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2008 Parkersburg–New Hartford tornado

EF5 tornado in Iowa

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Through Tornado, Humidity and Jet stream

The tornado first formed south of Aplington, traveling through a series of farm fields. Minutes after forming, it grew into a large, wedge tornado, directly impacting the city of Parkersburg at EF5 intensity. The tornado devastated the south side of town, including the Aplington-Parkersburg High School, killing seven people. After leaving Parkersburg, the tornado crossed Beaver Creek before hitting a group of homes in northern New Hartford, once again at EF5 intensity. Multiple homes, including the Oak Hill Cemetery, were completely destroyed, killing an additional two people. The tornado attempted to occlude three times before dissipating southwest of Fairbank. In addition to nine fatalities, 70 people were injured during the tornado's 70 minute lifespan and 43 mile (69 km) long path across Butler and Black Hawk counties.

As of 2026, this is the most recent EF5 tornado to affect Iowa. It was also the most powerful tornado of 2008, being the only EF5 tornado.

Meteorological synopsis

On May 18, meteorologists identified a pattern indicative of severe weather. A large scale trough was predicted to move across the northern United States, with associated moisture return from the Gulf of Mexico and ample instability forming a classic plains severe weather setup.

By May 21, models showcased an increasingly strong and robust negatively-titled trough rapidly moving across the United States before slowly stalling through the central plains. A large ridge present was set to breakdown, allowing a strong surface front to move across the area as well. Moderate instability was already forming due to a deep forming moist-layer and warm air advection from the south. The National Weather Service indicated that the "Combination should be sufficient for a multiple-day threat for relatively widespread severe storms."

On May 25, notices for a moderate risk of severe weather were issued for northern Kansas, southern Nebraska, eastern Minnesota, northeastern Iowa, and western Wisconsin with a slight risk from Texas to northwestern Ontario. Watches extended along all the corridor and storms developed in four different areas including northern Texas, northern Kansas, central Minnesota and Iowa and southern Manitoba. As forecast, the strong trough would dig into northern areas of the CONUS. A stronger than forecast low-level jet began to transport ample moisture northward towards the interest area for severe storms, and as early as 12:30 pm CDT strong instability began to climb, as well as dew-points in the upper 70s. Models began to showcase a broken line of discrete supercells moving east to northeast, and with very little interference and a broad warm sector, the supercells would be able to take full advantage of the environment and become extremely strong.

At 12:43 pm CDT, the Storm Prediction Center identified through water vapor imagery that a rapidly moving and strong jet streak was approaching from Minnesota to Iowa. Supercells began to rapidly intensify by 3:50 pm CDT, prompting upgrades in watches. A cluster of strong supercells in northern Iowa began to both interact and intensify, merging into each other and forming a descending-reflectivity core over the southern cell's developing mesocyclone, a micro-scale interaction indicative of aiding in tornadogenesis. Simultaneously, low-level rotation on the southern supercell rapidly increased. Strong gravity waves may have also assisted in tornadogenesis amongst the supercell cluster.

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