Turnagain Pass

During the springtime warm-up and the snowpack melt-down (or shed cycle), there is an ‘old-timer’ rule of thumb. This goes as follows: One can start expecting wet avalanches to begin after three consecutive nights with no re-freeze along the ridgetops. Last night was the second night without a sold re-freeze, and tonight will be the third….. 

Although many South and Southeast slopes such as Seattle Ridge have already melted down over the past 2 weeks of sunny weather (meaning significant wet avalanche activity has occurred), there are still West, North and East slopes that remain intact. Westerly and Easterly slopes are theoretically next in line. Will we start seeing the West/East aspects release this week – there is a good chance with the cloudy and warm weather forecast. So what to watch for if headed to the mountains? Is the snowpack frozen or is it mushy and wet? That’s the key.

Cloud cover: Starting last Friday night, cloudy skies have been trapping in the daytime heat and severely limiting the amount of overnight re-freeze. Although the breezy winds have helped combat this, the pack is still loosening up and becoming weaker. This trend is expected to continue with the forecasted warm, cloudy conditions. Aside from the avalanche concern – many folks have been traveling on glaciated terrain – snow bridges over crevasses are sagging and punching through is becoming more likely.

WET SLAB, WET LOOSE, GLIDE AVALANCHES and CORNICE FALLS:

These are the different characters of avalanches that occur with the melt-down or shed cycle during springtime. Things to keep in mind if headed out:

1. Did the snowpack re-freeze overnight in your location? A hard frozen snowpack is stable, a soft mushy snowpack is dangerous.
2. Are you punching through a shallow crust into wet soggy snow as in the photo below? Also a sign the snowpack is weak and could avalanche.
3. Do you see any recent avalanches.
4. Are you in a runout zone? Can an avalanche releasing above wash debris over your location? Avalanches can run into valley bottoms.
5. Buried weak layers in the pack can make a small avalanche or sluff become bigger by propagating across the slope and/or stepping down.
6. Wet avalanches are hard to escape if you get caught. A small slide can be deadly if it pushes you into a terrain trap.

Yesterday, this was the only recent avalanche noted – a small glide on the lower South face of Tincan 

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Glide avalanches are still releaseing here and there – we saw one yesterday pictured above. Watch for glide cracks and avoid being under them as they can release at any time.

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Upper elevation Northerly aspects warmed yesterday enough to moisten the top 4″ at 3,800′. This trend is expected to continue with the forecast warm, cloudy conditions. With the added warmth of the pack in these shaded zones, increased stress on underlying weak layers will be occurring. There are several buried persistent weak layers in the snowpack; ranging from buried surface hoar 2-6′ deep, mid-pack facets and facets near the ground. Shallow snowpack zones such as the Summit Lake area harbor depth hoar near the ground. As the snowpack warms up, these weak layers could re-activate and triggering a slab avalanche is possible. This is a low probability, high consequence problem. Keep these points in mind:  

• It will take someone hitting a ‘thin spot’ in the slab, or a large trigger such as a snowmachine and/or groups of people or a cornice fall
• There may be no signs of instability before the slope breaks
• Several tracks may be on a slope before it releases
• Stability tests may not produce any notable results