Major spring flooding is likely on many area rivers

The current forecast for the peak river level at these individual gauges along their associated rivers. This indicates that parts of the Mississippi, Minnesota, and St Croix are likely to hit major flood stage as the snow melts. It's a similar situat

We have now surpassed the heart of winter and are coming out the other side. The issue will now transition from the bitter Arctic cold, to the melting of every single snowflake that has fallen this winter. The North Central River Forecast Center has issued their spring flood outlook for Minnesota and the surrounding states, and it’s not good news. Deep dense snowpack can be found in many areas of Minnesota, Wisconsin, and the eastern Dakotas and that sets the stage for drastically rising river levels when it finally starts to melt and then runs into area waterways.

The current snowpack looks like this:

The depth of the snowpack as of February 26th. Areas around the Twin Cities and some small pockets of southwest Minnesota generally have the least amount of snow. Much of northeastern Minnesota has by far the most, with more than 2 feet in pockets al

Roughly 90% of the state has at least 6 inches of snow on the ground with roughly half over a foot. Much of the northeastern quarter is closer to 2 feet.

Here is a list of the current observed snowpack for some of the many official climate sites across the area:

  • MSP Airport: 4”
  • Chanhassen: 5”
  • St Cloud: 7”
  • Eau Claire, WI: 7”
  • St Croix Falls, WI: 8”
  • Rochester: 8”
  • U of M St Paul: 9”
  • Willmar: 9”
  • Alexandria : 13”
  • Brainerd: 16”
  • International Falls: 19”
  • Duluth: 22”

But it’s not just the depth of the snow that’s the issue, it’s the density, or how much liquid water is locked away in that snow.

As we know, not all snowstorms are the same. Obviously the amounts change, but so does the composition of the snow. Some of it’s very wet and heavy. Great for making snowballs, but backbreaking work to shovel. That kind of snow has a LOT of water in it. Then you have the dry powdery snow that’s easy to shovel and wonderful to ski in. That has a MUCH lower water content. This is called the snow water equivalent of your snowpack. All of these differences in composition affect our spring flooding because that snow turns into water before it runs into area rivers. It’s that water content that ultimately influences our river levels. So in theory, you could have 2 inches of snow on the ground and actually have more water in that snow than another location that has 8 inches of snow on the ground. It just all comes down to density.

So if the snow to water equivalent is the better indicator of how much liquid is out there that will drain into area rivers, then you look at a map like this...

The amount of liquid water that's currently in our snowpack. The overall amount rises as you go from southwest Minnesota toward the North Shore and the lake effect snowbelts near Superior.

These are the more important numbers. This shows that our snow has anywhere from 2"-8” of water locked away in it. Generally more the further northeast in the state you go. Makes sense since nearly every single flake that has fallen this season is still locked away in the current snowpack because temperatures haven’t been warm enough to melt most of it.  So how does this amount of water compare to average?  

Nearly the entire state of Minnesota and much of Wisconsin have an above average amount of water locked away in the snowpack. For the dark blue shaded zones, it's in the 90th percentile.

Every single area that’s shaded in blue in the above map has a liquid water amount that is above the 50th percent, or above the average. In some cases, there are areas above the 90th percentile. Those spots have nearly record breaking amounts of water locked away in the snow for this point in the year. That’s not good if you’re looking to mitigate flooding.

Now, the ground is obviously still frozen so much of this becomes runoff until the snow melts and the ground thaws. BUT, there is another factor that is complicating our flood forecast; soil moisture. While frozen soil is impermeable, once it thaws as the last of the snow melts, it can start absorbing water. But the current soil is VERY saturated. Wet soil cannot absorb nearly as much water as dry soil.  The current soil moisture across much of the Upper Midwest is in the 95th to 99th percentile. This means that the soil is nearly as wet as it has ever been since record keeping began roughly 150 years ago. It also means that our soil will really struggle to absorb any additional moisture. So any additional snow or rain that falls in the month of March will likely become extra runoff whether the ground has thawed or not. That means more water will be entering our waterways and potentially exacerbating an already bad situation.

This is the ranking for the amount of water locked away in the soil across the country. The large green shaded areas indicate much of the Lower 48 has an above average amount of moisture. For the Upper Midwest and much of Minnesota, we are in the 99t

While the situation looks dire for the moment, it can certainly change. The weather we see over the next few weeks will have HUGE implications on the current look at spring flooding. Mild days and chilly nights can lead to a very slow melt and potentially mitigate some of the flooding that’s expected. That said, the opposite can happen as well. A string of very warm days and/or a large storm bringing more moisture to the area could have disastrous consequences.

Is there anything that can be done? Well, not really. If you live in a flood prone area and don’t have flood insurance, consider getting some as soon as possible because it takes 30 days for any benefits to kick in. Outside of that, it’s just a wait and see game and react if and when the time comes.