Island Park

Small natural storm slab

This avalanche started on a slope above the rocks where there was more wind and then triggered another storm slab in the trees. It created a significant debris pile.

Light red lines indicate crown faces of this natural avalanche. It likely started as a wind slab/storm slab above the rocks, then dropped down onto the slope below triggering a storm slab avalanche that entrained a significant amount of snow and created a big debris pile.

We rode to the top of Sawtelle to de-rime the anemometer (wind sensor) and then down into Rock Creek Basin under all the big north facing avalanche paths.

Key findings:

1. New snow amounts ranged from 6-8" at lower elevations and 18" at higher elevations
2. We did not observe any cracking or collapsing on non wind loaded slopes.
3. We observed two very recent natural storm slab avalanches about a 1.5 feet deep. One of them entrained a significant amount of snow an ran a long ways.
4. There has been minimal wind effect except at ridgetops
5. Extended Column tests on north facing slopes continuously broke and propagated after 12 taps (ECTP12) just under a soft crust in snow that fell last weekend. These appeared to be breaking on broken stellars/snowflakes. On other aspects, the crust was much thicker and harder.

Conclusions:

The likelihood of triggering a soft slab avalanche about 1.5' deep seemed low on non-wind loaded slopes. Any amount of wind affecting a slope whether loading a slope or just stiffening the new snow, dramatically increased the odds of triggering a slide. We felt comfortable riding in avalanche runout zones and even climbing into the paths some. The main strategy was to stay out of the upper starting zones that are steeper and have seen some wind. HOWEVER - we carefully limited our exposure in big runout zones where a falling cornice could have triggered a slide that could have crashed down onto us. We did not think that we would trigger an avalanche from below  

Looking ahead  - Strong winds Sunday through Monday will have plenty of snow to transport along with additional snow that will fall. This should increase the danger and the size of possible avalanches.

From phone call:

Kevin took a group into the Centennials.

8" of new snow at 8000'. Surface crust below the new snow was 3 CM thick. There was a facet layer below crust that was concerning. ECTN3 below crust. 

Kevin found the January facet layer 90 CM down (4F hardness) a couple miles north of White Elephant at 7800-7900' (0.5-1mm size). No results in tests but was concerned about their activation if the storm snow start stacking up.  

He noted that the Wind Slab and Storm Slab problems are growing. He saw shooting cracks in the new snow, several feet in front of his skis. 

Winds were light to moderate but gusting into the 20s mph. 

We rode from the Sawtelle Parking area up the shoulder of Sawtelle, across Yale Creek and above East Hotel Creek, through Jefferson Bowl, into Hellroaring Creek drainage to the base of Reas before reversing the order and heading out. We saw no avalanches and no signs of instability. Three snowpits (above East Hotel, in Jefferson Bowl, and above Hellroaring) revealed nothing remarkable - ECTXs and ECTNs in the 20s. The south-facing pit above East Hotel had many crust facet sandwiches, but none are currently an issue. It would take a significant load to bring up any concerns about avalanches breaking on persistent weak layers deeper in the storm. 

Stability is good. There are tracks everywhere, and we are looking forward to a reset, hopefully arriving Wednesday night. Most slopes have a melt-freeze crust at the surface. There is no remarkable weakening at the surface to note at this point. Unless something changes between now and Wednesday, instability should be limited to the incoming snow and wind-drifted snow. 

8-12 inches of new snow on the ground in the Centennials near Nemesis mtn. New snow that fell early this morning was very touchy on hard/icy surfaces from the melt/freeze activity we saw the prior days.