeding 4 inches remains possible in the heaviest storms as well. Although drought conditions persist across the area, this heavier rainfall can still cause flash flooding concerns so continue to monitor the latest forecast for the most up to date information.

DISCUSSION

Issued at 241 PM CDT Wed Jul 29 2026

Lines of cumulus clouds have developed near and south of the Missouri River Valley this afternoon. Without much upper level support to get storms going, we will need to rely on spots reaching convective temperatures to get storms to initiate. According to soundings, this will be around 95 degrees or so. Chances for storm development with this is low, but either way severe weather is unlikely given weak mid level lapse rates and weak shear. However, can't rule out a wind gust up to 55 mph in any collapsing thunderstorm if they even develop in our area in the first place. Otherwise another very warm and humid afternoon continues, with heat indices pushing 100 degrees at times especially west of I-29 into the Sioux City metro. Doesn't look like these 100 degree heat indices will be too widespread and dew points do look to drop off a bit more through the afternoon, so did continue to hold off on any heat headlines. However, it's still important to be hydrated and take some breaks when working or playing outdoors this afternoon!

Showers and storms over western South Dakota will be knocking on south-central South Dakota's door by daybreak Thursday; however, this activity will likely be weakening as it moves into the area. Additional showers and storms will likely develop as an upper level wave moves across the area and will likely have enough with it to break the cap in the fairly weakly capped environment. This morning activity is unlikely to be severe and should help limit full destabilization from occurring before any afternoon/evening activity develops. However, we will still likely see a line of stronger thunderstorms develop in the afternoon over central South Dakota and move southeastward across the area through the evening hours associated with a cool front. 65 mph winds and quarter sized hail will be the main threat with this afternoon/evening activity.

There is an alternate, but less likely scenario where we don't get much if any rainfall during the Thursday morning time frame due to a stronger than expected cap, allowing for more destabilization to occur. In this scenario, like shown in the 29.12z HRRR, a stronger line/MCS would develop in the afternoon and evening and bring wind gusts potentially up to around 65 mph. Trends will be monitored, so keep up to date with the latest forecast. A secondary wave and an upper level low will close off near the area Thursday night into early Friday morning, likely keeping general showers and thunderstorms continuing into the night. This will also lead to some flash flooding concerns Thursday afternoon into the night. Wet grounds from morning showers/storms will combine with the stronger afternoon storms and overnight storms to lead to some flash flooding concerns mainly in urban areas that see multiple thunderstorms. Rainfall totals through Thursday night/early Friday morning will be around a half an inch to 1.5", but localized amounts exceeding 4+ inches will be possible. Make sure to stay weather aware and keep up to date with the latest forecast!

After this next storm system passes, an upper level ridge will build into the area and help to keep us dry. And with northerly flow in place, high temperatures for Friday and Saturday will be a lot more pleasant with some areas especially on Friday having highs staying only in the 70s! Southerly flow returns again by Sunday, so we should start to see another warm up, though we should stay below heat advisory criteria even as highs warm back up to the middle 80s to lower 90s. The next appreciable rain chances will return Monday night into Tuesday as cold front moves into the area. It looks like there may be enough instability and shear for at least some severe threat, but uncertainty remains high at this time.

AVIATION /06Z TAFS THROUGH 06Z FRIDAY/

Issued at 1229 AM CDT Thu Jul 30 2026

Thunderstorms continue to slowly progress eastward across central and south central South Dakota. Think the storms will continue to weaken with eastward extent. That said, think KHON has a chance for seeing these showers and storms so have included a PROB30 group in their TAF. The storms look to weaken to just showers through the morning hours tomorrow. At the same time, latest satellite imagery shows a small area of IFR stratus that has developed across parts of south central Nebraska. Think this area of stratus will expand through the night and push northwards. Have added MVFR stratus to KSUX's TAF but trends in stratus will be closely monitored through the night. While some showers may persist into the afternoon hours tomorrow, another round of thunderstorms looks to develop during the afternoon and persist through the rest of the period. How the storms may track remains a bit uncertain, but have added PROB30 groups to all TAF sites for the last 6 hours of the period to account for this uncertainty. Additional MVFR to potentially IFR ceilings will also finish out the TAF period.

FSD WATCHES/WARNINGS/ADVISORIES

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