Frost Depth in Minnesota for Winter 2018

Frost depth varies across the state in January 2018, but is generally deeper than it was last two years.

The map on the right depicts the depth that the ground is frozen under sod across the state. The frost depth is measured by a simple instrument called a frost tube. The liquid freezes in the tube as the ground becomes colder. Frost tubes were installed by the National Weather Service and the US Army Corps of Engineers (USACOE) at various places around the region. Frost depth readings are updated by the USACOE on a weekly basis.

There are also temperature sensors that can be placed in the ground and measure the temperature and this way one can approximate the depth of the frost. The North Dakota Agricultural Weather Network (NDAWN) has sensors along the border with Minnesota. This information can be seen here

Snow can insulate the ground from the air above it and studies have shown that about four inches of fluffy snow will form an effective layer of insulation. When there is a deep snow pack, there can be little to no frost in the ground. Where the landscape is free of snow, the frost can penetrate much deeper.

Below is a history of Frost Depth Information from a volunteer site in Maplewood, MN just north of St. Paul.

Frost under sod at Maplewood MN 55109

Year      Frost In Frost Out Deepest frost
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2000-2001 Nov 22  April 4   29.3 inches
2001-2002 Dec 21  April 12  17.0 inches
2002-2003 Nov 13  April 11  32.3 inches 
2003-2004 Dec 2   March 28  29.3 inches
2004-2005 Nov 24  April 10  31.2 inches
2005-2006 Nov 30  April 2   19.5 inches
2006-2007 Nov 29  April 9   30.0 inches
2007-2008 Nov 23  April 18  35.2 inches
2008-2009 Nov 10  April 7   33.8 inches
2009-2010 Dec 4   March 16  10.0 inches
2010-2011 Nov 23  April 2    5.0 inches
2011-2012 Dec 1   March 16  26.0 inches 
2012-2013 Nov 24  April 18  32.5 inches*     thawed from Early Dec to Dec 24
2013-2014 Nov 23  April 12  19.3 inches
2014-2015 Nov 28  April 4   30.5 inches
2015-2016 Dec 19  March 9    9.5 inches (shortest duration)
2016-2017 Dec  8  March 29  16.0 inches 
2017-2018 Dec 19            17.5 inches (as of March 5, 2018)   
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Median   Nov 23  April 8   26.5 inches  2000-2001 to 2014-15