Turnagain Pass

We had a report of a couple avalanches in the lower elevations north of the Girdwood Valley yesterday (1100-1900′). These were around a foot deep, 40′ wide and broke in older weak faceted snow. They were not large due to the smaller terrain features they occurred on. No one caught.

We also had a report of a group in the Eddies and Sharks Fin area (north side of Turnagain Pass) who experienced three ‘massive whumpfs’ at the lower elevations (800-1300′). No avalanches triggered.

Much anticipation surrounded last night’s snowfall event and hopes remain for the next system slated for this evening. Unfortunately, there just wasn’t quite enough oomph… It appears only 2-4″ of snow fell overnight, yet there is a small chance another inch or two more could fall before a break in precipitation midday. The next system moves in this evening with a shot for 2-3″ of additional snow tonight. Winds associated with last night’s event were steady in the 15-20mph range from the east and have decreased this morning. Expect the east winds to slowly rise through the day and by sunset be blowing around 20mph.

Wind Slabs:  Avalanche issues will be centered around new wind slabs formed in the new snow. These should be relatively shallow, in the 6-8″ range due to the modest new snow amounts. However, there are some older wind slabs under the new snow that still could be triggered. In this case, a larger slab may release. Furthermore, that funny business of facets and buried surface hoar sitting in the top few feet of the pack could also create a larger avalanche (more on that below in Problem #2).

Things to watch for today:

• New fresh wind slabs from last night (should be easy to identify)
  • Look for recent wind deposited snow, stiff snow over softer snow
  • Watch for cracks that shoot out from you
  • If the winds pick up earlier than expected today, watch for active wind loading and new wind slab formation
• Lingering wind slabs are also a concern. Several of these were triggered the past couple days and may still be reactive.
  • Old slabs may be hidden under the new snow and difficult to identify
  • Quick hand pits are a good way to see if there is an older slab under a couple inches of fluff.

Storm Slabs?:  If you are lucky and find yourself in a zone with over 5″ of new snow, watch for shallow storm slabs. The new snow came in ‘upside down’, with heaver snow over lighter snow. This can allow for the new snow to avalanche as a soft slab with the slab thickness equal to the new snow depth.

Loose Snow Avalanches (Sluffs):  Shallow sluffs in the new snow will be likely today. Watch your sluff on the steeper slopes.

Wet snow sluffs?:  Temperatures warming to above freezing at sea level may create some roller balls and small wet sluffs on steep terrain features below 500′.

We continue to track two weak layers of snow (surface hoar and facets) buried in the top three feet of the snowpack. The data continues to show triggering an avalanche in one of these layers remains possible. The smaller avalanches from yesterday failed in one of these layers as well as the whumpfing reported.

We know these layers are present in most areas and at all the elevation bands. The trick is, they are not reactive everywhere. The new snow and wind-loading could add a little more stress to the snowpack. There may be old hard wind slabs sitting on top of the weak layers allowing you to get well out onto the slope before it fails or failing after other machines or skiers have have already ridden the slope. Triggering a fresh wind slab or cornice fall may step down to one of these buried weak layers. As we have said before, this snowpack has to be viewed with some uncertainty and caution.  We need to keep in mind that these weak layers exist, watch for signs of instability (with the caveat that they may not be present but the slope may be unstable), follow safe travel protocol and evaluate terrain consequences.

Snow pit at 3,600′ in the Johnson Pass area on the south end of Turnagain Pass (pit is from Thursday 2/25). Take home is there are facets in top couple feet of the pack here that are showing reactivity and hence the chance a person could trigger an avalanche 1-2′ deep at this location.