Turnagain Pass

Just as the unwritten rule states, after three consecutive warm nights in the mountains with no re-freeze at the ridgetop elevations, wet avalanches start running. Yesterday was the first of these days and in fact, several wet loose and shallow wet slab avalanches ran naturally. These occurred on all aspects, with North and West aspects seeing the majority of the activity at Turnagain Pass. What about today and tomorrow? Although stormy weather with slightly cooler temperatures have moved in, we can expect similar wet avalanche activity. 

This morning wet snow is falling above 2,000-2,500′ and rain below this. Only a few inches of snow is expected and this should stick well to the wet and warm old surface. That said, winds are blowing in the 20’s mph along ridgetops, which is enough to move the new snow into shallow wind slabs at the higher elevations where the snow is drier, such as 4,000′. Most of our terrain however is lower and wet snow issues will remain the main concern. 

WET SLAB, WET LOOSE and CORNICE FALLS:
As the snowpack continues to loose its strength with the springtime melt-down, several different wet avalanche concerns are present. Things to keep in mind if you are headed out: 

1. Is the snowpack frozen or wet and soggy? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
2. Are you punching through a shallow crust into wet soggy snow? A shallow re-freeze is still weak and could avalanche.
3. Are you seeing recent avalanches?
   
4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
5. Buried weak layers in the pack can make a small avalanche or sluff larger by propagating across the slope and/or stepping down.
6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

Wet loose and wet slab avalanches on the West face of Magnum, occurring Monday, April 24th

Wet loose avalanches in the North chutes of Tincan

Wet loose avalanches in the North chutes of Cornbiscuit

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Similar to the wet issues above, glide avalanches are also occurring with the springtime melt-down. Glide cracks are opening up and releasing on many slopes in the region – steer clear of any slopes harboring glide cracks. Check out the photo below from the motorized up-track. This slope is notorious for producing glide avalanches. Additional glide avalanche activity is expected today and through the week.
 

Photo below: A comparison of the glide avalanches on Seattle Ridge during the past couple days (top photo from Saturday, April 22nd, bottom photo from yesterday, April 24th). The glide that released yesterday sent debris over a portion of the Turnagain Pass motorized up-track. 

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Upper elevation Northerly aspects have now warmed to the degree the surface layer is wet and saturated. How deep the wet snow exists varies, but what this warming does is weaken the snowpack and increases the stress on underlying weak layers. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the upper elevation North, West and Easterly snowpack warms up, these weak layers could re-activate and large natural slabs are possible along with the increased chance for a person to trigger a slab.