Why is there a high chance of major flooding this year?
By Christopher Ramos
Spring means flowers blooming, warmer temperatures and in our area, the threat of flooding on the Mississippi River. The National Weather Service released a report last week saying that the chances of river levels exceeding major flood stage in the Quad Cities is now at 82%. Matt Wilson, Senior Service Hydrologist at the National Weather Service Quad Cities office, explained how that risk level rose so high.
“Since spring flood outlook number one came out in early February, we have had a very wet February for the upper Mississippi River basin, particularly the Mississippi headwaters up in Minnesota and Wisconsin,” said Wilson. “Some areas up there have gotten 200% to 400% more precipitation in February and early March than they would in a normal year. Currently the snowpack up there is somewhere between 20 and 40 inches of snow, which is carrying four to six inches of snow water equivalent. That’s the water if you took all the snowpack and melted it out, that’s how much water is in the snow. So broadly, we’re seeing four to six inches with many pockets of six to eight and even eight to 10 plus inches in some places. That’s what’s really our big risk factor this year, all of that snow water that’s up north. Eventually it melts, it gets into the streams and it flows down here to our area.”
The speed of the snowmelt is going to determine how bad the flood season will be. Colder temperatures like the area have been seeing lately will slow the melt and allow water to enter the streams and rivers slowly. “The more we get into that mid-April time frame, the more worried I become, because that’s when we typically start to see those 50-60 degree thunderstorm events start to form up there,” said Wilson. “That’s our worst-case scenario, to get a warm rain event on that snowpack. What we want to see is a slow steady melting; basically we want to see above freezing temperatures during the day and then cooling back off at night so that the pack freezes back up. That gives us kind of a pulsing snow melt and that lets that snowpack out easy and gradually over the course of a few weeks instead of rapidly over the course of a few days.”
Wilson urges both residents and city leaders to use this time to prepare, just in case. He says now is the time to check on supplies, line up volunteers, arrange for training, and start cleaning. “One of the big things that we always try to push in the springtime is that after the fall and the winter, it’s time to get into those ditches and culverts and make sure they’re cleaned out so that when we do get some spring rain events, that water has the ability to get into the appropriate drainage systems unfettered.” Unrestricted access to drainage systems isn’t going to impact river flooding, but it will help ease flooding on roads and in ditches.
It’s too early for more of a prediction, which can be frustrating for both local leaders and residents, according to Wilson. “It’s still very much in flux just because it really is going to depend on how quickly that snow melt comes. We’re working with the National Weather Service’s Central Region and the North Central River Forecast Center up in Chanhassen MN. Some of our local weather forecast offices up here are going to be issuing a spring flood outlook update on March 23rd, so we’re hoping that by March 23rd, we’ll have a better handle of what April’s going to look like, at least as far as temperatures and we’ll be able to give a better estimate on what we can really expect. We’ll also have another two weeks of seeing what the snowpack up north is doing, if it’s going to continue to grow or if we’re going to see some melting.”
Even though flooding is expected, the outlook isn’t as bad as it could be, said Wilson. “Most points along the river were over 90% for even moderate flooding, so I would expect that we will see probably at least that. I guess the silver lining is that when we look back at the 2019 spring flood outlook, in 2019 at the Rock Island gage it was a 50/50 shot for 22.6 feet, which was setting a record at the time. This last spring flood outlook, it was only 20 feet, so we’re still multiple feet below 2019 expectations. It could be an above average flood season, but right now we’re not looking at something quite as catastrophic as 2019, so I guess that is kind of a better way to look at it.”
