Natural wind slab avalanches from last weekend’s wind event were spotted on Monday.
Natural wind slab avalanche on west aspect of ridgeline between Skyscraper and Granite Mtns.
Natural wind slab avalanche on east aspect in cross loaded gully directly north of Martin
Persistent weak layers in the snowpack still exist, but are slowly stabilizing over time. While the likelihood of triggering a slab avalanche is decreasing, the possibility is still present, and the consequences could be high. The likelihood of triggering an avalanche will be greater above 3000’, on all aspects, on slopes 35° and steeper.
The snowpack depth is highly variable, from 1-5 feet deep, with the deepest snowpack at upper elevations, on West to North aspects, due to wind loading through the season. Triggering an avalanche on these leeward aspects will be more consequential than windward, shallower aspects due to the amount of snow involved. Windward aspects are scoured down to rock and tundra in many location above 3000′.
On leeward aspects along ridgelines and cross loaded features, a hard 2-10″ thick slab has been deposited by last weekend’s winds. This slab can be found sitting on loose, faceted snow. Observers on Tuesday reported whumphing on a set-up like this in Upper Willow Creek. On Wednesday, these slabs were found to be stubborn to unreactive on North aspects between 4000-4500′.
One of the biggest things we can do to increase our margin of safety is to choose slopes with gentle fanning run-outs and avoid terrain traps. Unsupported slopes in steep, shallow, rocky terrain will be more likely to harbor the avalanche problem.
Keep in mind that the poor structure of our snowpack won’t be going away anytime soon, and any new rapid load may re-activate weak layers in our snowpack.
Snow pit in Upper Willow Creek on Skyscraper’s west aspect showing our widespread poor structure: a dense slab sitting on two distinct layers of weak, faceted snow at the base of the snowpack.
Old natural persistent slab avalanche from New Years wind event on north aspect of Peak 4600′, north of Gov’t Peak. Large avalanches like this are still possible to trigger, especially on steep, rocky, unsupported slopes above 3000′.
Hard 2-10″ thick wind slabs have formed over loose, faceted snow in places. Whumphing was reported by observers in a spot where this structure was found.
Weather at 3450′ since Saturday 1/12:
Temperatures averaged 28°F, with a low of 14°F and a high of 34°F.
There has been no new precipitation.
Weather at 4500′ since Saturday 1/12:
Temperatures averaged 25°F, with a low of 10°F and a high of 32°F.
Winds averaged SE 8 mph, max 21 mph. Gusts averaged SE 14 mph, max gust 43 mph.
Stay tuned to the NOAA point forecast for an updated weather forecast each day. The best way to see if it’s snowing in Hatcher Pass is to look at the webcam snow stake HERE and the Independence Mine SNOTEL site HERE
State Parks Snow Report and Motorized Access information can be found here.