Minnesota loses roughly half our snow depth in just 4 days

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What a difference a few days can make. As we approach the first day of spring, the melt is on as warmer temperatures and rain have inundated much of the state. 

More than an inch of rain has fallen this week in the Twin Cities metro and many parts of central and southern Minnesota. Combined that with temperatures climbing above freezing for more than 60 straight hours and our snowpack has taken a big hit.

The metro has gone from a 19-inch snow depth on Sunday, to just 4 inches late Thursday. 

It’s similar in many areas of eastern Minnesota. St. Cloud has gone from 21 inches to a 10-inch snow depth.  Rochester has gone from 16 inches to 6. The change isn’t quite as dramatic across the north and west though with both Duluth and International Falls dropping from 24 inches to start the week, to 18 inches on Thursday. 

Most of western Minnesota only lost a few inches as well because temperatures weren’t nearly as warm.

With the drastic loss in snow depth, flooding is at the top of many minds, but it hasn’t started quite yet in much of Minnesota like it has in areas just to our south. This is because, while our overall snow depth is down drastically, much of the liquid water in that snow remains in place. This is called compaction.

When snow melts, it melts from the top down. When the top layer turns to liquid, it doesn’t roll off the snow like water rolls down a hill. It actually falls into whatever snow is underneath it and gets soaked into the older snowpack like a sponge. That’s because the snow has to actually have a certain density to it before running off. 

Snowflakes have a much lower density than rain drops, that’s why they fly through the air and change course depending on wind direction and speed. Rain doesn’t fly, it falls because the density is so much higher. It’s this high density that has to be reached by the melting snow before it begins releasing water and running off. Snow first compacts onto itself when melting, then when it hits a certain density point, it begins to runoff.

Now because of this, much of our water is still left in the current snowpack and the density of that snowpack is nearing the release point in many spots. This means that mild days will now release a lot more water than the 40s have over the last couple of days. This will likely lead to our highly anticipated spring flood in the coming days and weeks.