Turnagain Pass

After a long stretch of unseasonably cold, clear and windy weather, a warmer storm rolled in yesterday and is peaking this morning. This storm is bringing strong easterly winds and snowfall to between 500 and 800′; rain below this. As of 9am this morning the mid elevations around Girdwood have picked up 18-20″, Turnagain Pass 8-10″ and Summit Lake just a trace. Another 2-5″ is expected through this afternoon. These snowfall amounts are extremely variable and so will be the avalanche danger associated with them. East ridgetop winds have been averaging in the 40’s mph with gusts in the 70’s.

All the classic storm snow instabilities listed below will be today’s main concerns. The size of avalanches will be relative to the amount of new snow that falls. For example, larger avalanches, which are more likely to occur naturally, are expected near Girdwood and Portage valley with the higher snowfall totals. The one exception is if an avalanche steps down into buried weak layers, more on this in Problem #2. New snow is falling on a variety of surfaces, hard wind crusts, old sun crusts, softer snow over harder surfaces, etc. With the warmer temperatures, this can help the new snow to bond to the older snow more quickly, but that’s all to be determined. The next round of snow tomorrow night is likely to hit before any good bonding takes place.

Wind Slabs:  With such strong winds, wind slabs are likely to be releasing naturally in the higher terrain around Girdwood and may release naturally at Turnagain Pass. These could be up to 3′ thick near Girdwood and a foot plus thick at Turnagain Pass. Any new wind slab, regardless of size, should be easy for a person to trigger. Watching for cracks that shoot out from you and stiffer snow over softer snow are the red flags a slab has been found.

Cornices: These should have some new growth and pieces of them could release, triggering an avalanche below.

Storm Slabs:  This storm is coming in cold and leaving warm, creating an ‘upside down’ storm snow situation. This means heavier denser snow is falling on lighter drier snow, which can form a slab over a weak layer setup. Areas seeing close to a foot of new snow or more could see slab avalanches releasing in areas out of the winds and in the trees.

Loose Snow avalanches (sluffs):  Natural dry sluffs are likely to occur in steep terrain and off rocks in the mid and upper elevations.

Wet avalanches:  Low elevations seeing rain on the new snow (around 500′ and below) may see wet sluffs on steep terrain features. These areas are most likely in the Girdwood and Portage Valley areas where more precip is falling.

If you are headed out today, be extra cautious of where you are headed, how much snow has fallen and if there is avalanche terrain above you. Watch for cracking in the new snow and any signs the new snow is acting like a slab.

The National Weather Service snowfall total (ending today at 10am) looks to be coming true for Turnagain Pass, but higher amounts have already been seen in the upper Girdwood Valley. 

New snow, wind loading and warmer temperatures are all factors that can contribute to activating stubborn buried weak layers in the top 3 feet of the snowpack. Hence, avalanches in the new snow could step down to these layers and create a larger avalanche. The Crow Pass and Raggedtop area near Girdwood is a suspect region and has seen this occur over the past few weeks. Additionally, thinner snowpacks with more advanced weak layers are especially likely, such as in Summit Lake south of Turnagain Pass. Summit Lake may not see much snowfall, but the area is seeing strong winds and warming temperatures.