An eastward moving cold front resulted in a broken line of thunderstorms impacting portions of northwest Iowa during the evening of July 11. With only 1,500 J/kg of instability and weak shear, the severe thunderstorm risk was minimal, but the strongest cluster of thunderstorms produced isolated wind gusts up to 59 mph.
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The episode as NWS FSD wrote it up.
An eastward moving cold front resulted in a broken line of thunderstorms impacting portions of northwest Iowa during the evening of July 11. With only 1,500 J/kg of instability and weak shear, the severe thunderstorm risk was minimal, but the strongest cluster of thunderstorms produced isolated wind gusts up to 59 mph.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Sioux Falls, SD wrote its last area forecast discussion before the first event at Jul 11, 5:43 PM CST, 2 hours 42 minutes earlier. Its key messages:
Area Forecast Discussion National Weather Service Sioux Falls SD 643 PM CDT Fri Jul 11 2025 .KEY MESSAGES... - Wildfire smoke moving in behind a cold front this evening is reducing visibility below 3 miles at times. Additional wildfire smoke moves into the region tomorrow afternoon and evening, reducing visibility and air quality. - A low end (level 1 of 5) risk of severe storms develops by late this afternoon, as a cold front brings scattered thunderstorms southward into the region. The main threats with the strongest storms will be up to quarter sized hail, strong winds up to 60 mph, and heavy downpours. An isolated funnel cloud or landspout is possible, mainly along the cold front itself. - Temperatures cool Saturday, but heat and humidity build back in for Sunday through Tuesday. Cooler temperatures return for the middle and end of next week. - Thunderstorm risks return for Sunday through Tuesday, with some threat of severe storms possible. && .DISCUSSION... Issued at 309 PM CDT Fri Jul 11 2025 A few showers and weak thunderstorm persist east of I-29 this afternoon. Should see these showers and storms drift east/southeastward over the next couple of hours. At the same time, a cold front has pushed into the area from the northwest. This front will serve as the focal point for new showers and thunderstorms to develop on with convective initiation expected over the next 2 to 3 hours or so. Storms look to be initially discrete before some upscale growth leads to a broken line/cluster of storms. CAPE value will be sufficient at around 1,500 J/kg of instability but shear will be quite weak on the order of 25 knots or less. That said, still think an isolated chance for quarter size hail and damaging winds to 60 mph is possible. The other aspect to the storms is the potential for funnels or even a landspout. This potential is being driven from the vorticity along the front itself. Despite the fronts vorticity, LCL's are decently high at around 4,000 to 5,000ft so it may be a bit more difficult to any funnel to touch the ground. Any chance for storms will come to an end by midnight as the showers and storms push east of the area. Low temperatures will fall to the upper 50s to low 60s. High pressure will push into the Northern Plains on Saturday, delivering dry and quiet conditions for the area. 850 mb temperatures will warm to the teens aloft. Mixing these temperatures to the surface will result in high temperatures in the upper 70s and 80s. Dew points will lower to the 60s to low 60s, which will keep humidity values down to 30-60%, lowest west of the James River. Thus, Saturday will be a nice day though there could be some wildfire smoke both aloft and at the surface. Low temperatures will fall to the upper 50s to low 60s overnight. Sunday will be a hotter day as highs warm to the 80s to 90s, warmest west of the James River. Southerly return flow on the backside of the previously mentioned departing surface high. Dew points will moisten to the 60s to even up to about 70F. This will increase humidity values and also result in CAPE values up to 1,500 to 2,000 J/kg. Effective shear value will be sufficient on the order of about 30 knots but lift is questionable. A shortwave trough will reside east of the forecast area, providing upper level subsidence across the Northern Plains. However, a weak shortwave trough at 700 mb will push into the area. A weak surface trough will push through the area which could result in another chance for showers and thunderstorms. This potential is quite uncertain though given the weak forcing that is in place. As of now, the ensembles only show a