Turnagain Pass

There was a natural avalanche cycle observed in Summit Lake yesterday as strong northwest winds overloaded the weak snowpack. Avalanches were observed in motion from the highway. There was also a skier triggered wind slab avalanche on Raggedtop Mountain in Girdwood. The skier was briefly caught and carried but skied out of the slide. Thanks to the reporting party for their discussion of the decision making of the day and big thanks to all that sent in observations yesterday.

Natural avalanche in motion observed above Summit Lake on an east facing slope, west side of the highway at 6:42 pm last night. Observer noted that it looked like it stepped down older snow. 3.10.20. Photo: Matt Yoder. 

Skier triggered wind slab on southwest aspect of Ragged at 3000′. Observer noted that it was generally a thin slab but propagated around 300′ across. 3.10.20. Photo: Peter Wadsworth.

The northwest outflow winds were moving snow yesterday and obvious flagging was observed around the forecast area and south to Seward. The AKRR MP 43 weather station that sits near Bench Peak, above and to the west of Grandview, seems to capture these winds. Steady winds in the 20s with gusts into the 50s were recorded in the late afternoon and overnight. Today the winds are forecast to slowly decrease but may bump back up overnight. Turnagain Pass is often spared by this wind direction but where ever you decide to go, it will be important to pay attention blowing snow and surface conditions. There may also be older wind slabs that formed over the past several days. In general wind slabs you find today could be 1-2′ thick and will most likely be found in Alpine terrain on loaded slopes just off ridges and in cross loaded gully features.  Fresh wind slabs that just formed could be tender but older ones may still be reactive and really be best described as a persistent slab due to the Leap day layer of buried surface hoar/small facets.  Observers noted this layer in snow pits dug in Girdwood Valley and in Turnagain Pass. On southerly aspects in some locations this buried surface hoar is on melt-freeze crust. This could well be the weak layer/bed surface in the skier triggered Raggedtop avalanche due to the nature of the propagation and the aspect. Buried surface hoar can be tricky in that it may or may not be widespread across terrain. This is still something we are trying to get a gather data on as we move into the spring break week. If you are heading out today pay attention to terrain features that look loaded or pillowed, watch for cracking or collapsing, and terrain with hard snow over a softer layer.

Wind loading yesterday near Carter Lake. 3.10.20. Photo: Alex McLain 

Leap day buried surface hoar found at in a snow pit at 2750′ in Girdwood valley down almost 2′ that propagated in an extended column test.

Cornices:  Avoid travel on cornices and limit exposure underneath them.

Loose snow avalanches:  In areas that were protected from the wind, sluffs are possible in steep terrain.

Sun effect: Even with cold temperatures the sun may impact surface snow on steep solar aspects.  Be aware of moist surface snow, small roller balls or loose snow avalanches in wind protected spots, especially below steeper rocky areas.