Turnagain Pass Avalanche Forecast

Last night we got reports of an avalanche on Repeat Offender, the site of the large fatal avalanche in 1999.  A group of snowmachiners had just started descending the standard trail from Seattle ridge when it released remotely 100 yards away.  Initial reports estimate the size as 600-1200 feet wide.  It undoubtedly took the entire depth of the snowpack, breaking on old October and November weak layers.  Reports say that Main Bowl also slid on the west side of the ridge.

The deep slab problem is difficult to understand because it won’t show signs of instability until it avalanches in a big way.  You also won’t see a lot of slopes avalanching on the same day, meaning that the mountains will look good and enticing.  The problem is that when you find a trigger point, the resulting slide will be much bigger than you want.  This is a low frequency, but very high consequence problem that is difficult to predict.

We have compiled ample evidence to show that the mountains are ripe for this to happen again.  Over 10 feet of new snow in the last 2 weeks has already brought down a number of large avalanches including at Tincan, Seattle ridge, Johnson Pass, Portage, and elsewhere.  This is the most dangerous persistent deep slab problem we’ve had in our region in a number of years.  The only way to avoid becoming a statistic is to alter our behavior and choose conservative, lower angle terrain.

Yesterday we found a small reactive wind slab in the top 6 inches of surface snow at treeline.  Wind deposit areas may have this layer of stiffer, less stable snow.  Compared to the deep slab issue, this is a relatively minor and manageable problem.