Snow bales in Gladstone, Illinois
by Paula Johnson
This latest blizzard has produced hazards, closings, crazies and a rare phenomenon. My cousin Sue who lives in Monmouth, Illinois, got a photo from a friend of hers, Lindsey, who lives on a farm near Gladstone in West Central Illinois.
Lindsey awoke to find snow bales in her fields. These balls of snow are a winter rarity. For snow bales or snow runners, snow donuts, snownuts or wind snowballs to form, conditions must be ideal:
• A thin surface layer of wet, loose snow must be present and have the temperature near the melting point of ice (about 3-5 degrees above freezing);
• Under this thin layer of wet snow must be a foundation of some substance to which the wet snow cannot stick, like ice or powder snow;
• The wind must be strong enough to move (roll) the formed snow rollers, but not so strong to blow them apart;
And, if that isn’t enough…
• Gravity must be enough to allow the snowball to roll.
With gravity, we get snow rollers!
This last one is why some hilly areas are more common for this phenomenon to occur than pure flat land. However, the terrain cannot be too hilly or the snow bale will develop traction and roll apart if it goes too fast, too far.
Mountainous regions have too steep an incline which lends itself to avalanches rather than snow bales. Some inland areas of the northwest such as Idaho or Washington are possibilities, yet the Midwest is the most common region.
Because the snow bales are usually started with chunks of snow or ice, the wet snow often forms clumps to begin the process. The snow cannot be too wet or the wind will not be able to roll it along. No ball will form.
A slightly hilly section of prairie will often have harvested fields so the bale as it rolls will pick up dirt or debris to help hold the structure. Thus, the snow must also be not too wet or it will not be able to pick up the debris as it rolls.
An area of the Rocky Mountain National Park, a most unlikely spot for snow bales, had some form that had ridges like the edge of a gear.
The wind must also be steady enough to maintain a consistent roll – about 30 mph. Light breezes won’t cut it, and heavy winds will break it up before it starts.
I call this phenomenon the Goldilocks Winter Phenomenon because everything must be “just right.”