This summary is generously sponsored by Peace Surplus. Voted best outdoor shop 10 years straight, by the people of Flagstaff and the Arizona Daily Sun.
Since last week, about 15" of low density snow accumulated on the San Francisco Peaks near 11,000 feet. Most of that came during the Valentines Storm, February 14th. Strong northerly winds blew all week. Much of the blowing snow was sublimated to the atmosphere, rather than redeposited - only small wind slabs with little reactivity were observed. Many slopes above treeline were scoured.
Due to warming temps, winds and persistent near surface facets, human triggered avalanches will be possible the next few days.
No natural avalanches reported this season, no human triggered avalanches reported since January 25, 2021.
Avalanche fatalities continue to add up for the western USA. For more information click read more below.
Between January 30 and February 18, 22 avalanche fatalities occurred in the U.S.
Could pandemic mindset be playing a role? The combination of pent up energy, reward seeking, and avoiding crowded ski areas after prolonged confinement may be clouding good judgment. Let’s not add AZ to the list.
Near and Above TreelineCoverage is variable and many westerly and southerly slopes are scoured to rocks. Many easterly aspects above treeline have decent to good coverage. Crampons have been helpful in areas of hard icy snow and wind packed snow
As warm springtime conditions start to appear, even dry slabs soften and become more susceptible to human triggers as they gain heat during warm afternoons.
Below TreelineWatch for very warm temperatures below treeline this week. Stay away from steep sunny slopes near terrain traps.
Below treeline, the snowpack is becoming thin and obstacle strewn. Northerly and easterly slopes have the best coverage, but finding sufficient snow cover for reasonable skiing on other aspects is becoming difficult below 10,500 feet.
Above freezing temperature are forecasted for treeline today and Saturday, then next Tuesday the mercury pushes 40°F near 11,500 feet. This rapid warmup may saturate the new Valentines snow, potentially creating loose wet avalanches.
With wind in the forecast and powder snow available for transport, new wind slab formation will be possible. If the 5 day forecast becomes reality, then wind slab issues will diminish as the melt/freeze cycle dominates.
Above treeline on an easterly slope, a reactive facet layer was observed about 12" down, under new valentines snow - see snowpit data below. This layer was not locally continuous, but may be more continuous on other easterly and northerly slopes near and above treeline.
With a lack of data from other easterly and northerly slopes, it is difficult to predict the probability of this problem. Backcountry travelers are encouraged to make their own slope specific assessments.
Snowpit data from easterly aspect at 11, 700 feet. February 18, 2021
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. Expect uphill closures during and shortly after large storm events.
Thank you to our generous sponsors for supporting the Kachina Peaks Avalanche Center!
Weather updated Thursday February 18
Since last week ~15" of low density snow accumulated on the San Francisco Peaks near 11,000 feet. Most of that came during the Valentines Storm, February 14th. Strong northerly winds blew all week. This week will consist of a warming trend interrupted by a couple of troughs, which will briefly drop the temperatures and create breezy conditions.
Snowslide SNOTEL reports 39" (99 cm) of snow at 9,730' on Thursday, February 18 down from a maximum of 51" (130 cm) on January 29th. Since Friday, February 12 Snowslide SNOTEL low temperatures have ranged between 6°F on February 17, to 20°F on February 12, while highs have ranged from 25°F on February 17 to 38°F on February 12. For the same period, ASBTP (11,555') reported a minimum of 1°F on February 17 /18, and a maximum temperature of 28°F on February12.
So far this winter we have had a total of 127" (323cm) of snowfall at 10,800 feet, with a 44" (112 cm) undisturbed settled base depth reported by Arizona Snowbowl on February 18.
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.