Are tornadoes affected by snow on the ground?

Hi Tom,
Are tornadoes affected by snow on the ground? Has there ever been a tornado touchdown in an area with significant snow cover?
— Robert Pape, Park Ridge

Dear Robert,

We asked National Oceanic and Atmospheric Administration Storm Prediction Center Director Russell Schneider and Greg Carbin, forecast operations branch chief for NOAA Weather Prediction Center. Both said that while the cold, stable air over snow cover would inhibit tornado formation, a weak twister might be possible. In April 2011, a tornado hit near Merrill, Wis., while lakes were frozen, and in January 2008, two hit in Wisconsin along the snowpack’s south edge. While it is common for tornadoes to occur in the warm sector of storms that produce snow on their cold flanks, it would be almost impossible for one to develop in the cold, snowy portion.