March 2019 Rapid Snowmelt, Heavy Rain, and Ice Jams Lead to Catastrophic Mid-America Spring Flooding and the Evacuation of the NWS Omaha, NE Office

Nebraska and Iowa are experienced when it comes to winter, ice jams, snowmelt, and flooding, however, the conditions that came together for the March 2019 event were historic and life-changing with long-lasting effects. The Governor of Nebraska, Pete Ricketts, called the flooding the “most widespread destructive natural disaster to hit Nebraska”. Prior to the commencement of flooding, rivers across Nebraska and Iowa were already elevated due to an abnormally wet fall, an early onset of winter with below normal temperatures, and more snow than usual in October-December. In eastern Nebraska, Omaha and Norfolk experienced their snowiest February on record and it was the second snowiest February in history for Lincoln. The snow and sub-freezing temperatures persisted into early March and resulted in excessive river ice growth with no snow melt. February was one of the 10 coldest on record, and there were three additional snow events in early March. By 10 March, the snow depth averaged between 4 and 16 inches with the snow water equivalent ranging from 1 to 4 inches. The frost depth of 17 inches was measured at the National Weather Service (NWS) in Omaha. From 12-14 March, an extremely strong low pressure system called a “bomb” cyclone brought heavy rain, much warmer temperatures and dense fog to eastern Nebraska. This storm system produced 1 to 3 inches of rain over the existing snow cover in eastern Nebraska. The rapid warm-up and snowmelt resulted in the river ice breaking up and at times forming into ice jams. The frozen ground was impermeable, leading to nearly 100% runoff. All of these hydrometeorological factors resulted in catastrophic flooding across central and eastern Nebraska, and portions of neighboring states.

The widespread simultaneous ice break-up, snowmelt, and heavy rain yielded disastrous impacts. All told, 75 of the 115 gages in the NWS Omaha hydrologic service area (HSA) reached flood stage. Of the 75 gages, 21 exceeded major flood stage, 23 crested in moderate flood stage, and 31 reached minor flood stage. Preliminarily, 31 of the NWS Omaha HSA gages logged all-time record crests. The Spencer Dam on the Niobrara River failed, sweeping away a local resident from his home. Five residents died due to the flood waters. Numerous levees and dikes were breached, overtopped, or failed. The U.S. Army Corps of Engineers, Omaha District reported 350 miles of levees on the Missouri, Platte, and Elkhorn rivers and tributaries experienced significant flood damage and 47 confirmed federal levee failures. These federal levees and additional private levee failures led to several communities being impacted by the flooding and forced evacuation of thousands of residents. Offutt Air Force Base sustained $420M worth of damage with one-third of the main runway under water and damage to one-third of its buildings. During the event, the NWS Omaha declared a Level II Emergency per the Continuity of Operations Plan and was forced to evacuate the office. Two thousand miles of state roads and fifteen state highway bridges were damaged or destroyed. The Nebraska Governor estimated $1.3B in damage with 104 cities and 81 of 93 counties included in the disaster declaration. The Governor of Iowa estimated $1.6B of damage due to flooding with 56 of 99 counties included in the disaster declaration. Major roads and bridges remained closed for months. Nearly 600 homes were declared uninhabitable in nearby Omaha, Nebraska suburbs, with many more in surrounding communities.

This poster will focus on the hydrometeorological conditions that led up to this catastrophic event, the extensive impacts, and lessons learned in predicting and messaging an extreme flood event.