A potent fast-moving storm on March 22/23 dropped 17” of low density snow at 10,800 feet. Strong post frontal winds out of the northeast redistributed much of this onto leeward south and southwest facing slopes creating potentially dangerous wind slabs. Additional snow and strong southwest wind on Thursday transported available snow onto north and northwest aspects. Current wind direction is west, northwest at 11,500' and forecast to remain north over the weekend. Active precipitation for the next 12 hours and wind transport may further destabilize the snowpack.
Arizona Snowbowl reported 6" of new snow on Friday morning March 26, with an additional 6-10” in the forecast. For 24-48 hours after the current storm abates, natural and human triggered avalanches will be possible. Most hazardous terrain will be near and above treeline, leeward of prevailing winds, and cross-loaded terrain along the leeward flanks of gullies.
Warming temperatures, predicted on Sunday and Monday, may increase wind slab sensitivity and/or result in wet loose avalanches on sun exposed slopes. Wet loose avalanches typically start near heat absorbing exposed rock outcrops, and can potentially load and trigger cold slab avalanches on the slopes below.
Near and Above TreelineStrong NE winds on March 23, and southwest wind on March 24 have moved significant amounts of new snow, creating wind slabs on leeward aspects above treeline and along the flanks of gullies.
Prior to the recent storms, warming temperatures created a melt/freeze surface on many aspects above treeline. Before recent snowfall, steep sheltered, and shady northerly slopes still had powder snow. Bonding of new snow to the old snowpack surface will be highly variable based on the character of the snowpack below.
Stability tests have indicated some reactivity between the wind slab formed on Wednesday, and the new storm snow.
Crampons and ice axe may be helpful on slopes where the wind has removed soft snow, exposing hard/icy snowpack.
Below TreelineRecent snowfall has improved coverage, and some of the best riding conditions this winter have been reported. That being said, hidden obstacles still linger right below the enticing surface fluff.
Fresh snow rests on a springtime snowpack. A typical springtime melt/freeze cycle has dominated at lower elevations where the snowpack is becoming more uniform in temperature gradient (isothermal), and avalanche concerns are either related to melting (wet slides), or to poor bonding between new snow and old snowpack.
With the new snow, approaches and egresses have improved, but the warm temperatures in the next few days will quickly melt the coverage at lower elevations and sunny aspects.
Snow that fell last Tuesday was redistributed by strong NE winds on Wednesday morning. With more snow and winds in the forecast, the building of new wind slabs is likely.
Dangerous wind slabs may have been deposited on south and southwest aspects earlier in the week, but also, on northeast and north aspects from ongoing storm winds out of the southwest.
Backcountry skiers and boarders are advised to avoid travel on pillowed or hollow-feeling compacted snow near and above treeline. Dangerous wind slab conditions can be hard to accurately assess. Stability tests can yield misleading results since slab strength/thickness can vary dramatically over a small area, making identifying sensitive triggers points impossible.
Current forecast indicates breezy and stormy weather, so this problem is unlikely in the short term. But when sunny, spring weather returns on Sunday and Monday, watch for warming temperatures in the 40s F creating wet saturated slopes. These will be most evident near exposed rocky outcrops on sun baked slopes.
Evidence of old avalanche debris in the runout of Telescope Path, north face of Doyle Peak, 10600 feet. Photo taken on 3/25 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. 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 March 26
A surprisingly productive storm impacted San Francisco Peaks on Tuesday March 23 dropping 17” of low density snow at 10,800 feet. Snowslide SNOTEL station reported 11” of new snow and 1.3” of SWE. This was followed by very strong NE winds, gusting to 50+ mph on Wednesday morning. Snow that didn’t return to the atmosphere was loaded onto leeward slopes and cross-loaded in gullies.
Another less vigorous storm is now in the mix, predicted to lay down another 6-12” by its culmination on Friday night. High velocity SW winds will accompany this storm. Sunny skies will follow starting Saturday with a distinct warming trend. Treeline temperatures are expected to rise into the upper 40s on Monday March 29. Breezy winds, typical of spring in Arizona, will be present as a low pressure system passes to our north mid-week.
Snowslide SNOTEL reports 53" (135 cm) of snow at 9,730' on Friday, March 26, down from a maximum of 59" (150 cm) on March 14. So far this winter, we have had a total of 210" (518 cm) of snowfall at 10,800 feet; with a 71” (173 cm) undisturbed settled base depth reported by Arizona Snowbowl on March 26.
Since Friday, March 19 Snowslide SNOTEL low temperatures have ranged between 14°F on March 22 and 31°F on March 20, while highs have ranged from 29°F on March 25 to 54°F on March 19. For the same time period, ASTP station (11,555’) reports a low of 3°F on March 22 and a high of 45°F on March 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.
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.