Turnagain Pass

As of this morning, the storm rages on. Although it is raining below 1,500′, it is snowing and blowing at the upper elevations. Storm totals in these upper elevation areas have been variable: from only a few inches in the Summit Lake area to ~2′ on Turnagain Pass and 4′ or more in the Girdwood and Portage Valleys. These numbers are for ~3,000′ and above and are estimated from the amount of rain/wet snow reported from weather stations at lower elevations (see those water numbers in the Mountain Weather section). Along with the snow, ridgetop winds have been strong and sustained from the East. Considering this, slab depths for avalanche activity are variable, 2-5′ or more.

The primary concern for today and into the remaining part of the week will be how the new snow is bonding with the pre-existing surface. We have been talking a lot about a widespread layer of surface hoar that extended to the ridgetops before being buried under the current storm snow. This set up has the potential for inducing widespread avalanche activity. See video from yesterday. Unfortunately, with little to no visibility there is a good deal of uncertainty as to how the new snow has been acting. Along with this, our field days since the storm began have only allowed us to see what is going on from mid-mountain elevations and below.

All that said, the message is simple: Several feet of new snow combined with wind falling on a weak layer with a slick bed surface below requires a conservative mind set.

Below is the snowpack from a slightly scoured area on the Sunburst ridge yesterday. At 2,700′ the snow changed character significantly from wet to dry and the avalanche potential increased rapidly. This points to increasing danger with elevation. The nature of this weak layer can allow for wide propagation and triggering avalanches remotely, including from below.

Although it has been raining from ~1,700′ and below with wet snow falling up to ~2,500′, we have seen little wet avalanche activity. The rain has wiped out the snow cover below 1,500′, but in the elevation band from 1,500-2,500′ the snowpack goes from 0-2′. The main concern for wet avalanches is the new heavy snow (10-12″) sliding on the old hard surface underneath. I was able to trigger a push-a-lanche yesterday on a slope ~40deg. Avoiding steep slopes at these wet snow elevations, including runout zones from steep slopes above you, is recommended as this wet storm continues.

As we go into Wednesday, temperatures are forecast to cool. If this is the case, the mid-elevations will begin to freeze and wet avalanche potential will decline.