We have received significant accumulations of snow over the last 4 days, and especially the past 24 hours. Moderate and strong winds blew from the south, southwest and west. Natural avalanches are likely and human triggered avalanches are very likely. Travel in avalanche terrain is not recommended. Play it safe - stay off and do not get under slopes that are greater than 30°.
Buried persistent weak layers have been re-energized. The below video is from Monday, February 4th on a 30° NW aspect near Alison Clay Bowl.
Near and Above Treeline:Watch for new wind slab development on north, northeast and east aspects. Post storm winds may create slabs on other aspects. As always, watch for cross loading in gullies.
On January 31st, surface hoar was observed near/above treeline on Agassiz Peak. Watch for new slab development above preserved surface hoar, these will be particularly reactive.
Prior to this week's precipitation, wind scoured zones reduced the snowpack down to bedrocks in some areas. Also, sun and wind conspired to create hard snow prior to recent precipitation . Crampons may be helpful where new snow has been wind-scoured down to hard icy snow.
Below Treeline:Persistent slab instabilities exist in our snowpack. A reactive, faceted weak layer exists about 30 to 50cm from the ground, primarily on northwest, north and northeast slopes, near treeline and below. Carefully assess run out zones and terrain traps.
Watch for new wind slab development on north, northeast and east aspects. Post storm winds may create slabs on other aspects. As always watch for cross loading in gullies. Slopes just below ridges and on the flanks of shoulders should be considered suspect.
Keep an eye on the ASBTP weather station. Readings between 15 and 35 mph indicate the potential for snow transport and formation of wind slabs. Look for various links under the weather menu above. Note that this station may get rimed during storms and report erroneously.
Column test in Beard Canyon on January 11th and near Alison Clay Bowl on February 4th indicating persistent slab problems.
This problem has been found near and below treeline on northwest, north and northeast aspects.
Weak faceted snow-layers under old wind/storm slabs exist at elevations above 10,000'. Stability tests have revealed this problem on northerly aspects with our most reactive failures occurring near and below treeline.
Storm Slabs form when new snow consolidates over a weaker layer or interface. The weak point can be snow that fell early in the storm or just a poor bond with the old snow surface. Storm slabs commonly form during periods of light or no wind. They can be very sensitive to failure, but the problem is usually short-lived, soon bonding to the snowpack below.
The bullseye slope angle for avalanche activity is 38 degrees. Moderating slope angles to 30 degrees and less drastically reduces the likelihood of triggering an avalanche.
Storm slabs tend to stabilize relatively quickly. Waiting at least 24 hours after significant storms is always prudent. Waiting longer is even better.
Storm slabs gain strength and bond with the old snow below, resolving much of the problem.
See our courses page to register for a class and get avy savvy.
Backcountry permits are required for travel in the Kachina Peaks Wilderness and available at local USFS locations, as well as, at the Agassiz Lodge on Saturday and Sunday 8:30 -11:30.
For information on uphill travel within the Arizona Snowbowl ski area, please refer to www.flagstaffuphill.com and https://www.snowbowl.ski/the-mountain/uphill-access/ for details. Access to the Kachina Peaks Wilderness is available from the lower lots at Snowbowl via the Humphreys Trail and Kachina Trail.
Wednesday, February 6th Update:
Arizona snowbowl (10,800') reports 41" since Saturday, and 19" in the last 24 hours. The Snowslide SNOTEL (9,730') reports 22" since Saturday, and 9" in the last 24 hours.