Upside down

Wednesday, February 10, 2010

By Lisa Van Sciver

Jackson Hole, Wyo.-When standing upside-down, your body wants to fall over, because all your weight is above you instead of below you. To an even greater extreme, imagine if your upper body was half the density of your lower body. If that were to occur, it would be even more difficult to stand upside-down.

Last week’s storm produced upside-down qualities. An ideal storm will arrive warm and leave cold; starting with high density, moist snow and ending with light density, dry snow. A less than ideal storm will arrive cold and end warm, leaving heavier snow on lighter snow. The storm from Feb. 11 to 13 began with light winds and about .2 inches of water and then ended with high winds, gusts above 50 miles per hour, and .5 inches of water. This storm cycle created densely, compacted snow over light, fluffy snow, creating a slab upon a hollow feeling layer. This density and hardness change on the snowpack’s surface resulted in many easily released soft slabs up to 24 inches in depth.

In many areas the existing snowpack also has these upside-down qualities. January and February snowfall has formed into slabs, which lie upon poorly bonded, early season faceted snow. Added loads from recent storms weighted this upside-down snowpack and increased the stress, creating the possibility for an avalanche to release full depth to the ground.

 So drop your probe into the snow and see where it stops. Then push it again, maybe finding less resistance, an upside-down snow structure. This weak structure of well bonded snow over poorly bonded snow is the recipe for an avalanche, minus the trigger. As for new snow, we will take it anyway it falls, right-side-up or upside-down.


PERMALINK:
Upside down | Planet JH News Article: Snow Report Column

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