Turnagain Pass Avalanche Forecast

Skies may be mostly clear, but the winds are howling along the ridgelines. Beginning yesterday, sustained Easterly winds in the 20-40mph range are impacting the mountains. There were no known avalanches yesterday. However, there was a report of a crown and large avalanche in the Center Divide area near Johnson Pass. It is unknown when this avalanche released and we hope to get better eyes on it today. It does appear to have been a large slab breaking near the ground. 

For today, wind slabs will be the primary concern. Watch for these not only in the upper elevations, but in the lower elevations as well. Terrain channeling may be occurring which can load slopes below treeline. In the Alpine, the main concern will be both wind slabs and deep persistent slabs (more on the deep slabs below). Today is a day to watch for wind loading patterns and feeling for stiffer snow over softer snow. Watch for cracks that shoot from your feet. All these signs point to touchy wind slabs. We could see some cornice falls and wind slabs release naturally; if this is the case, these may be able to trigger a deeper avalanche at the upper elevations. 

Strong Easterly winds blowing snow on Seattle Ridge yesterday afternoon.

As mentioned above, at elevations above 3,000′ weak snow sits below a very hard and dense slab. Many of you have likely heard about the large avalanche that was remotely triggered by 2 skiers on the lower benchs of Pastoral Peak on Wednesday. This is unfortunately prime eveidence that the deep persistent slab problem is out there and looming on other upper elevation slopes. We were able to do an avalanche investigation yesterday, see that HERE. This is a low probability, high consequence avalanche issue. It is a tough situation as this problem does not tend to go away quickly. Additionally, these types of avalanches are hard to trigger, thus can lull us into a sense of complacency when days pass with no incidents. Here are some points to consider as we move forward:

–    This danger is on the upper elevations slopes, above 3,000′.

–    No RED FLAGS may be present before an avalanche releases.

–    Several tracks may be on a slope before someone finds the trigger point and releases the slope.

–    The ‘slab’ above the weak snow sitting on the ground is 3,4,5+ feet thick, this means it is difficult to trigger.

–    Because there is variability in the slab thickness, there are places the slab is only 1-2′ thick, or less. These areas are where a person/group of people’s weight can penetrate to the weak layer and trigger a collapse that can then trigger a large avalanche (this is what happend on Pastoral Wednesday).

As this problem persists, steering clear of slopes over 30 degress at the upper elevations, along with runout zones, will be a safer way to enjoy the backcountry.

Photo below of the Pastoral avalanche on Wed, Dec 20th (photo taken on Dec 21st). The route of the skiers is marked on the photo. This is a good reminder that our snowpack ‘set up’ above 3,000′ requires another look at our ‘safe spots’. These large avalanches can send debris where we have not seen debris for 10 years. 

Photo looking down toward Taylor Pass from Pastoral debris.

A look into the snowpack near the point the Pastoral avalanche was triggered.