low 10-30% chance for rainfall amounts to exceed a tenth of an inch throughout the day. Have left model blended PoPs at this time but trends will be monitored. Zonal flow sets up for the beginning of next week. This will promote broad southerly flow into the Northern Plains, promoting humid conditions across the area. High temperatures will remain near to above average in the 80s and 90s. With weak shortwave troughs passing through the upper level flow, chances for showers and thunderstorms are possible. As of now, it looks like storm chances will increase heading into Monday evening as forcing for ascent strengthens. This chance for storms will persist through Tuesday as a cold front passes through the forecast area throughout the day. Given sufficient instability and enough shear in place, this could lead to additional chances for showers and storms, some of which could be strong to severe. Machine learning guidance also supports this possibility as these models show about a 5-15% chance for strong to severe storms. Will keep an eye on this potential over the weekend. Rain chances look to continue for Wednesday and Friday next week as shortwave trough continue to track through the upper level flow. Details of these waves is uncertain at this time so have left model blended PoPs. In terms of temperatures, highs look to cool to near to below average in the 70s to up to about 80F. Lows will fall to the 50s and 60s overnight. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 630 PM CDT Fri Jul 11 2025 Watching showers/storms develop over northwestern IA into far southeastern SD and into northeastern NE. Not expecting impacts to the KFSD terminal, but if this developing line holds together, showers/storms are expected to move into the KSUX airspace after 01z. Showers/storms move southeast through tonight. An additional area of showers and very isolated lightning continue to move east through central SD. Given the weakening trend of this area as it moves toward the James Valley, will keep any -SHRA mention out of KHON. Have seen some wind gusts around 30 knots with the CAA this evening and these may continue into tonight. Otherwise, wildfire smoke is reaching the surface this evening behind the front, with a couple of hours of MVFR to upper end IFR visibility. Additional wildfire smoke aloft and at the surface moves in through the day Saturday, leading to reduced visibility and air quality. && .FSD WATCHES/WARNINGS/ADVISORIES... SD...None. MN...None. IA...None. NE...None. && DISCUSSION...Meyers AVIATION...SG
Hazardous Weather Outlook National Weather Service Sioux Falls SD 648 PM CDT Fri Jul 11 2025 IAZ001>003-012>014-020>022-031-032-MNZ071-072-080-081-089-090-097- 098-NEZ013-014-SDZ038>040-050-052>071-130000- Lyon-Osceola-Dickinson-Sioux-O'Brien-Clay-Plymouth-Cherokee- Buena Vista-Woodbury-Ida-Lincoln-Murray-Cottonwood-Nobles-Jackson- Pipestone-Rock-Dixon-Dakota-Beadle-Kingsbury-Brookings-Gregory- Jerauld-Sanborn-Miner-Lake-Moody-Brule-Aurora-Davison-Hanson-McCook- Minnehaha-Charles Mix-Douglas-Hutchinson-Turner-Bon Homme-Yankton- Union- 648 PM CDT Fri Jul 11 2025 This Hazardous Weather Outlook is for northwest Iowa, west central Iowa, southwest Minnesota, northeast Nebraska, central South Dakota, east central South Dakota, south central South Dakota and southeast South Dakota. .DAY ONE...Tonight. Wildfire smoke at the surface is leading to reduced visibility and poor air quality this evening. Conditions should last a couple of hours at any one location, with improvement later tonight. Isolated strong to severe storms are possible this evening into tonight. Hail to the size of quarters and wind gusts to 60 mph are the main threats. .DAYS TWO THROUGH SEVEN...Saturday through Thursday. Additional wildfire smoke at the surface and aloft returns Saturday. This will lead to reduced visibility and poor air quality, especially during the afternoon and evening hours. Use caution and limit time outdoors if sensitive to smoke. Thunderstorms, possibly some strong to severe, return Sunday through early next week. .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected at this time.
The Sioux Falls radar (KFSD), 156 km away, was scanning. The volume nearest the first event began at 02:23 UTC.
1 thunderstorm wind. Local standard time, as filed.
Thunderstorm wind gusts measured by a personal weather station at Webb.
After NWS Directive 10-1605, the rules offices file Storm Data by.
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NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 1287166.