Natural and human triggered avalanches seem unlikely until Saturday afternoon when new snow and wind may increase the avalanche hazard. The forecast predicts strong wind and light to moderate amounts of snow through Monday.
On Friday, February 10th, a small windslab avalanche crown line was observed near 10500' on ~NE slopes of Cleaver Ridge in the Inner Basin. It looked less than 10 days old, but we are unsure.
There were reports on February 10th of small wet avalanches triggered by skiers on the warm southerly slopes of Core Ridge. We anticipate a decrease of wet snow reactivity above 10000' over the next 24 hours. It may become an issue again by next Thursday, February 16th.
Warm temperatures did not appear to produce widespread wet avalanche activity on Friday, February 10th, possibly due to breezy conditions helping to evaporate excess moisture on the snow surface. Aside from rapid midday warming creating unstable wet snow, the unseasonably warm temperatures have contributed to snowpack bonding, strengthening and densification.
We continue to find evidence of some poor structure in our snowpack, but high strength and generally low reactivity during stability tests leads us to conclude that avalanches are unlikely. However, new snow and wind may create slabs over the weekend, increasing their likelihood.
Pit data from last weekend.
Near and Above Treeline:Hard snow and ice may be your primary hazard. Watch your footing. Ice axes and crampons may prevent a slide for life on steep, slippery and hard slopes. Watch for new storm/wind slab development with this coming weekend weather activity. Time will be needed for the new snow to bond with the compacted snowpack below.
Below Treeline:You may find some soft recrystallized powder snow on shady north aspects, but you will likely also find wind affected or sun affected snow. Sun and radiation affected slopes have developed melt/freeze crusts. Lower elevation (<10000') snow has become wet and isothermic at lower elevations. Cooler temps over the next few days should encourage refreezing.
Current forecast calls for cooler temperatures, and by Saturday, wet slide potential will drop to improbable.
Coverage is great above 9000'. The warm temps have melted much of the "POTUS Inauguration Trifecta Storm" snow below 8000', especially on sunny slopes.
Not much snow is available for transport near starting zones.This may change with the forecasted precipitation over the weekend. Watch for the development of storm slabs and wind slabs. Even with light precipitation amounts, wind can deposit significant amounts of snow on leeward slopes, as well as cross load gullies and chutes. If we get a warm up after the weekend storm, then watch for slab destabilization as the temperature rises.
Wind slabs usually stabilize in less than a week, so you can reduce your risk by waiting several days after a big loading event.
Always keep in mind, wind slabs are unpredictable, and may support the weight of a skier or rider initially, and fail suddenly with tragic consequences. Avoid snow surfaces which are recently loaded, sound hollow, and look for signs of fracturing, cracking, or whoompfing sounds.
Cold new snow falling on warm snowpack may set up an environment for rapid production of tiny near surface facets at the interface. The snowpack has gained a lot of heat over the past several days, reaching near isothermal conditions on sun exposed slopes at higher elevations, and on many aspects below 10500'. The addition of cold snow on top will create a favorable environment for rapid near surface facet growth. This will delay bonding between new snow and the snowpack below and potentially create a persistent weak layer at the boundary between the new and the old.
If new snowfall reaches or exceeds maximum depths forecasted, storm slab avalanche may become likely. The development of near surface facets at the boundary of new and old snow could turn a storm slab concern into a persistent slab problem. Winter travelers are urged to pay particular attention to how well new snow, accumulating this weekend, bonds with the old snow below.
This season numerous rescues have been conducted by Coconino County Search and Rescue, and the Arizona Snowbowl Ski Patrol. Some of these could have been avoided by better planning and preparation.
Travelers are advised to exercise caution, make slope specific evaluations and most of all, know where you are going and be prepared for the unexpected.
As always, please treat this summary with appropriately guarded skepticism, make your own assessments, and contribute to our body of knowledge by reporting your observations.
Arizona Snowbowl uphill policy.
Want to learn more safe backcountry habits? KPAC offers level I and II avalanche courses. There is one class left this season.
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
Last updated on Friday, February 10, 2017.
After a cloudy, cool and moist start last week, high pressure moved in on Wednesday and Thursday bringing temperatures 10 to 20° F above normal to northern Arizona. Above freezing temperatures were recorded at the Agassiz Peak Station (11500') between 8 pm on February 8th and the time of publication of this summary on February 10th. A 46° F high temperature was continuously recorded for most of Thursday afternoon at the Agassiz Peak Station while the Snowslide SNOTEL ramped up to a scorching 55° F during the same period. Winds have been light and variable, primarily out of the west and northwest, shifting to southwesterly and gusting into the low teens on Thursday afternoon.
As the weekend arrives, so does a low pressure system and cold front, bringing cloudy skies, a cooling trend and light to moderate high elevation snowfall. These conditions will last through the weekend. Snow accumulation is expected to range between 8 and 14 inches at elevations above 10000' accompanied by southwesterly winds of 20-35 mph.
High pressure is expected to return and build through next week with seasonally normal temperatures and clear skies.
Weather station information:
On the morning of Friday February 10th, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 71 inches (180 cm) at 9700’, and Arizona Snowbowl reported 79 inches (201 cm) at 10800’. Since February 3rd, SNOTEL temperatures ranged between 29° and 55° F, and Agassiz station between 19° and 46° F.