Northwest Iowa Tornadoes (May 1)

Multiple tornado reports occurred on May 1 in northwest Iowa between 6:50 and 7:45 PM. The tornadoes occurred through Lyon and Sioux counties, near the towns of Rock Rapids, Sioux Center and other nearby towns such as Doon, Inwood, and George. The NWS in Sioux Falls has conducted a survey of the tornadoes, a total of 5 occurred in Sioux and Lyon counties. The longest and strongest tornado is one that began just north of highway B30 west of Carmel, IA and continued to the north/northwest passing just to the west of Rock Valley and finally lifted just south of highway A42, southeast of Inwood. This tornado which featured a path of nearly 13 miles and width of damage of up to 500 feet was rated an EF2 with winds 111 to 135 mph. More information and maps of the path and damage locations can be found on the Sioux Falls NWS Survey Page. In addition, the NWS in Sioux Falls has posted a summary of the events along with a few synoptic reviews as to what occurred in Sioux and Lyon counties.

NWS May 1 Tornadoes & Severe Weather Review

One storm chaser was on this storm and captured the entire life of at least two of the tornadoes, including the large tornado near Rock Valley, IA. Van DeWald, the storm chaser from Omaha, NE made the trip and was the one who captured the images that can be found on his Chase Account Page. He also had a video camera going, in which the video can be found on youtube: Video of the Rock Valley Tornado on May 1, 2008 (~7 PM)
Video copyright Van DeWald

Several pictures from local residents of the tornado and subsequent damage can be found on the KTIV weather blog. A few other pictures from locals can be found throughout the internet, some quick links to some via blogger uploads: Image 1, Image 2, and Image 3.

Other news sources have received some great video and pictures from locals as well. KELO out of Sioux Falls has three public videos that have been uploaded to their website, you can view them here.

The tornadoes from May 1 are unique in the way that they often appeared to be occurring underneath fairly weak showers and thunderstorms. In some cases appearing where there was little reflectivity present on the radar. Some initial statements are accounting these as landspouts, or essentially a tornado that is not associated with a thunderstorm's rotation. Early indications do show that there was strong rotation on KFSD radar, at least at the lowest level. I will be looking into the storms to see how extended this rotation was into the storm, but currently FSD NWS is calling these tornadoes instead of landspouts. I will post any future information on my findings in the coming days here...

8:00 AM May 2 Update: I've updated the post above with a few more screen grabs from Van DeWald's video camera and the video that he captured.
Also have a few images via KTIV that local residents sent in last night and this morning that were added.

May 2 Afternoon Update: Rearranged the post a bit, included new information and added in a link to the Sioux Falls NWS page they have about the event. Also more local images and video links were added.

5:30 PM May 2 Update: The Sioux Falls NWS has completed their survey of the tornadoes in northwest Iowa, this information was added to the page.