Rapid arrival of above average springtime temperatures is raising concerns regarding wet avalanches conditions. Wet loose avalanches will be likely over the weekend and into next week. These will be mainly relatively benign loose wet avalanches on sun exposed aspects, both above and below treeline, and primarily on southern aspects. Such events are expected to be prolific, but relatively small in size.
Also possible, but less likely, are larger and more dangerous wet slab avalanches. These are sometimes triggered by percolating melt-water in the snowpack that encounter impermeable ice crusts; such circumstances can create a destabilizing weak layer releasing a cohesive wet slab above.
Intermittent breezy afternoons in the forecast will partly abate the rate of melting, contributing to stability. However, if nighttime temperatures are near or above freezing, and afternoons are extra warm and windless, instability can rise remarkably fast. With a dramatic warming trend in the forecast for Easter and continuing into the workweek wet avalanches will be possible.
Near and Above TreelineOver the last week, warming temperatures stabilized the snowpack and created some new melt/freeze surfaces on many aspects above treeline. Steep, sheltered, and shady northern slopes may still retain some powder snow, despite the heat wave last week. Presumably, sufficient bonding has occurred between our last snow storm and the snowpack below for good stability. Recent tests have indicated low reactivity between the wind slab formed on Wednesday March 24 and the storm snow on top.
Crampons and ice axes may be helpful on slopes where the wind has removed soft snow, exposing hard/icy snowpack. In the mornings, icy southern exposures can be anticipated before warming temperatures soften the surface.
Excessive melting resulting in sloppy saturated snow will be the primary concern during the week ahead. If sloppy snow becomes difficult to deal with, get off and onto cooler more northerly aspects, or onto a ridgeline free of snow.
Below TreelineSpring/summer conditions have abruptly arrived at lower elevations. Previously hidden obstacles are quickly revealing their ugly heads.
What was fresh snow last week has rapidly become a springtime snowpack characterized by melt/freeze metamorphism. A uniform temperature gradient (isothermal snowpack) is now the dominant condition at lower elevations effectively shutting down facet development as a weak layer forming mechanism. Avalanche concerns are now either loss of strength due to melting (wet slides) or to poor bonding between the new snow and old.
Loose wet avalanches will continue to be a concern with well above average temperatures in the forecast for Easter Sunday and the following days. Be careful when traveling above dangerous terrain traps. Even an otherwise minor slough could carry a skier or boarder over a cliff, into unforgiving trees or bury him/her in a confined gully. Loose wet avalanches have been known to load and trigger larger more dangerous wet slab avalanches.
With warm nights and daytime high temperatures predicted to be 15-20 F above average on Sunday, Monday and later in the week, the possibility of wet slab avalanches can not be ruled out.
Wet avalanches are commonly natural occurrences, rather than triggered by the weight of a skier or boarder. The key is moving off wet, melt-water saturated slopes, and onto cooler aspects as the day progresses.
Be aware of the role played by elevation, keeping in mind that lower elevations heat up before higher elevations. This factor needs consideration in planning exit routes later in the day. A key to safely recreating in the springtime is early starts and short days, return to safety of the trailhead before the heat of the day.
Rapid and continuous melting can result in dangerous wet slab avalanches. In the springtime snow scientists use the first three consecutive days when mean temperatures are above freezing as a red flag marker for increasing wet slab instability. Such temperatures and rapid melting are possible near treeline during the upcoming week.
During ski cutting mitigation operations, Snowbowl Ski Patrol triggered a medium sized wind slab avalanche on 3/27 in the Shiprock Chutes (HS, AS, R2.5, D2). Photo by Tanner Porter.
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 Friday April 2
Warm springtime conditions characterized most of last week. Breezy afternoons held excessive heat at bay, and nighttime cooling kept the corn-making freeze/thaw cycle alive.
The weekend will start with some potential convection cloud build up, and possibly even some graupel showers, or lightning. Unsettled weather will be short-lived as high pressure ridging takes hold on Easter Day. On Sunday and Monday high temperatures are expected to be 10-15°F above average, rising into the mid 50s at treeline. Nighttime lows will hover around the freezing point.
The rest of the workweek remains uncertain. A deep digging low will either impact us with unsettled weather or fall apart before it gets here. Either way, little or no accumulation of snow is expected.
Snowslide SNOTEL reports 39" (99 cm) of snow at 9,730' on Friday, April 2 down from a maximum of 59" (150 cm) on March 14. So far this winter, we have had a total of 216" (548 cm) of snowfall at 10,800’ with a 59” (150 cm) undisturbed settled base depth reported by Arizona Snowbowl on April 2.
Since Friday, March 26 Snowslide SNOTEL low temperatures have ranged between 11°F on March 31 and 35°F on March 29, while highs have ranged from 33°F on March 26 to 56°F on March 28. For the same time period, ASTP station (11,555’) reports a low of 13°F on March 27 and a high of 51°F on April 1.
Despite drought conditions during autumn, December and February, the saving grace of Miracle March brought Flagstaff up to ~95% of average annual snowfall for this time of year.
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.