Springtime conditions and the potential for new snow mid week may lead to wet loose avalanches and storm slabs. Dangerous human triggered avalanches are possible but unlikely until new snow falls, with the exception of wet slides due to warm temperatures. Skiers or boarders could trigger or get caught in wet loose avalanches during the afternoon melt. These could pose hazards by knocking travelers off their feet and washing them into terrain traps. Larger wet slab avalanches are also possible during the warmest afternoons on southerly and southwesterly aspects as unseasonably warm temperatures introduce a lot of melt-water into the snowpack, breaking bonds between grains and pooling at impermeable crust layers or density breaks. Such conditions can quickly form weak layers upon which the weakened snow above slides.
With record warm temperatures, wet slides have been reported in the Humphrey's Cirque on the south east aspect. Two point release wet avalanches occurred on March 9 in the afternoon. The track of the slide ran from below solar affected cliffs through smaller chutes and covered previous ski tracks.
On Tuesday and Wednesday a pattern change will bring wind, cooler temperatures and increasing chances of precipitation. If new snow loads exceed current forecasts, storm and wind slab avalanche danger will rise. Snow water equivalent (SWE) of more than 1 inch, or 12 inches of new snow in 24 hours are good threshold markers of concern.
Instability of new storm slabs, or the development of a new weak layer may become an issue as near surface facets are formed at the interface of new and old snow. There is a lot of heat built up in our snowpack from last week, setting up the scenario of vapor flux from the warm snowpack to the new cold snow, forming a wafer thin layer of near surface faceted crystals (NSF). Prior to planning a back country tour, refer to temperature trends from the Agassiz Peak Station to insure consistent freezing in the snowpack, which provides cohesion during melt freeze cycles. Freeze episodes of shorter duration influence the likelihood of wet slides within loosely bonded snow.
Near and Above Treeline:Other than wet loose and slab avalanches described above, ridge-top cornices should be treated carefully. Warm temperatures soften and weaken cornices, making these more likely to break, naturally and under a person’s weight. New snow may create new avalanche problems, so keep an eye on precipitation rates and loads during the next storm.
Below Treeline:At lower elevations the snowpack has matured, gaining density and becoming isothermal. Under these conditions, it stiffens and gains strength during the cool of night, and warms and becomes increasingly sloppy and wet during the day. These cycles of melt/freeze progression tend to make the snow cover more stable over time. These conditions make human triggered avalanches below treeline unlikely, except on steep sun exposed slopes, or the isolated steep areas of gullies. Skiing and boarding conditions are variable by aspect and time of day, with southern and westerly facing slopes most prone to sloppy afternoon sloughing.
As warm spring temperatures take hold, watch for deep slush, snowballing, pinwheels, and small wet slough indicating the potential for larger wet sloughs or wet slab releases. Keep an eye on the Agassiz Weather Station which is near treeline. If overnight temperatures do not drop below freezing then wet avalanche hazard will increase near treeline.
Quick warming after new snow can cause wet avalanches. Rain on snow can cause wet avalanches.
This weekend and into early next week warm temperatures will continue, prolonging wet avalanche concerns.
New snow and wind on Tuesday, Wednesday and potentially later in the week will increase the chances of wind slab avalanches. Even small snow accumulations with wind can create problems on leeward or cross loaded slopes.
Watch for storm and wind slabs building on a weak layer of near surface facets, which may form as water vapor moves from the warm snowpack to the new cold snow.
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, have signs of fracturing, cracking, or whoompfing sounds.
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.
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
Last updated on Thursday, March 16, 2017
The last week was unseasonably warm with low elevation temperatures 15-20° F above average. On Tuesday, March 14th, a record breaking high temperature of 70° F was recorded at Flagstaff’s Pulliam Airport. Agassiz Peak Station (11500’) recorded a high temperature of 51° F, and Snowslide SNOTEL recorded 61° F on that day. Between 9:15 am on March 13th and midnight on March 15th, night time temperatures barely dropped to freezing. Overall, the spring like weather has added a lot of heat to the snowpack and eliminated temperature gradients within it.
Anticipate windy conditions starting on Monday with light to moderate snow above 9000’ with a maximum of 1 inch of snow water equivalent (SWE) on Tuesday/Wednesday. This mid week low-pressure system may represent the return to a wetter weather pattern, with increasing likelihood of more precipitation by the end of the week and onto the beginning of next week. Considerable uncertainty still exists, so keep an eye on weather forecasts as they are updated during the work week.
On Thursday evening, March 16th the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 70 inches (178 cm) at 9700’, and Arizona Snowbowl reported 91 inches (231 cm) at 10800'. Since March 3rd SNOTEL temperatures ranged between 27° and 59° F and Agassiz station between 22° and 56° F.