Dangerous and reactive wind slabs exist above treeline on the San Francisco Peaks. Travel in wind loaded terrain is not recommended.
Evidence of natural avalanches were seen in Humphrey's cirque and reports came in that a 6 ft crownline was observed in Snowslide Canyon. These most likely ran sometime between Saturday and Monday during our winter storm trifecta, January 20-23, 2017. This storm cycle produced 93" of snow and almost 7" of water, which is a significant weight on the previously fragile snowpack.
Reactive wind slabs are actively forming near and above treeline. Human triggered and natural avalanches are possible in wind affected terrain.
Avalanche starting zones above 1st and 2nd Gully, on Agassiz Peak are wind loaded and have reactive hard wind slabs. This terrain is easily accessed from the top of the Agassiz Chairlift at the Arizona Snowbowl. The backcountry access point at the ski area is at treeline, which obscures the view of the loaded slide paths above. Hard slabs are a common cause of avalanche fatalities, particularly those involving traumatic injuries. Wind slab avalanches can be triggered naturally by wind loading, which is currently occurring, or by the weight of a skier or rider.
Trend: Considering the cold temperatures we are currently experiencing, wind slab reactivity may linger longer than usual.
Conditions will improve, but the question is how long will this take? Travelers should exercise caution by avoiding wind slabs for the next week. Even after that, we recommend carefully accessing wind slabbed slopes by performing propagation tests like the Extended Column Test (ECT) and the Propagation Saw Test (PST) before deciding to ride. Remember that wind slab by nature are highly variable in thickness. Test wind slabs in areas thought to be thiner, therefore weaker and more prone to human triggering to void false positive results.
Near and Above Treeline:Earlier this week, northwesterly winds stripped new powder from northerly aspects and loaded ~NE through ~SE terrain. Currently, strong northeast winds from 30-50 mph are loading southwest facing terrain.
Some reactive soft windslabs (fist+ to four finger-) were found near 12000 ft on easterly slopes of Humphrey's Cirque. These are the avalanche slopes often used for the hike/skin out of Humphrey's Cirque to the low saddle and back to Az Snowbowl. In some spots along the skin track where the slab was harder, we observed windslab propagation potential in some quick pits. ECTP10, sudden collapse about 15cm down. Fortunately the slab hardness was quite variable, mostly soft, and not very consistently cohesive. However these windslabs have matured and become more consistently reactive with the continued winds.
Negative 30°F or less windchills have been reported today at the Agassiz Weather Station. COLD.
Some cornice formation was observed, and perhaps growing with the persistent winds... keep this in mind as you near steep ridgetop edges for a closer look.
Below Treeline:The powder below treeline is great. The sun has affected open southerly slopes at lower elevations. Watch for steep isolated terrain traps in gullys, and buried rocks and logs. Coverage is excellent down to 7000 ft.
Optimum wind speeds for the transport of snow are currently in progress, and there is plenty of snow available to move. Wind Slab avalanche hazards will continue through the weekend, primarily near and above treeline. With the current NE winds, watch for loading of SW slopes, and cross loading of NW and SE facing gullies and chutes. Travel in or below wind loaded terrain is not recommended.
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. These are all indicators of a slab overlying weaker snow beneath, and potentially hazardous conditions.
Numerous rescues were conducted this week by the Coconino County Search and Rescue, and the Arizona Snowbowl Ski Patrol. Current avalanche danger, low temperatures, high winds, and deep snowpack make rescue very difficult and perhaps not possible. Evaluate your travel plan and emergency preparedness before travelling into the backcountry, or wait until conditions are more favorable for backcountry travel.
Travelers are advised to exercise caution and make slope specific evaluations. 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. They are filling up fast!!!
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
In the aftermath our 10th most productive storm cycle on record, cold air is flooding into the region. Temperatures over the last week have been cold, and for the short term these will continue. Blustery northeast winds will move some snow onto southwest slopes and cross-load gullies. Wind chills of well below 0° F will prevail on Friday and Saturday creating dangerous cold injury travel conditions. Ridge top winds of 30 to 40 mph and higher gusts are forecasted.
Gradual warming will start on Sunday and continue through most of the week. Several minor disturbances are on the horizon for late in the week, but at this point these seem to lack sufficient moisture to produce significant precipitation.
Weather station information:
On the morning of Friday January 27th the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 85 inches (216 cm) at 9700’, and Arizona Snowbowl reported 105 inches (162 cm) at 10,800’. Since January 21th, SNOTEL temperatures ranged between 1° and 34° F, and Agassiz station between -5 and 22° F.