Blase Reardon and Chris Lundy - Going to the Sun highway avalanche forecasters in Glacier National Park in the early 2000s - put forth an excellent model for
forecasting wet slab avalanches in their excellent
2004 ISSW Paper. The structure was key, they said, and it came down to needing three main ingredients:
A Water Factory (ie-rapid melting of the snow surface through rain or meltwater via temperatures/solar radiation)
A Cohesive Slab (likely with preferential drainage channels)
The "Funny Business" (ie- more coarse grains ie-facets/depth hoar and or facet/crust combinations).
The Water Factory is in full swing, with significant solar radiation and minimal cloud cover. We're seeing the melt of the two most recent storms (the upper snowpack). Let's look at the
Mid-Mtn temperatures (7450') in Provo. Daytime highs have reached 43, 51 and (as of 3pm on today/Tuesday), 53°F. Take a look at the chart below. You'll notice that there has not been a deep, full refreeze since the morning of the 23rd. This suggests (all things equal) that the water factory has been working overtime since then, providing free water throughout the snowpack. It just depends on the structure and the "plumbing" of the snowpack. Free water pooling in the funny business can lead to wet slab avalanching. Sometimes the water is able to flow unimpeded all the way to the ground level. On steep quartzite slabs, this may produce glide slab avalanches. In other areas, the water may flow out into natural water courses, following gravity. You can often see water running down the state roads of BCC and LCC in the spring and this can be a good sign of good plumbing.
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A Cohesive Slab exists as the settled snow for the month of March and we'll say, 1-4 feet thick, give or take. The slab is made up of rounded grains that will eventually become isothermal and eventually transition to melt-freeze grains.
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The Funny Business might be made up of the facet/crust/dust layering 1-3 feet down. It may also be faceted snow still lingering in repeater avalanche paths.
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Time will tell.
