Human-triggered avalanches are likely today. Avoid loaded starting zones, wind drifts, mounds of snow, and pillowed areas. These small avalanches may turn large by stepping down and triggering a persistent slab avalanche deeper in the snowpack. Use caution and watch for signs of instability, shooting cracks, and recent avalanches.
Winds will continue to build dangerous slabs, especially on leeward slopes, gullies, and cross-loaded terrain features. Avoid wind-loaded starting zones on steep slopes. Watch for cracking and be aware of hollow-sounding snow--both obvious signs of instability. If large enough, a wind slab avalanche could step down and release a persistent slab avalanche buried deep in the snowpack.
There is a complex mixture of facets in our snowpack. Most often, these are basal facets buried below the Holiday Crust at the bottom of the snowpack that continue to persist on northern-facing slopes. Over the last week to two weeks, instability tests have not produced propagation, including those conducted in pits averaging just 50 cm. Nonetheless, skiers and riders should continue to exercise caution in the starting zones of steep chutes.
In addition, near-surface facets have been found at and below treeline above the Holiday Crust layer in the upper part of the snowpack. With the new snow load forecast today, these could become reactive.
The variable conditions across terrain make this problem difficult to assess, and it is possible that some slopes still harbor reactive layers near and at the bottom of the snowpack. The only way to fully know if this persistent weak layer is still present and possibly reactive is to dig. Given the mostly rocky bed surface strewn across the San Francisco Peaks, this problem could still produce a small to large avalanche capable of burying a skier or rider.
Storm totals so far are 16" report from Arizona Snowbowl and 7" at the Snowslide Canyon SNOTEL. Over 1.4" of SWE has been recorded at the Snowslide Canyon SNOTEL site since yesterday.
Snow pits yesterday yielded ECTP9 @15cm down and ECTP10 @30cm down from the surface. Both of these broke at density changes within the new snow.
Uncertainty remains as the winds and snow yesterday during the day were both lower than forecast. However, winds overnight on were high and likely removed a lot of the snow from above treeline. Forecast for today, 7-11" of snow at 11,500 with high winds out of the southwest 38 to 48 mph, with gusts as high as 75 mph.
Backcountry travelers should also be aware that the persistent slab issue could produce small to large avalanches, especially if a loose avalanche or wind slab were to step down deeper into the snowpack. If this were to occur, this type of avalanche would be much more dangerous as it might release with a crown height of several feet. This could easily result in a large enough avalanche to cause a full burial. The probability of this type of avalanche is low, but north-facing steep chutes and paths are the most probable locations.
Many south-facing slopes and above treeline areas have been stripped to rock over the last few weeks. This new snow will hide many of the rocks and obstacles just below the surface. Ski and ride with care and watch for the remote possibility of small avalanches or funky conditions carrying a skier or rider over steep or rocky terrain.
