Turnagain Pass

Due to periods of heavy snow, rain and strong winds, yesterday was the most active day for avalanches yet in this series of storms. A majority of the avalanche terrain that was visible below 2500′ had avalanched. Much of the activity observed was wet avalanches at lower elevations. It was hard to get a good look into the Alpine. For today it is important to remember that conditions remain touchy and travel in avalanche terrain is not recommended. Avalanches may also step down into weak older layers in the pack, creating an even larger slide.

WIND SLABS and CORNICES:
Strong winds yesterday combined with heavy snow will have created large wind slabs and cornices on leeward slopes. With temperatures rising to above freezing in the Alpine these may release naturally and could entrain enough snow to run quite far. Any additional wind today will also add stress.

STORM SLAB AVALANCHES:
In areas out of the wind, expect the recent storm snow to still be reactive. Human triggered slab avalanches 2-4′ thick are very likely.  

How much load is on the old weak surface from March? Storm totals (March 27 – 6am April 5th):

Turnagain Pass:     4″ of H2O, 45+” of snow at upper elevations
Girdwood Valley:    5″ of H2O,  55+” of snow at upper elevations
Summit Lake:         1.5″ of H2O,  15+” of snow at upper elevations   

 AKRR/DOT Avalanche Hazard Reduction triggered slide in the Centerline path on the Seward Highway yesterday. 

Avalanche on Seattle Ridge across from the Sunburst parking lot.

Yesterday periods of heavy rain, rising temperatures and strong winds initiated a widespread wet avalanche cycle below 2500′. The rain/snow line climbed to approximately 1,500′, possibly higher in places.  Many slopes across the advisory area had piles of wet debris at the bottom. Artillery triggered slabs caused long running slides that gouged into wet snow and weak deeper layers in the snowpack. Slopes that did not slide may still today as temperatures climb above freezing in the Alpine and dry snow at upper elevations becomes wet. Additional rain to 2300′ will also add load and contribute to instability. In the event that the sun makes an appearance wet activity may also be exacerbated by more heat.

Avalanches along Seattle Ridge towards the uptrack.

The balance was finally tipped and avalanches yesterday were observed stepping down into old weak layers. Dirty debris in places indicted that some avalanches were running to the ground. Prior to this storm cycle the snowpack consisted of many weak layers of facets and buried surface hoar. We may continue to see avalanches today breaking in the mid-pack or near the ground, with crown depths over 6′ and running the entire length of a slide path.  

Multiple layers of buried surface hoar and facets exist within the snowpack. These layers are overloaded and avalanches are breaking into them.