Avalanche conditions continue to moderate. Snowpack structure on the most avalanche prone slopes is poor to moderate; snowpack strength is moderate to high, and propagation potential is moderate to low. Additional precipitation and westerly winds forecast for Sunday, February 26, may transport enough snow to produce wind slabs and unstable conditions.
The President's Day weekend storm laid down 12-14 inches of fairly high density new snow. As a result, on February 19th seasonal snowfall this year exceeded the winter average of 260 inches at Snowbowl mid mountain (10,800').
On President's Day, February 20, skiers in the Inner Basin observed small and medium sized avalanches in the vicintiy of Humphrey's Cirque. These most likely released naturally during the storm cycle on Saturday or Sunday; new snow sliding on the old snow underneath or on near surface facets within the upper 20-30 cm of the pre-storm snowpack. Avalanche control work at the Arizona Snowbowl on the same day released shallow wind slabs on northwest aspects.
Strong winds on Wednesday from the west may have transported and loaded storm snow from President's Day weekend onto east facing leeward slopes and cross-loaded gullies.
Storm snow has stabilized, however wind slab deposited on Wednesday may remain sensitive and prone to skier triggering. Although a new storm is forecast to arrive on Sunday is not expected to produce significant precipitation. If forecasted precipitation is exceeded, avalanche hazards will rise.
The President's Day storm was followed by warming conditions on Monday and Tuesday. On Wednesday, strong winds out of the west were recorded as a cold front passed north of our region, ushering in cold and breezy conditions later in the week. On the horizon, a storm is forecasted to arrive by Sunday, however moisture is modest and heavy snowfall seems unlikely. If new snow exceeds forecasted amounts or is transported by wind, avalanche hazard will increase.
Near and Above TreelineThe forecast for Sunday, February 26, may produce a few inches of new snow at higher elevations, with wind from the west and southwest, thus loading the east and northeast aspects.
On thin northerly aspects, wind slabs may be resting on weak near surface facets that started developing during this weeks cold and clear evenings. The warm/cold imbalance has created a temperature gradient that encourages facet growth. Recent pit analysis reveals a lingering strong temperature gradient in the top 20 -30 cm of the snowpack. Facets will continue to develop 20 - 30 cm below the old snow surface, potentially creating a persistent weak layer upon which new storm and wind slab will rest.
Below TreelineSun and radiation affected slopes developed melt/freeze crusts, and continued cold temperatures this week are preserving these crusts and rigid snow surface on south facing terrain. A rain event on Tuesday brought a freezing surface layer up to 10,000' on the west side of the Peaks.
Shaded aspects continue to provide excellent skiing opportunities above 10,000'.
Coverage is great above 9000'. The warm temps have melted much of our snow below 8000', especially on sunny slopes.
New snow may create storm and wind slabs, especially above treeline. Even with light precipitation amounts, wind can deposit significant amounts of snow on leeward slopes, as well as cross load gullies and chutes. Wind slabs usually stabilize in less than a week. Reduce your exposure to avalanche hazard by waiting several days after a big loading event.
Always keep in mind, wind slabs are unpredictable, and may support the weight of a skier or rider initially, and fail suddenly with tragic consequences. Avoid snow surfaces which are recently loaded, sound hollow, have signs of fracturing, cracking, or whoompfing sounds.
If new snowfall reaches or exceeds maximum depths forecasted, storm slab and wind slab avalanches may become likely. The development of near surface facets at the boundary of new and old snow could turn a storm slab concern into a persistent slab problem.
Make objective observations of current and changing conditions, and incorporate these into your flexible plan. Forecast what may happen next. Photo by Nico Barraza.
This season numerous rescues have been conducted by Coconino County Search and Rescue, and the Arizona Snowbowl Ski Patrol. Some of these could have been avoided by better planning and preparation.
Travelers are advised to exercise caution, make slope specific evaluations and most of all, know where you are going and be prepared for the unexpected.
As always, please treat this summary with appropriately guarded skepticism, make your own assessments, and contribute to our body of knowledge by reporting your observations.
Want to learn more safe backcountry habits? KPAC offers level I and II avalanche courses. There is one class left this season.
During winter, backcountry permits are required to access the Kachina Peaks Wilderness. More info
Last updated on Friday, February 24, 2017.
Normal seasonal temperatures, and variable gusty winds out of the south-southwest and west followed the President’s Day weekend storm. Wind velocities exceeded 30 mph on Wednesday February 22nd and shifted to a northerly direction on Thursday and continued ever since. Cold temperatures and wind chill to -18° F was reported at the Agassiz Peak Station on Friday morning February 24th. Light precipitation will return to our region on Sunday, Monday and Tuesday accompanied by strong winds out of the west and southwest, as a series of short wave disturbances pass through. These appear to be lacking in moisture and are not expected to deliver more than a few inches of snow at higher elevations. Mostly clear skies and near normal temperatures will prevail for the rest of the week.
On the morning of Friday, February 24th the Inner Basin SNOTEL site (Snowslide) reported a snow depth of 76 inches (193 cm) at 9700’, and Arizona Snowbowl reported 92 inches (234 cm) at 10,800'. These values are expected somewhat to increase as precipitation starts to fall during the weekend and into next week. Since February 17th SNOTEL temperatures ranged between 13° and 47° F and Agassiz station between 0° and 34° F.
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.