Spring flood risk rises to 'well above average' after heavy snow season

It’s snowing again. That persistent theme this winter has added up to boost flood risk across the Upper Midwest.

Thursday’s updated spring flood outlook from the National Oceanic and Atmospheric Administration’s North Central River Forecast Center has boosted the flood risk even higher for the Upper Midwest.

Hydrologists now estimate a 61 percent chance of “major” flooding this spring on the Mississippi River at St. Paul. The chance of major flooding for the St. Croix River at Stillwater has been boosted to 73 percent. That’s compared to an average chance of just 11 percent in any given year.

Snow water equivalent levels elevated

There’s a lot of still frozen and liquid water equivalent sitting in that snowpack across our region.

NOAA’s latest snow water equivalent map (above) shows a range of between 2 to 7 inches of water equivalent in snow cover across Minnesota and western Wisconsin. That’s like a 2 to 7-inch rain event just sitting there on the ground waiting to be activated into runoff this spring.

Snow water equivalent levels this spring rank in the top 90 percent of the past 70 years across the Upper Midwest. Only 5 to 10 years have seen this much SWE on the ground in March in the past 70 years.

Flood risk rises

Here are the updated flood risk estimates for some select rivers around our region based on Thursday’s updated flood outlook.

Mississippi River at St. Paul

• Now seeing at least a 50 percent chance of reaching major flood stage

• Minor: 91 percent vs. 25 percent normal

• Moderate: 81 percent vs. 19 percent normal

• Major: 61 percent vs. 12 percent normal

Mississippi River at Red Wing

• More than a 50 percent chance of reaching major flood stage

• Minor: 93 percent vs. 19 percent normal

• Moderate: 83 percent vs. 14 percent normal

• Major: 67 percent vs. 10 percent normal

St. Croix River at Stillwater

• The probability of seeing major flood stage now tops 70 percent

• Minor: greater than 95 percent vs. 24 percent normal

• Moderate: 91 percent vs. 19 percent normal

• Major: 73 percent vs. 11 percent normal

Minnesota River at Montevideo

• Minor to moderate flood stages becoming more likely, while chances of reaching major flood stage are closer to normal

• Minor: 93 percent vs. 30 percent normal

• Moderate: 50 percent vs. 21 percent normal

• Major: 16 percent vs. 11 percent normal

Spring weather outlook

Weather patterns over the next 60 days will now determine how quickly the snow melts, and if major flooding occurs.

A cooler-than-average, long, slow melt season with below-average precipitation is the best scenario for minimizing flood risk. But if we warm up quickly and add heavy rainfall and thunderstorms, a gush of snowmelt runoff will send many rivers quickly into flood stage.

NOAA’s overall temperature outlook for the rest of March favors cooler-than-average temperatures.

NOAA’s precipitation outlook favors near to above-average precipitation across the Upper Midwest through May.

Thursday’s updated spring flood outlook suggests people near vulnerable flood zones should prepare for the possibility of moderate to major flooding this spring.

Stay tuned.