Avalanche hazard will start increasing Saturday afternoon, February 2nd.
Today (Friday, February 1st) natural and human triggered avalanches are unlikely. By Saturday afternoon, new snow accompanied by southerly and westerly winds will increase the likelihood of human triggered avalanches.
The potential for a more significant and colder system remains on the table for Tuesday and Wednesday, and avalanche hazard may stay elevated this week.
Persistent buried weak layers could be re-energized by the load of significant new snow. New snow loads of more than a foot in 24 hours, or 8 inches in 12 hours with wind are causes for concern. Please make slope specific evaluations by digging test pits and performing stability tests, especially if the forecasted storm fall materializes.
The past week has been dry and breezy. High sustained wind between 15-35 mph occurred on January 26, 27 and 28th. The strongest winds were out of the northeast, shifting to the north and moderating as the week progressed. Gusts over 50 mph were recorded on all three of these days. Loading of windblown snow was limited by the ever increasing lack of snow available to transport, as most of it is already packed into hard wind slab or returned to the atmosphere from the impressive wind events the week prior. Still, snow plums were observed on the ridge tops potentially loading southwest and south facing slopes at and above treeline.
Snowpack stability tests indicate poor to moderate structure, moderate strength and moderate to low energy. Recent temperature gradients may indicate a transition from building weak facets to general strengthening of the snowpack. New precipitation could load the snowpack sufficiently to cause a failure.
Near and Above TreelineMany alpine slopes have been scoured by winds (photo below). By Saturday evening and Sunday, watch for new wind slab development on north, northeast and east aspects. Post storm winds may create slabs on other aspects. As always, watch for cross loading in gullies. The new snow may have a hard time adhering to relatively slick hard-snow and crusts.
Surface hoar (photo below) has been observed near treeline. Watch for new slab development above preserved surface hoar, these will be particularly reactive.
Snow depths near and above treeline range from 51" (130cm) to 0. Wind scoured zones have reduced the snowpack down to bedrocks in some areas.
Sun and wind have conspired to create hard snow. Crampons may be helpful.
Below TreelinePersistent slab instabilities may still exist in our snowpack. A reactive, faceted weak layer exists about 30 to 45cm from the ground, primarily on northwest, north and northeast slopes, near treeline and below. Carefully assess run out zones and terrain traps.
Currently 20" to 40" (~50 to 100 cm) of snow cover can be found between 9,000 and 10,000', with more above.
Due to low elevation rain and warmth, the snowpack rapidly diminishes below 8,000', especially on sunny slopes.
Current forecast for snow and wind suggest wind slab hazard will become and issue by Saturday evening and Sunday morning. Watch for new wind slab development on north, northeast and east aspects. Post storm winds may create slabs on other aspects. As always watch for cross loading in gullies.
New snow may have a hard time adhering to relatively slick hard-snow and crusts that exist near and above treeline.
Slopes just below ridges and on the flanks of shoulders should be considered suspect.
Keep an eye on the ASBTP weather station. Readings between 15 and 35 mph indicate the potential for snow transport and formation of wind slabs. Look for various links under the weather menu above.
Our persistent slab problem danger has decreased over the last week or so. However, new snow plus a human trigger may be enough to collapse a persistent weak layer on some steep and isolated slopes, primarily near and below treeline on northwest, north and northeast aspects.
Weak faceted snow-layers under old wind/storm slabs exist at elevations above 10,000'. Stability tests have revealed this problem on northerly aspects with our most reactive failures occurring near and below treeline.
Storm Slabs form when new snow consolidates over a weaker layer or interface. The weak point can be snow that fell early in the storm or just a poor bond with the old snow surface. Storm slabs commonly form during periods of light or no wind. They can be very sensitive to failure, but the problem is usually short-lived, soon bonding to the snowpack below.
New snow may have a hard time adhering to relatively slick hard-snow and crusts that exist near and above treeline.
The bullseye slope angle for avalanche activity is 38 degrees. Moderating slope angles to 30 degrees and less drastically reduces the likelihood of triggering an avalanche.
Storm slabs tend to stabilize relatively quickly. Waiting at least 24 hours after significant storms is always prudent. Waiting longer is even better.
Storm slabs gain strength and bond with the old snow below, resolving much of the problem.
Surface hoar observed on Agassiz Peak above treeline, Thursday, January 31st. Watch for preserved surface hoar buried by new snow, as this would become a reactive weak layer. Photo by Paul Dawson.
Above treeline wind scour in Alison Clay Bowl. January 31st photo by Paul Dawson.
Weather updated Friday morning, February 1st. Over the past week, a high pressure ridge dominated our region, with a couple of short wave lows moving though, bringing clouds and breezy conditions, but little or no accumulation of new snow.
Thankfully, the high pressure ridge seems to be breaking down, allowing a series of storms to move into Arizona. The first of these came last night, with light to no precipitation. No new snow was reported at 10,800 feet at Arizona Snowbowl. More snow is in the forecast for the weekend with a moister and more dynamic storm arriving on Saturday night and lasting through Sunday midday. Although the exact track of this storm is still poorly defined, 12 to 18 inches of new snow near treeline is possible. The snow line will start high, at about 8000 feet, and drop to 5500 feet as the storm progresses. As much as 0.75 to 1.5 inches of snow water equivalent (SWE) could load our snowpack. Unsettled weather is predicted to continue throughout the workweek, but numerical prediction models are disagreeing on timing and precipitation potential.
On Friday morning, February 1st, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 31 inches (79 cm) at 9,730 feet. Arizona Snowbowl reported a settled base of 47 inches (119 cm) at 10,800 feet. So far this winter, 128 inches (325 cm) of snow have fallen at the mid-mountain study site. Since January 25th, SNOTEL temperatures have ranged between 13°F on January 26, and 46°F on January 27th. For the same period, the AZ Snowbowl Top Patol Station (ASBTP 11,555 feet) temperatures ranged between 12°F on January 26th, and 37°F on January 28th.
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.