Human triggered wind slab and persistent slab avalanches are possible, natural avalanches are unlikely.
It's now been over 24 hours since snow accumulated from the George Washington Birthday Storm, when 28" of new snow accumulated at 10,800' between February 22-24. Arizona Snowbowl Ski Patrol observed snow transported by southwesterly winds on Wednesday, February 23, then northeasterly winds on February 24. There may still be reactive wind slabs out there, and westerly and northerly winds this weekend may build new ones.
Last weekend on northly slopes, near surface facets were observed under ~4" (10cm) of mid-February snow; see image below. Tests indicated that new cohesive slabs may have the means to propagate a failure-fracture within this weak faceted layer. On Tuesday morning, February 22, an ECTP6 test result indicated unstable snow on a ENE aspect of Core Ridge near 11,400'; see snowpit below. There is a bit of uncertainty with the distribution and sensitivity of this persistent slab problem. Thus far it's only been observed on north, northeasterly and east-northeasterly slopes between 10,400' and 11,500'.
Prior to this storm, many southerly slopes were rock strewn below 11,500.
Looking forward, a warmup after very cold temperatures is expected by midweek. Snowpacks do not like rapid change.
Thin snowpack conditions may still persist and recreationists should remain cautious of obstacles buried by the new snow.
Only very small (R1D1) human triggered and natural avalanches reported this season, occurring within the last eight days of January.
Near and Above Treeline (~10,800' and above)Watch for convex pillows of wind-drifted snow on the lee sides of ridges and other terrain features. Wind Slabs may present a hollow drum like sound as you traverse across slope or send shooting cracks from your skis.
Steep northerly, northeasterly and easterly slopes near and between 10,400' and 11,500' may harbor a persistent slab problem, specifically where new cohesive slabs have developed over ~4" of mid-February snow that overlays weak sugary facets. There may also be a crust associated with this persistent problem (see snowpit below).
Prior to the current storm, crampons and ice axes were helpful on steep, hard, and icy surfaces; and where snow remained, southerly surfaces developed a mature melt/freeze crust. Many above treeline slopes were wind scoured and rock strewn prior to the current storm.
Below Treeline (~below 10,800')Steep northerly, northeasterly and easterly slopes near and between 10,400' and 11,500' may have a persistent slab problem. See previous comments in the near and above treeline section.
New snow will hide rocks and logs on southern and western aspects. For telemark skiing, alpine touring, and splitboarding, northern aspects should have acceptable coverage down to ~8,500 feet, possibly a bit lower.
Northly, northeasterly and easterly slopes between 10,400' and 11,500' may harbor persistent slab problems, where new snow was deposited over mid-February snow and near surface facets. See image below.
There may also be a crust associated with this persistent problem (see snowpit below).
Mid-February snow overlaying weak near surface facets on Doyle Peak. February 21, 2022 photo by Troy Marino.
Always carry the 10 essentials and avalanche rescue gear for wintertime wilderness travel. Submit your observations here.
For AZ Snowbowl uphill access updates please refer to snowbowl.ski and flagstaffuphill.com. The Kachina Peaks wilderness is accessible from the lower parking lots at Snowbowl.
Updated Friday February 25
28" of new snow accumulated at 10,800' between Feb 22-24. Snowslide Canyon reported ~1.8" of snow water equivalent. Arizona Snowbowl Ski Patrol observed snow transported by southwesterly winds on Wednesday, February 23, then northeasterly winds on the February 24.
Overnight temperatures have been bitterly cold and will continue the next few days. "A tranquil weather pattern sets up across Arizona for the weekend and into most of next week resulting in mostly clear skies, periods of breezy northeast winds, and a slow warming trend... High pressure is forecast to take over by Sunday and through the middle of next week. High temperatures should gradually increase above normal Monday through Wednesday." - NWS Flagstaff
Snowslide SNOTEL reports 50" (127 cm) of snow at 9,730' on Friday, February 25. So far this winter, we have had a total of 119” (302 cm) of snowfall at 10,800' with a 67" (170 cm) undisturbed settled base depth reported by Arizona Snowbowl on February 25.
Since February 18, Snowslide SNOTEL low temperatures have ranged between 6°F on February 24 and 23°F on February 21, while highs have ranged from 21°F on February 23 to 46° F on February 19. For the same time period, ASBTP station (11,555') reports a low of -2°F on February 24 and a high of 39°F on February 19.
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.