Source: The Atlantic/Herschel Talley / Nebraska National Guard / Handout via Reuters
The State of Nebraska, along with several nearby states, is slowly recovering from one of the most extreme flooding events in recent memory. According to USA Today, the estimated losses across the entire Great Plains region now falling somewhere around $1.5 billion
These losses include everything from agricultural operations to residential properties, as the Missouri and Mississippi Rivers, along with several other rivers along their basins, struggled to keep up with the amount of water flowing through them. As the cleanup continues along some parts of the Great Plains, others are still experiencing flooding issues as flood waters descend all along the region’s watersheds. Many questions have been raised in the days following some of the worst observed flooding conditions, including why it was that conditions deteriorated to such an extreme point. Essentially, it was the overlap of several meteorological events that aided in turning this flooding event in particular into one for the record books.
We begin by first exploring a bomb cyclone, which typically refers to any low pressure system that has experienced bombogenesis, a process in which the central pressure of a cyclone drops 1mb per hour within the span of a 24-hour period. And while these cyclones tend to develop primarily in the ocean, they can develop inland at times, as was the case with the Great Plains bomb cyclone of March 2019.The entire region, especially the high and northern Plains, all experienced everything from blizzards to strong winds and torrential rains.
Source: NEXRAD Imagery
Then there are low-level jets, or LLJs, which similarly develop whenever a strong pressure gradient is experienced in the Great Plains as divergent upper-level air masses are transported by an upper-level disturbance, or wave, into an area of strong low-level convergence. In other words, as the pressure drops over the region the airmass overhead allows for air to speed up while air closes to the surface reacts by ascending to fill the void. When air parcels from the Gulf of Mexico enters these sorts of wind motions, their water content is then advected, or transported, over into the Plains, resulting in heavy precipitation.
The third and final phenomenon is, of course, snow-melt; this bomb cyclone developed right as that part of the country was beginning to warm up following a period of very cold and snowy conditions. As such, when more precipitation moved in and temperatures continued to warm, the already saturated surface was introduced to even more water, leading to an increased stress on it and the rivers all along the northern and central Plains.
Source: The Atlantic/ Shutterstock / Aspects and Angles
As the record-breaking bomb cyclone developed on the lee-side of the Rocky Mountain during the early-to-mid part of March of this year, the low-level jet and its ability to transport moisture into the region, and the subsequent melting of snowpack across the region during a relatively short period of time owing to warmer temperatures during this time of the year, Nebraska in particular experienced severe flooding all across the state. And as the region continues to recover, it is times like these that one can look back and see how weather events, such as these, are not made up of one single entity, but are in fact the products of several ingredients coming together at the right place and time. As the states in the Midwest impacted by the flooding continue to recover, there are many ways to help including donations to the local, regional and national flood relief organizations and the American Red Cross .
To learn more about other high-impact flooding events from around the world, be sure to click here!
© 2019 Meteorologist Gerardo Diaz Jr.
USA Today: https://www.usatoday.com/story/news/nation/2019/03/19/historic-midwest-flooding-nebraska-mike-pence-visit/3209623002/
Flood Relief Efforts: https://www.1011now.com/content/news/HOW-TO-HELP-Nebraska-flood-victims-507197401.html