Perfect Corn
Wednesday, March 24, 2010
By Lisa Van Sciver
Jackson Hole, Wyo.-There is a short window for skiing perfect corn snow. As the supportable crust on the snow’s surface begins to melt, it changes from firm and icy to soft and almost velvety. The sun’s intensity, slope angle, aspect, and temperature factor into the time available for making hero turns on the momentary smooth and forgiving corn snow. When the hour is over, the perfect surface melts and turns to heavy, loose snow.
Daily melting and nightly freezing is the process called melt-freeze metamorphism, which creates clusters of grains near the snowpack’s surface and an early morning crust. During the warm days, the snowpack heats up and the bonds between snow crystals change to water. Once the snow becomes very wet, a moderate amount of water can be hand-squeezed from it. More than very wet is slushy, which is a snowpack with 15-percent or more water content. The particles of slushy snow are no longer bonded, and instead surrounded by water.
A wet snowpack’s buried weak layers lose strength as the bonds between grains turn to water, overall decreasing the snow’s cohesion and increasing the potential of wet slides. Lack of cohesion allows for loose snow slides, as particles no longer hold enough static friction to stay on the slope angle. Wet snow can move on angles as low as 15 degrees.
Noticing wet slides can be tricky, since the snowpack can rapidly change from very stable to very unstable. So while chasing corn, keep an eye on the clock, because timing is everything. JHW
PERMALINK:
Perfect Corn | Planet JH News Article: Snow Report Column
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