River Ice, Forecasting, and the Winter of 2016/17

The winter of 2016-17 saw extreme ice production and movement in the upper Mississippi River drainage, with multiple rounds of freeze-up and break-up ice jams that caused significant tributary flooding in multiple states across the upper Midwest. A late December rainfall event and subsequent thaw moved significant volumes of river ice and runoff in to the mainstem Mississippi River along the Iowa/Illinois border, within the Rock Island District of the US Army Corps of Engineers. Another cold snap in January generated additional ice and locked much of the ice from upstream in place within the lock and dam system between Dubuque and Keokuk, IA, leading to major flooding and significant forecasting challenges within the reach.

The National Weather Service is responsible for issuing public river forecasts and flood warnings, and works closely with the US Army Corps of Engineers to exchange data and forecast information, including anticipated regulation strategy of the locks and dams along the mainstem Mississippi. The complexity of last winter’s events and the extreme volume of ice in the system created greater than usual uncertainty in routed flows within the reach and further downstream.

Beside the impacts to public safety and property from river ice jam flooding, there are significant operational and economic impacts to the navigation industry in the middle and lower portions of the drainage. Corps reconnaissance and access to the latest ice conditions aided significantly in assessing ongoing risk. Additionally, remote sensing of channel ice and inundation, and other tools available at the North Central River Forecast Center were used to monitor and update river forecasts. Communication of uncertainty and exchange of information was crucial in messaging risk to both the public and interagency partners, and also for monitoring impacts to navigation downstream from impeded flow and volume locked in place as ice.