Turnagain Pass Avalanche Forecast

After a nearly two week dry spell, the mountains finally had a fresh dusting of snow in most areas yesterday. Yesterday was a teaser however with only 2-4″ of very low density snow accumulating. Today, on the other hand, will hopefully be enough of a re-fresh to cover the plethora of old tracks littering the mountainsides. From this morning through tonight the National Weather service is calling for 5-9″ of low density snow. They also have a Winter Weather Advisory is in effect. 

That all said, if the snowfall forecast verifies, along with the increase in wind; ridgetop winds due to pick up to 15-20mph from the North and West. We are sure to see several shallow wind slabs, soft slabs and loose snow avalanches. The new snow from yesterday and today is falling on a very weak surface of both near surface facets and surface hoar. It will not take much wind and new snow to create very touchy wind slabs. Due to the small amounts of new snow, these slab should fairly shallow – up to a foot thick, but prevalent. 

What to watch for and keep in mind for today:

1. How much new snow has fallen? 
2. How is the new snow bonding with the old snow? (quick hand pits are great for assessing the old/new bonding question)
3. Winds? Is the wind blowing snow and loading leeward slopes? (most likely to be seen above the trees and along the ridgelines)
4. On steep slopes even a small wind slab could initiate a fast moving sluff
5. Sluffs in the new snow are likely to be quick and gain momentum 

Surface conditions before the new snow: Surface hoar – this is now buried by 3-4″ of new snow from yesterday, with more today.

Unfortunately, we continue to find weak snow near the ground in the region (faceted snow and depth hoar). This is in a variety of layers all found in the bottom 2 feet of the snowpack. Areas with a thicker pack, such as the core slopes around Turnagain Pass, the weak snow is much stronger. But, just 5 miles down the road the pack is shallower and the weak snow is impressively weaker (as can be seen in the video below). After almost two weeks of quiet weather, these weak layers have become harder and harder to trigger as the pack has mostly adjusted. However, though the probability of triggering a deep slab avalanche is low, the consequences are high – as we have been saying for a while now. Keep that in mind along with sticking with safe travel practices.

The new snow we are getting out of the system over us now is not adding much load (only around .5 to maybe 1″ of water equivalent). However, next week’s warm stormy weather could be enough to re-active these old layers creating large dangerous avalanches. We will see.