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 TreelineOther 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 TreelineAt 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.
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.
The avalanche problem/character describes part of the current avalanche danger. However because we only realease a summary once a week, the current avalanche problem will likely change.
Understanding avalanche problems is essential, because it allows you to determine your approach and strategies to risk treatment. Below are brief descriptions of avalanche problems/characters, and links to detailed information on the problem, formation, patterns, recognition, and avoidance strategies.
Avalanche Problems Explained Also see the North American Danger Scale.
Release of dry unconsolidated snow. These avalanches typically occur within layers of soft snow near the surface of the snowpack. Loose-dry avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs. Loose-dry avalanches can trigger slab avalanches that break into deeper snow layers.
Loose Dry avalanches are usually relatively harmless to people. They can be hazardous if you are caught and carried into or over a terrain trap (e.g. gully, rocks, dense timber, cliff, crevasse) or down a long slope. Avoid traveling in or above terrain traps when Loose Dry avalanches are likely.
Release of a soft cohesive layer (a slab) of new snow that breaks within the storm snow or on the old snow surface. Storm-slab problems typically last between a few hours and few days. Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
You can reduce your risk from Storm Slabs by waiting a day or two after a storm before venturing into steep terrain. Storm slabs are most dangerous on slopes with terrain traps, such as timber, gullies, over cliffs, or terrain features that make it difficult for a rider to escape off the side.
Release of a cohesive layer of snow (a slab) formed by the wind.
Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side.
Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard.
Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.
Wind Slabs form in specific areas, and are confined to lee and cross-loaded terrain features.
They can be avoided by sticking to sheltered or wind-scoured areas.
Release of a cohesive layer of soft to hard snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow.
Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
The best ways to manage the risk from Persistent Slabs is to make conservative terrain choices.
They can be triggered by light loads and weeks after the last storm.
The slabs often propagate in surprising and unpredictable ways.
This makes this problem difficult to predict and manage and requires a wide safety buffer to handle the uncertainty.
Deep Persistent Slab
Release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer, deep in the snowpack or near the ground.
The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
They commonly develop when Persistent Slabs become more deeply buried over time.
Deep Persistent Slabs are destructive and deadly events that can take months to stabilize.
You can trigger them from well down in the avalanche path, and after dozens of tracks have crossed the slope.
Release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers.
Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. They generally move slowly, but can contain enough mass to cause significant damage to trees, cars or buildings. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.
Travel when the snow surface is colder and stronger. Plan your trips to avoid crossing on or under very steep slopes in the afternoon. Move to colder, shadier slopes once the snow surface turns slushly. Avoid steep, sunlit slopes above terrain traps, cliffs areas and long sustained steep pitches.
Release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very destructive.
Avoid terrain where and when you suspect Wet Slab avalanche activity. Give yourself a wide safety buffer to handle the uncertainty.
Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side.
Cornices range in size from small wind lips of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.
Cornices can never be trusted and avoiding them is necessary for safe backcountry travel. Stay well back from ridge line areas with cornices. They often overhang the ridge edge can be triggered remotely. Avoid areas underneath cornices. Even small Cornice Fall can trigger a larger avalanche and large Cornice Fall can easily crush a human. Periods of significant temperature warm-up are times to be particularly aware.
Large cornices are generally rare in Arizona, but they have been observed during very snowy winters.
Release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. The are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.
Predicting the release of Glide Avalanches is very challenging. Because Glide Avalanches only occur on very specific slopes, safe travel relies on identifying and avoiding those slopes. Glide cracks are a significant indicator, as are recent Glide Avalanches.
Glide avalanches are very uncommon in Arizona.
Snowpack Summary Disclaimer
The summaries on this site were written by Kachina Peaks Avalanche Center Board Members. They are based on a broad spectrum of data collected from weather stations, National Weather Service point forecasts and field observation by qualified individuals.
The summaries are not intended to substitute for good knowledge and decision making skills in avalanche terrain. If you have any doubt of stable conditions, please stay away from avalanche terrain. You can usually find good places to go that are not prone to avalanches, such as on low angle slopes away from avalanche run-out zones. If you have any questions about where to find such places, you should consider further avalanche educational opportunities, such as those listed on our education page.
Snowpack Summary – Format and Limitations Statement
Starting in 2012 Kachina Peaks Avalanche Center (KPAC) has publish a weekly Snowpack Summary on our website.
These summaries are currently issued on Friday afternoons. On occasion, we will give storm updates or warnings of rapidly increasing avalanche hazard at more frequent intervals.
Our objective is to reach weekend recreationist, informing this user group of prevailing conditions, but particularly warning of avalanche hazards whenever they are present.
Many people have asked us why we use the format we do, but do not include a danger rating or a hazard/stability rose as many other avalanche centers do around the west.
The National Avalanche Center (NAC) advises small operations like KPAC, who do not issue daily bulletins to not use danger ratings in our snowpack summaries due to the regular but intermittent nature of their field observations and the length of time between issuance of snowpack summaries.
A primary concern is for how conditions can change in the time between publications, potentially giving the public misleading information. At this point, we simply do not have resources to monitor the snowpack at the level necessary to accurately produce more frequent bulletins.
While we understand the benefits of a danger rating using the North American Danger Scale, we also feel that our format encourages people to dig in a little deeper, and spend some time reading what our forecasters are saying. Although the area that we forecast is relatively small, the variability has proven quite large.
Inner Basin conditions are often surprisingly different from those on the more wind-affected western side on the Peaks.
We hope the information that we provide in summaries helps give you a good overview of what is going on out there, and what avalanche problems you should be attentive to, but if there is any uncertainty, then we encourage you to ask questions via Facebook or email@example.com.