Since March 1, we have had 5-9 feet of snow and 5-9 inches of snow water equivalent (SWE) throughout the Central Wasatch. This has been a great test of our buried persistent weak layers (PWL). Prior to the start of this stormy March we had a layer of very heavy snow (almost rain) that fell with an associated dirt layer on March 2. This melt-freeze layer was buried and in turn faceted, causing a seven-to-ten day avalanche cycle. Recently, we have had extended column tests showing that while the layer is still reactive, it is becoming harder to initiate propagation. The last avalanches associated with this dirt crust were on March 7 in Days Fork (Crystal Palace) and Upper Catchers Mitt on East Kessler.

The last reported avalanches on this layer of facets near the ground were in Depth Hoar Bowl on February 21 and an avalanche in the Bountiful Session’s area on February 22.

There is a small possibility that someone could trigger an avalanche on this early-season faceted layer in a thinner, shallow snowpack failing 2-5 feet deep. This is more likely to be the case in steep, rocky, greater than 35°degree terrain. Any slope with these features that is not supported, such as a hanging snowfield, is a likely place to trigger an avalanche failing on this layer of faceted snow near the ground.  

Based on the information we have gathered, the chance of triggering an avalanche on this layer falls into the LOW category, “ small avalanches in isolated areas or extreme terrain”. Removing the persistent weak layer (PWL) does not account for the human factor and going after steep exposed lines that may have a thinner snowpack puts backcountry travelers at a higher risk of triggering an avalanche on this layer.

This problem is being relegated to dormancy right now, though there is always the chance that with warming temperatures this spring and periods when we stop freezing (going below 32°F) for longer than 24 hours that melt-water hitting the weak snow near the ground could initiate a large natural spring avalanche cycle, but this isn’t the case right now, and the snowpack could always melt before it avalanches. Dormancy refers to the layer being present but not being active.

Low Danger does not mean no danger, and you can’t trust a facet till it’s melted.

Photo below showing three different snowpacks all dug around the end of February and beginning of March on north facing slopes. The photos on the lookers left and center show deep snowpacks, over 6 feet deep. The right side shows a thin faceted snowpack that had previously avalanched and is 3 feet deep and in a repeater avalanche path.

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