Turnagain Pass

Girdwood Valley: Skiers triggered storm slab avalanches just over a foot deep on steep rollovers on Notch Mtn. yesterday.

Girdwood Valley: There was recent debris from a large cornice fall on Raggedtop. The cornice appeared to break sometime during the beginning of the 1/6 storm, and It was difficult to tell if the cornice triggered an avalanche in the new snow or not.

Seattle Ridge: Riders reported large shooting cracks on small test slopes in the Seattle Ridge flats, fracturing 2-3’ deep and propagating several snowmachine lengths outward.

Seward Highway: In the past few days, we have also noted debris from natural avalanches along the Seward Highway from Bird to Seward.

Today it is very likely a human could trigger an avalanche 4-6’ deep in the new snow from the past 4 days. With more snow on the way, and rain on snow expected up to 1600’, we are also likely to see some large natural avalanche activity today. Since yesterday morning, we have gotten close to a foot of new snow equaling around an inch of snow water equivalent (SWE) at Turnagain pass and Alyeska, with sustained easterly ridgetop winds of 20-35 mph and gusts to 57 mph. This is just the latest round of snow; we have seen steady precipitation since Wednesday morning bring the following storm totals as of 5:00 this morning:

3-4’ snow equaling 4.6” SWE at the Center Ridge snotel site.

3-4’ snow equaling 4.2” SWE at Alyeska’s Mid-mountain station.

11” snow equaling 0.9” SWE at the Summit Creek snotel site.

Snowfall during the day could bring another 6-10”, with rain levels rising to around 1600’. This active loading will make human-triggered avalanches very likely, and we are anticipating some large natural releases as well. The new/old interface is a mix of surface hoar, near-surface facets, low-density stellar dendrites, and very firm wind surfaces, and we have already seen avalanches propagating wide on these various layers. The snowpack will need time to adjust to this heavy load, and for now travel in avalanche terrain is not recommended. Avoid traveling on or below steep slopes, as we are expecting large avalanches to run far into lower-elevation runout zones today. With another round of heavy snowfall possible tonight, we are expecting to see elevated avalanche danger through tomorrow.

Cornices: With several feet of sticky snow this week, and sustained strong winds, cornices are becoming quite large. Some of these cornices have already failed naturally, and it is likely we will see similar activity as this storm continues.

The Turnagain Pass snotel station (el. 1880′) is showing 3-4′ of snow equaling 4.6″ SWE since Wednesday.

The NWS is predicting 3.3″ snow water equivalent between Saturday and Monday. We are about halfway through the forecast period, and right on track to hit that mark.

We have been tracking a layer of faceted snow associated with the 12/1 rain crust, which is now buried 4-7’ deep, and exists at elevations up to around 2500’. While it has been a while since we have seen any avalanches fail on this layer, the current storm will be putting that weak snow to the test. There is a small chance we could see very large avalanches failing on this layer. While this will be an interesting test, it is of secondary concern today because of the high likelihood of large avalanches failing within the storm snow mentioned above.