Turnagain Pass

This morning will be the final push of warm and rainy weather before skies clear and a cold Northwest wind sets in to freeze the wet and saturated snow. Up to 2-3″ of new snow could fall above 1,000′. This dramatic change in the weather pattern is expected around noon today and by late this afternoon, strong winds along with sunny skies are forecast. The cooling trend will stabilize the lower elevations quickly. At the higher elevations, the winds will search out any remaining soft snow, along with any new snow, and attempt to build wind slabs and grow cornices. Wind slabs could be touchy and may release naturally, yet they should be on the smaller side – up to a foot thick. Wind slabs may also overload weak layers deeper in the pack, contributing to a much larger slide.

This larger avalanche issue is our deep persistent slab problem, which boils down to: triggering a large destructive avalanche 2-4+ feet thick is still possible. For the first time in over a week, there were no new slab avalanches reported yesterday. The last avalanche was a snowmachiner triggered slab in Main Bowl of Seattle Ridge on Saturday. This slope had tracks on it from the day before and was triggered from a flatter area below (remotely triggered from below). To recap, over the past week many large human triggered avalanches and/or natural avalanches have released from Girdwood to Lost Lake (please see Heather’s video if you have not already). Some of these avalanches have been remotely triggered and some with skier/snowmachiners on the slope. Most of these avalanches have occurred below 3000’, releasing on weak faceted snow on a slick crust, 2-4 feet below the surface. A lot of uncertainty remains in the Alpine where slab depths are much deeper and triggering an avalanche could be more stubborn. Widespread buried surface hoar and facets have been well documented at all elevations. 

*With a deep slab problem it is important to remember no signs of instability may be present before a slope releases. It may be the 10th person onto the slope that finds the trigger point and slopes may be triggered remotely. It is crucial to visualize the consequences if the slope does slide. Are there terrain traps below?  Bigger slope = Bigger avalanche. Thin spots near rocks and along ridgelines are likely areas to find the trigger point. 

Main Bowl avalanche from Saturday, March 17th, East aspect. This was a remote snowmachine trigger from below. No one was caught. Photos: Brian Bird

Until the skies clear and temperatures cool down later today, wet loose and wet slab avalanches remain likely. The exception will be Southerly slopes that see sunshine and are out of the winds. These slopes may continue to see wet avalanche activity through the day. A wet point release could be small to large and has the potential to trigger a much larger, more dangerous slab. Pay attention to the surface conditions and avoid slopes with saturated wet snow. 

Cornices are large and looming. Give these an extra wide berth and limit exposure underneath them. Winds today may find enough snow to add to their size and this along with sun later today, may be enough to cause some of break off naturally. A cornice fall could trigger and propagate an avalanche on a slope below.