National Weather Service Weather Forecast Office

 

Parts of the Upper Minnesota and Mississippi River basins now have an above normal risk for river flooding with the spring melt. 

Parts of Southern and Eastern Minnesota as West Central Wisconsin remain at risk for flooding due to Concrete Frost. 

With the additional rain and snow in March, conditions have changed from normal with the early March outlooks to Above Normal Risk for River Flooding with the March Outlooks issued on March 29th for locations including:

• Montevideo on the Minnesota River
• Long Prairie on the Long Prairie River
• St Cloud in the Mississippi River

The following locations have a normal risk for flooding.

• St Cloud on the Sauk River 
• Redwood Falls on the Redwood River 
• Mayer on the South Fork of Crow River 
• New Ulm on the Cottonwood River
• Granite Falls on the Minnesota River
• Savage on the Minnesota River 
• Anoka on the Mississippi River
• Minneapolis on the Mississippi River
• St Paul on the Mississippi River
• Hastings on the Mississippi River
• Lock and Dam 3 on the Mississippi River
• Red Wing on the Mississippi River
• Stillwater on the St Croix River
• Fall Creek on the Eau Claire River - In Wisconsin

While severe to extreme drought conditions still exist still across the region, precipitation from December 2012 through the end of March has been near normal to even above normal in some areas. Hence some regions do have a decent snow pack. Snow depths of 1.5 to over 2 feet are common in the upper Minnesota and Mississippi River Valleys.

Snow Depth on March 25, 2013

In the areas with deeper snowpack, water equivalents (shown below) of 4 to 6 inches are common.

Water in the Snowpack or Snow Water Equivalents  - March 25, 2013

The graphic below shows the "Chance of Exceeding levels during an Entire Period" for Montevideo, MN. The line with black triangles shows the risk for this year. Note: The black line is plotted to the left of the Blue. The blue line is the the historical risk for flooding for April through June while the black line is the risk of flooding for this year based on the amount of water in the snow pack, frozen soil, and soil moisture. Hence as of late March, we have an above normal risk for reaching minor flood stage and a near normal risk for moderate and major flood stages at Montevideo, MN.   

 

Chance of Exceeding levels during an Entire Period - Montevideo, MN

 

For additional locations, reference the NWS Advanced Hydrologic Prediction System website at http://water.weather.gov/ahps2/index.php?wfo=mpx , click on the forecast location and then select the “Chance of Exceeding levels during an Entire Period”.

For a tutorial on how these graphics are generated and how to interpret them, see the YouTube shown below.

  

In addition to the river flood threat, we could see flooding due to ice jams. This is of particular concern in the Upper extent of the Minnesota River valley as well as the Mississippi River upstream of Anoka. Ice jams tend to form near river bends and on bridges. Unfortunately we are not able to predict ice jams and associated flooding would not incorporate in the outlooks described above or in the 7-day river forecast products.

If you see an ice jam, please report this information to the NWS immediately. 

In addition to the river flood threat, this winter parts of Minnesota and Wisconsin has concrete frost. Concrete frost is when the top layer of soil becomes saturated and is solidly frozen. Even though this area has seen days with above freezing high temperatures, overnight lows for the most part have been below freezing. So we still have broad areas of concrete frost. Until it thaws and allows moisture to travel through the soil, any rain/snow melt will run off similar to how it does on concrete and could cause broad overland flooding and quick responses in creeks and streams.

The image below shows the areas of concern for Concrete frost and potential quick response flooding.

 

Concrete Frost - Areas of Concern

The video below provides more information on concrete frost.

  

 

For more information concerning the threat for flooding as well as low water levels through the end of June, reference the   Spring Outlook and Water Resources product at

http://water.weather.gov/ahps/water/textprods/view.php?wfo=mpx&prod=ESF

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