With the active, very snowy pattern the past five weeks, the question of “what is spring flooding looking like?” has come up more and more. The National Weather Service is set to release its first spring flood outlook of the season on Thursday, February 21. An updated outlook is scheduled for Thursday, March 7. There may be additional outlooks depending on conditions.
The Turkey River in parts of Clayton County rose 12 feet overnight due to flash flooding and heavy rain. But a lower projected crest should prevent in damage in small towns along the river like Garber.
While the amount of snow is often top-of-mind when it comes to spring flood potential, it’s just one of several things that forecasters look at. In addition to the location of the snowpack and how much water is within it, they also consider:
- Fall precipitation and soil moisture going into winter
- How deep frost is in the ground
- Melting conditions
- Upcoming precipitation trends (odds of it being wetter or drier than normal)
- Streamflow (the amount of water already going through rivers)
- River ice
Soil moisture is running very high because of the wet weather in the fall that lasted into December. That means the soil can’t hold a lot more water. Currently, frost is about one to two feet deep. Streamflow is generally near or a bit above normal; since they’re not running too high, they can deal with some rises. Finally, there is about an inch or two of water in the snowpack right now, with two to four inches in northern Iowa and southern Minnesota where some of our rivers begin.
Thursday’s outlook will detail what the odds of spring flooding are compared to historical averages on rivers throughout the area.