By Saturday, new snow and strong wind is expected, increasing overall avalanche hazard. The forecast predicts strong wind and moderate amounts of snow through Sunday, Feb. 19th. Near surface facet growth in the top 20-30 cm of the pre storm snowpack may dramatically increase the hazard with enough snow and/or wind loading.
On Feb. 13th, an avalanche crown was observed on ~NW slopes of Core Ridge below treeline. This looks like a storm slab that likely released sometime during the Feb. 11/12 storm cycle (see below photo). Cracking and collapsing wind slabs were observed on February 14/15 on westerly and southwesterly slopes of Temptations Chutes and Agassiz Peak. Some minor roller ball activity was observed on steep (>45°) ~southerly slopes in the Humphreys Cirque area on Wednesday, February 15th. Wind loaded southwest aspects may be reactive, especially above treeline.
Surface hoar was observed on northerly slopes, below treeline in the Inner Basin. Wind associated with the next storm may destroy these beautiful weak layer crystals. However, in wind sheltered locations, buried surface hoar may act as a persistent weak layer.
Last weeks warm spell has densified most of the snowpack, more so on southerly and sun exposed aspects. New weak layers will most likely be established in the Feb. 11/12 snow due to a strong temperature gradient in the upper 20 - 30 cm of the existing snowpack.
Spring-like on Wednesday and Thursday, February 15-16, have helped settle instabilities associated with this past weekends storm snow and initiate a melt freeze cycle. Instabilities may still exist in steep terrain loaded by the northeasterly winds of Feb. 14/15th, with wind slabs and cross loading developing on west and south aspects near and above treeline.
Near and Above TreelineThe storm forecast for Saturday and Sunday, February 18-19, may create new storm and wind slabs. Time is needed for the new snow to bond with the snowpack below. Most avalanche accidents occur within 24 hours of new snow.
The wind slabs that developed on west and southerly aspects on Feb. 14/15 may become more sensitive with additional snow and wind loading. In some places, these slabs may be resting on weak near surface facets that started developing when last weekend's cold snow settled onto a warmer snowpack. The warm/cold imbalance created a temperature gradient that allowed for facet growth. Recent pit analysis reveals a lingering strong temperature gradient in the top 20 -30 cm of the snowpack. Facets will continue to develop 20 - 30 cm below the old snow surface, potentially creating a persistent weak layer upon which new storm and wind slab will rest. New snow may be too much for this newly forming weak layer, possibly resulting in natural and human triggered avalanches.
Below TreelineOn Wednesday and Thursday, February 15-16, soft recrystallized powder snow could be found on shady north aspects below treeline. Sun and radiation affected slopes developed melt/freeze crusts, along with reports of good corn snow and spring skiing.
Coverage is great above 9000'. The warm temps have melted much of our snow below 8000', especially on sunny slopes.
New snow may create storm and wind slabs, especially above treeline. Even with light precipitation amounts, wind can deposit significant amounts of snow on leeward slopes, as well as cross load gullies and chutes. Forecasted warm temperatures for February 20-22 may increase slab failure potential as the temperature rises.
Wind slabs usually stabilize in less than a week. Reduce your exposure to avalanche hazard 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, have signs of fracturing, cracking, or whoompfing sounds.
Cold new snow falling on a warm snowpack may set up an environment for rapid production of tiny near surface facets at the interface. The snowpack has gained some heat the past two days, especially 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.
Winter travelers are urged to pay particular attention to how well new snow accumulating February 18-19, bonds with the old snow below.
If new snowfall reaches or exceeds maximum depths forecasted, storm slab avalanches 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.
Storm slab avalanche crown line (arrow) with debris below observed on Monday, Feb. 13th. This likely occurred during the Feb. 11/12 storm. Photo by Josh Langdon.
This season's snowfall has provided excellent backcountry opportunities! Maintain safe travel practices and remain flexible with tour planning to accommodate signs of instability.
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.
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 Thursday, February 16, 2017.
The precipitation of Feb. 11/12 delivered a nice refresh to the peaks. It appeared that the inner basin received more snow than the western side of the peaks, with the Inner Basin SNOTEL reporting about 12 inches of new snow, and about 1.5 inches of new snow water equivalent. The system also brought much needed colder temperatures, refreezing our wet and warm snowpack.
Feb.14/15 delivered sustained winds of 10-30 mph from the NW through NE, and by Thursday, Feb. 16th temperatures rebounded with about 10° (F.) above seasonal average.
Starting Friday and continuing through the weekend, a period of cooler and unsettled weather will affect northern Arizona with occasional rain and high elevation snow showers. Near treeline, 10 to 20 inches of new snow is predicted, along with strong westerly, southwesterly and southerly winds.
Fair and mild weather is expected by Monday/Tuesday, and by Wednesday increasing clouds and slight chances of precipitation return.
Weather station information: On the Thursday, February 16th, the Inner Basin SNOTEL site (Snowslide Canyon) reported a snow depth of 76 inches (193 cm) at 9700’, and Arizona Snowbowl reported 83 inches (211 cm) at 10800’. Since February 11th, SNOTEL temperatures ranged between 14° and 49° F, and Agassiz station between 19° and 34° 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 firstname.lastname@example.org.