Wintry mix spreads across Minnesota

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Yes, it’s been a cold and snowy March. Yes, it seems like winter is dragging on forever this year. But our reluctant spring has a silver lining. 

The frequent freeze-thaw cycles mean the 2 to 7 inches of water that were trapped in the snow cover are releasing more slowly into area rivers, and that may be slightly easing our significant flood risk this spring. 

This March in Minnesota has featured nearly continuous freeze-thaw cycles. You can see on the graphic at the top of this post how almost every day has recorded daily temperatures cycling above and below freezing in the Twin Cities.

We’ve avoided rapid temperature rises into the 50s, 60s, or even 70s that often occur in March. That’s a good thing when it comes to melting the snow cover nice and slowly. A slower melt means a slower runoff profile into our rivers, which can help mitigate flood risk. 

You can clearly see the effect on the daily 

 in the Twin Cities west metro over the past week. See how water levels rise and then fall each day as the temperature changes?  

The higher rise on the chart is driven by rainfall on March 21 and 22. 

You can also see the water temperature reflects the 

 — the temperature difference between the minimum at night (low) and the maximum during the day (high) — over the past week. See how they rise during the day with the air temperature, then fall to around 32 degrees at night as the air temperature falls below freezing? 

So our constant freeze-thaw cycles slow down the runoff rate as the snow melts more gradually into our river systems. If we had a big warmup and more rainfall, you would see huge and prolonged runoff spikes as snowmelt rapidly rushes into the rivers. 

National Oceanic and Atmospheric Administration’s latest overall flood risk

 is still much higher than average in our region. The latest flood report updated Monday reflects current and forecast weather conditions. 

NOAA hydrologists are also seeing the potential benefits of our slower runoff profile in area rivers. But the risk of major flooding still lurks, especially if we get a quick warmup with additional rainfall. 

The threat of moderate to major flooding remains high on some area rivers.

 in the snow cover across Minnesota and Wisconsin. 

Snow cover in our region is still in the 90th percentile historically for this date. 

Here’s the latest outlook for the Mississippi River at St. Paul.

And here’s the outlook for the St. Croix River at Stillwater. 

The overall weather pattern still favors cooler and wetter than average weather over the next two weeks. 

So while we’re not out of the woods yet on flood risk, our reluctantly cool spring has been a benefit.

Weather and Climate News

Updraft® - Minnesota Weather News

Paul Huttner

Author

The frequent freeze-thaw cycles mean the 2 to 7 inches of water that were trapped in the snow cover are releasing more slowly into area rivers, and that may be slightly easing our significant flood risk this spring. 


Flood watch silver lining: Slow thaw easing snow melt runoff, so far

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