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Holiday cheer is being delivered to the San Francisco Peaks in the form of snow! While coverage pre-storm has been thin, with a 16" base at 10,800', the current winter weather system could deliver the needed snow to open the backcountry for the season.
This storm will likely provide the base for future backcountry winter travel, and a longwave weather pattern should deliver continued accumulation throughout the week. Continued 30 + mph southwest wind will create wind slabs on leeward terrain.
Although this system is delivering heavy snow, be aware that the snowpack will be unsettled in the short-term, and that current new snow accumulations, while they may look impressive, expose equipment and travelers to below surface hazards.
In general, avalanches are possible on wind loaded slopes, and especially likely above treeline; and will remain possible on all slopes with enough storm snow and continued wind transport. Southwest winds of 30 + mph are forecasted in the upcoming few days making wind slab avalanche hazard a possibility on leeward slopes. Cross-loading is also likely, thus further complicating above tree line travel. Do not underestimate storm conditions on the San Francisco peaks and general travel hazards due to cold, wind, poor visibility and snow accumulation.
Prior to the storm there was about 4 to 6" of snow on northerly slopes at 8,200 feet. Current base depth at 10,800' is 33" with approximately 20" being reported as delivered in the last 24 hours, as of early afternoon. Much of the existing pre-storm snowpack is comprised of facets and has not been supportable of backcountry travel. Additional accumulation will improve these conditions, but backcountry travelers should be extremely cautious. Wind slabs may prove dense and heavy enough to fracture and slide on the weak faceted base. Be aware of hollow sounding slabs, shooting cracks and 'whoomping', all red flag signs indicative of an unstable snow pack.
If you haven't already done so, take the time to prepare your ski/ride equipment and kit; check your beacon and practice your rescue skills. The backcountry will hopefully open soon.
Near and Above TreelineExpect improved coverage since the last storm, but the snow from this storm will likely be unconsolidated, making log and rock hazards a continued issue. The best coverage appears to be on some easterly and northeasterly slopes. Even if high elevation slopes with sufficient coverage exist, obvious and hidden obstacles will make the approach and egress hazardous.
Wind slab avalanches may be possible. Lower elevation terrain traps should be evaluated carefully, as there is enough wind activity at all elevations to crossload terrain features.
Below TreelineLower elevations have received mostly rain during the ongoing storm. The current snow level is expected to drop. Backcountry travelers brave enough to venture out should note that a change in conditions may make it possible to trigger small avalanches on windloaded slopes above 10,000 feet. Below this elevation, avalanches are unlikely. When venturing into the backcountry, keep in mind the increased consequences of being involved in a slide due to the thin coverage.
Congratulations to our raffle winners James Brooks and Cole Kaplan for winning the Level 1 Avalanche course raffle and power pass raffle, respectively. Thank you to all the great supporters who purchased tickets to help with continued avalanche education!
For AZ Snowbowl access updates please refer to snowbowl.ski and flagstaffuphill.com. Uphill travel within the Snowbowl ski area boundary is currently closed. The Kachina Peaks wilderness is accessible from the lower parking lots at Snowbowl.
Always carry the 10 essentials and avalanche rescue gear for wintertime wilderness travel. Submit your observations here.
Updated Friday December 24
Cool temperatures over last weekend were followed by stable weather, mild temperatures, partly to cloudy skies and light winds. A significant pattern change was introduced on Thursday with a long wave trough dominating the western United States.
This pattern is predicted to stay in place for a number of days as it functions as a conveyor belt, transporting several short wave disturbances across the region. Since moisture carried by these storms was drawn in from the tropics, temperatures are on the warm side, causing the freeze line to be initially elevated to 8500-9000 feet, but then dropping to 6800 to 7000 feet.
By early next week, this series of storms could deliver 20-30” of high density snow accumulation at 10,800 feet. Lower elevations are likely to receive a “wintery mix” of rain, snow and sleet. Winds will be south to southwesterly with sustained velocities in the upper 20s and ridge top winds gusting to 40 + mph. Keep in mind the anemometers' used to monitor wind at upper elevations tend to freeze up with rime and under report the actual wind speed, or report zero.
This longwave pattern may remain in place through the week, potentially introducing more unsettled weather during the days leading up to New Year’s weekend. It looks like the holiday gift train is coming through.
Snowslide SNOTEL reports 9" (23 cm) of snow at 9,730' on Friday, December 24. So far this winter, we have had a total of 37" (94 cm) of snowfall at 10,800' with a 33" (84 cm) undisturbed settled base depth reported by Arizona Snowbowl on December 24.
Since December 17, Snowslide SNOTEL low temperatures have ranged between 8°F on December 18 and 35°F on December 22, while highs have ranged from 31°F on December 18 to 45°F on December 22 For the same time period, ASTP station (11,555') reports a low of 18°F on December 18 and a high of 41°F on December 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 email@example.com.