How are river forecasts created?
Predicting how the weather will behave can be challenging – and the same can be said for predicting river flows. Coming up with river forecasts takes collaboration from different groups.
The North Central River Forecast Center (NCRFC) in Chanhassen, Minnesota, leads the process. They run the complex simulations that model how rivers will respond to rainfall. The local National Weather Service (NWS) offices pass along rainfall reports, which the NCRFC puts into their models. Rainfall estimates from radar fill in the gaps, since there aren’t a ton of rainfall observations all over the place. This gets put together with observed river flows, along with soil moisture and the amount of rainfall that’s forecast to fall over the next 24 to 48 hours.
The computer models churn through all that information and make predictions. The forecasters at the NCRFC look those over and make adjustments. Then, they collaborate with the local NWS offices to further refine the forecast based on local experience and perspective. Forecasts for the Mississippi River also involve coordination with the Army Corps of Engineers.
Being able to model how water will move is complicated. It requires an accurate picture not just of how much rain fell, but how the water is (or isn’t) being absorbed into the ground, how it’s moving into ditches and streams, then into the larger rivers. Every acre and every waterway matters! Just like weather forecasts, river forecasts can end up being wrong when the data isn’t good enough or our understanding of how something will react doesn’t quite match up to reality. Local efforts, such as at the Iowa Flood Center, and national efforts, like those at the National Water Center, are working toward improving river level forecasts.
Thanks to Jessica Brooks, the service hydrologist at the Quad Cities NWS, for providing information on the river forecast process.