A storm last Thursday and Friday deposited 5 inches of snow at 10,800’ and since then conditions have dried out. No natural or human triggered avalanches have been reported. This Wednesday afternoon through Thursday morning brought extreme ridge top winds out of the north and northwest transporting available snow. Gusts of 85 mph were recorded at the ASBTP weather station at 11:10 pm Wednesday night. Snowpack stability tests today (north aspect 11,600') revealed inconsistent results, with moderate strength but varied energy in CT and ECT tests.
Wind speeds above 45-50 mph typically transport available snow aloft, sublimating (evaporating) back into the atmosphere, rather than loading leeward slopes. However, winds of moderate strength, 15-40 mph are effective at loading starting zones along ridge tops and terrain features of south and southeast aspects with the recent loading. Allow at least 24 hours for snow to settle and bond, natural and skier triggered avalanches may still be possible, although they are unlikely except in localized wind loaded terrain.
On lower elevation slopes, and on all slopes that have been scoured by wind or exposed to intense sun, buried obstacles and hazards still exist. Backcountry skiers and boarders will need at least another foot of snow for favorable travel conditions. Arcing your turns without scraping rocks and logs hidden below the surface is a rarity. Early season conditions will continue for at least another week.
Near and Above TreelineRecent observations have shown variable bonding between November/December snow and old basal facets (depth hoar) from October snow. It appears that facet growth may have been slowed by an ice layer at the bottom of snowpack, which may have inhibited vapor flux. Also, depth hoar crystals have started to bond to one another on certain aspects, but facet metamorphism can continue into January.
Our early season shallow snowpack is becoming the persistent problem. Patience is key. Overzealous enthusiasm leads to poor decision-making. New snow accumulation is the first priority and bonding with the layers underneath second. The lack of new snow can give rise to the "scarcity heuristic trap". Because of wind scouring, snow coverage above treeline is increasingly variable. Hidden rocks and other obstacles are common. Ski with early season eyeballs and awareness in order to enjoy the rest of the winter, once coverage improves.
Below TreelineSafe backcountry travel may be challenging due to shallow coverage at lower elevations. Until more snow falls, hidden stumps, logs, and rocks are significant hazards. Regretfully, KPAC cancelled our Level 1 Avalanche Course scheduled for Dec. 14-16 because of insufficient backcountry snow coverage.
High velocity winds from the north and northeast affected the Peaks on Wednesday through Thursday. Gusts exceeded 80 mph. Although there was limited snow available for transport, and winds of these speeds strip and sublimate more than deposit snow, still hard slab avalanches are a possibility . These are likely to be in smaller pockets, but could be triggered by a skier or boarder. Stay off of hollow sounding pillows of wind slab, be aware of whumping and cracking.
Be aware that even small hard wind slab avalanches carry significant destructive force, much akin to being caught in a rock slide of frozen blocks of high density compacted snow.
Hidden Valley Pit dug by Tanner Porter on Dec. 9 showing mild reactivity at boundary between the late November and Early December storms. Graupel was reported at the storm interface in several pits.
See our courses page for upcoming free courses, including a FREE Introduction to Avalanches Seminar at Aspen Sports on January 3.
Backcountry permits are required for travel in the Kachina Peaks Wilderness and available at local USFS locations, as well as, at the Agassiz Lodge on Saturday and Sunday 8:30 -11:30 a.m.
Uphill travel on terrain within the Arizona Snowbowl ski area is still closed. Please refer to www.flagstaffuphill.com and https://www.snowbowl.ski/the-mountain/uphill-access/ for details. Access to the Kachina Peaks Wilderness is available from the lower lots at Snowbowl via the Humphreys Trail and Kachina Trail.
Over the week we have experienced seasonally normal to above normal temperatures. A wind advisory was issued by the National Weather Service (Flagstaff) from Wednesday afternoon to Thursday morning (Dec. 12-13) with the passing of a dry low pressure to our north. The weather station at the top of Snowbowl (ASBTP) recorded sustained winds of over 40 mph between 11:00 pm Wednesday and 9:00 am Thursday. A maximum gust of 85 mph was recorded at 11:10 pm on Wednesday.
The coming week will bring cloudy, but generally dry conditions. A cold Pacific disturbance will move through our region on Monday and Tuesday bringing mountain snow showers, but little chance of significant accumulation. This will be followed by building high pressure and warming, leading to above average temperatures by week's end.
On Friday morning December 14th, the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 12 inches (30.5 cm) at 9,730 feet. Arizona Snowbowl reported a settled base of 26 inches (66 cm) at 10,800 feet. So far this winter, 41 inches (104 cm) of snow have fallen at the mid-mountain study site. Since December 8th, SNOTEL temperatures have ranged between 15°F on December 13th, and 45°F on December 10th. For the same period the AZ Snowbowl Top Patrol Station (ASBTP 11,555 feet) temperatures ranged between 15°F on December 12th and 40°F on December 10th.
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 email@example.com.