New Snow poses renewed avalanche problems. Prior to the Thursday January 9th evening storm, accumulated evidence has suggested that human triggered avalanches were generally unlikely. Many surfaces above treeline were stripped with multiple high wind events in recent weeks. Surfaces ranged from very firm on wind affected aspects above treeline to breakable crust on sunny aspects and some pockets of soft snow on northerly slopes. However, Thursday's storm has brought 9 inches as of January 10 on top of these previous surfaces. Remember, yesterday's snow surface can be today's weak layer or bed surface.
Pit data from January 4th through Friday, January 10th has continually suggested a complex, weak structure in the snowpack without significant energy on many aspects. Some pits have shown propagation propensity but this has, thus far, shown to be inconsistent indicating pockets of energy in the snowpack. The structure of the snowpack has remained consistently poor, particularly on northerly aspects. Weak layers surrounding several ice lenses have been persistent, particularly where the snow temperatures remain cold.
As more snow falls, be particularly cautious of wind transport and loading as strong north winds transport the new snow, creating wind slabs on leeward aspects, particularly above treeline. Most avalanches occur within 24 - 48 hours of new snow or a wind event. Persistent weak layers always have the potential to become reactive under new load.
Arizona Snowbowl is reporting 9 inches of new snow at 10,800', Friday, January 10th.
Look for new weak layer formation in the snowpack as deeper weak layers may start to heal. Near surface faceting is possible where melt-freeze crusts formed last week. Look for these new weak layers when evaluating the snowpack and their subsequent stability. Southerly Slopes also have potential wind load from north wind on Friday, January 10. As is often the case, however, wind on the Kachina peaks can move in many different directions locally. Evaluate local terrain for evidence of recent wind transport and be suspicious of leeward aspects from slopes that were stripped of new snow.
We currently have a complex snowpack that is highly variable depending on aspect and elevation. Review the snowpits.
Near and Above TreelineSome aspects, such as the easterly aspects of the Humphrey's cirque and Snowslide bowl, have up to 3m of snow while other aspects above treeline were either stripped or packed down by wind to a very firm surface. Crampons are strongly recommended for mountain travel as the surface conditions were firm and highly variable prior to the January 9-10 storm and with wind are likely to remain so.
Leeward aspects (south and east) from the forecast north and west winds after the storm could have wind slabs overwhelming weak layers both new and old soon after the event. Suddenly 9 inches of new snow is available for wind transport. Carefully evaluate what wind has transported in the area of your intended travel and it's affect on the local snow stability.
Beware of wind transport. Wind can transport snow many times faster than falling snow. Manage terrain and evaluate snow stability carefully as the dust settles from this recent snow and subsequent wind.
Below TreelineSurfaces below treeline prior to the storm ranged from firm to soft to breakable crust. Even with new snow, skiing is likely to be variable from turn to turn. Travel with care and watch for obstacles unseen from new snow. Sloughing is possible, particularly on aspects with a very firm surface prior to the new snow.
Beware of obstacles and highly variable conditions around the mountains below treeline.
Some avalanche danger may exist from wind slab on leeward slopes after the January 10th storm and north wind event. Look for signs of recent wind loading and pay attention to aspect and local wind loading patterns while traveling through the mountains. While South and East aspects are more likely to be loaded, local wind variations can lead to loading on almost any aspect. Evaluate terrain carefully.
Storm Slab releases are possible on aspects not stripped by wind 24-48 hours following the January 9-10 storm producing 9 inches of new snow. This may particularly be true on surfaces that were very firm prior to new snow.
Last week’s weather was a mixed bag. A broad, low amplitude trough parked over the region allowed quick moving, short wave, low pressure systems to track through northern Arizona. These have brought wind, cool temperatures, and overcast skies, but not much precipitation. Between these events above average temperatures were recorded. At high elevations, temperatures in the mid 40° F have created melt/freeze crusts on most sunny aspects. Nighttime temperature inversions were also evident during these periods. On Thursday afternoon and night, one of these short wave lows brought moderate winds out of the southwest and 9+ inches of new snow at 10,800 feet.
Looking forward, it appears that an alternating pattern of unsettled weather and pleasant conditions may persist. Windy, cold weather is predicted for the weekend with below zero wind chill temperatures. Snow showers, but not much accumulation are in rhe forecast for mid-week. If the broad trough breaks down, we may return to a more productive precipitation pattern.
Arizona Snowbowl reported a 61” (155cm) base at 10,800 feet. Snowslide SNOTEL reports a 48” (122cm) snow depth. So far this winter, we have had 138” (350cm) of snowfall at 10,800 feet.
Since January 3rd, SNOTEL temperatures have ranged between 15° F on January 6th and 43°F on January 4th. ASBTP station (11,555 ft) reported a low of 11° F on January 9th and a high of 43° F on January7th.
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.
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.
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.