What do you get when it snows, rains, and the sun comes out in a winter that had multiple, long, dry spells?

The answer: prolonged, very scary avalanche conditions for most of western Canada! That’s been the story of this week, with many very large avalanches failing deep within the snowpack in a huge avalanche cycle that peaked on Wednesday.

One of many recent very large persistent slab avalanches in the Sea to Sky region.

Now, we enter a period of uncertainty as we gingerly poke our heads out after watching the sky fall down. The buried weak layers that caused all the fuss are still there… Are they still a problem? Will a crust thicken above them that prevents triggering? Will it stay cloudy and stormy, preventing a thick crust? Is the new snow that is starting to fall going to continue overloading the buried weak layers?

The fine details will really matter when answering these questions—so now more than ever, tune into your local forecast before heading out to see if and when avalanche conditions will improve. 

A large avalanche failing on a deep weak layer in the South Rockies. Credit: AvCan South Rockies Field Team MIN

A very large avalanche north of Revelstoke stepped down to deeply buried weak layers in the snowpack and propagated widely.

If you head into the mountains over the next few days, you’ll see some very large avalanches from this week. Take the opportunity to reflect on where you travel in the mountains and interact with avalanche terrain. 

Have you ever seen avalanches run this far? Did they wipe out your prime weenie roast or charcuterski spot? 

Could travelling 100 feet to the left or right have made a difference if you were there during the avalanche?

Have you been in avalanche terrain without even knowing it?

A large avalanche buried the Duffey Lake Road on Tuesday evening. Source: x.com

Now is a good time to pause and reflect on past decisions, so we can continue to improve our decision-making in this wicked learning environment. In the short term, there is a lot of uncertainty about how conditions will play out. So, focus on what you can control, which is the terrain you choose. Gather information and gain confidence in your local conditions on small slopes that are free from terrain traps, and the odds are in your favour.

Avalanche in the Selkirks, credit @powder.cowboy on Instagram

Video of an avalanche hitting a lake in the Selkirks, shared on Instagram by @powder.cowboy. Warning: language.

Avalanches were running far into the runout zones. This is a good reminder that just because there are spring conditions in the valley, overhead avalanche danger can still exist. Credit: BC-MoTT / Bear Pass-Stewart Avalanche program – Automated Avalanche Detection System

Another very large avalanche in the Purcells hit a lake and sent water flowing down the slope below.

Cool... but not chill

It’s no secret that spring can offer some of the most enjoyable conditions in the mountains. Warmer and longer days make it prime time for adventures, but the season also comes with unique avalanche hazards to keep in mind.

Early spring has historically been one of the deadliest times for avalanches—likely due to a combination of rapidly changing weather, persistent weak layers, and human factors. When we add long, sunny days that can create a false sense of security into the mix, it can be a recipe for underestimating avalanche risk. 

Preparing for a wide range of conditions is key. It might feel like summer in the valley while winter lingers at higher elevations, or warm temperatures may reach the mountaintop. Understanding the avalanche forecast and mountain weather can make all the difference in keeping your spring adventures safe and enjoyable.

Very large avalanches on deeply buried weak layers should be expected, like this recent example from the Valemount area. Credit: Boosted Imagery

A significant warming event will bring a serious rise in avalanche danger this week and shift us into more spring-like conditions. Freezing levels are forecast to rise towards 3000 m, impacting the South Coast on Tuesday, and seeping into the southern interior Wednesday.

Large and destructive avalanches are a major concern as persistent weak layers across many forecast regions are expected to become reactive. In shallow snowpack areas, such as the eastern Purcells and Central Rockies, weak snow at the base of the snowpack may produce full-depth avalanches.

This will be an extra layer of complexity to manage alongside our usual spring concerns. 

By Wednesday afternoon, freezing levels are forecast to reach over 3000 m in many regions. Source: Mountain Weather Forecast

Typical Spring Avalanche Hazards and Problems to Watch Out For

Sunshine and warm temperatures weaken the snowpack, reducing cohesion and increasing the likelihood of avalanches. 

Morning sun impacts east-facing slopes, shifting to south and west aspects in the afternoon, with the strongest warming near rocky outcrops. 

Snow that doesn’t refreeze overnight deteriorates faster as daytime temperatures rise.

Rain-on-snow events rapidly destabilize the snowpack.

A widespread avalanche cycle should be expected during the upcoming warming, like this example from the start of March. Credit: South Rockies Field Team

Rapid warming can trigger buried weak layers.

Dormant weak layers from January and February may become active again. These layers are widespread across many forecast regions.

Large avalanches may run to valley bottom—often into terrain where recreationists would not expect overhead danger. 

The risk is especially high during the first major warm-up of the season.

Wet avalanches have the potential to run long distances in the spring. This example from the Fernie area is a good reminder that avalanches can run through forests and that knowing what is above you is always important. Credit: South Rockies Field Team MIN.

Sun and warm temperatures weaken these overhanging masses of snow. 

Cornices can break suddenly, posing a serious hazard for anyone on the ridge or the slope below.

Cornice falls are large loads that have the potential to trigger deeply buried weak layers, producing very large avalanches.

Large overhanging cornices like this near Whistler are a major concern as we head into spring. Give these a wide berth when traveling on ridges and minimize your exposure to overhead slopes with cornices, especially during periods of warming and sun. Credit: MIN User Kirill Kokorin

Instabilities often linger on high-elevation, north-facing slopes, where they are last to be affected by spring warming and protected from the sun.

Convective flurries are short-lived, localized weather events that can deliver sudden bursts of heavy snow, reduced visibility, and gusty winds. They can elevate avalanche danger by rapidly forming storm or wind slabs.

Widespread storm slab avalanche activity was observed over the weekend. The recent storm snow is expected to remain unstable as the warming progresses. Credit: MIN User BARKER.DBEN.

Remember, avalanche risk isn't the only concern in spring. Warm days and cold nights drive melt-freeze cycles in the snowpack. Hard surface crusts are often present in the morning, reducing avalanche danger but making self-arrest difficult on steep slopes.

With thoughtful planning and decision-making, you can still enjoy the best of spring.

Check your local avalanche forecast and avoid exposure to avalanche terrain during high danger.

Remember snowpack and avalanche problems will vary significantly with elevation.

Conditions can deteriorate rapidly. Be prepared to step back to simple terrain and avoid overhead hazards to minimize your exposure.

If traveling on exposed slopes, do so early in the day before warming and sun weakens snow surfaces and cornices.

Stay ahead of conditions by being flexible with your plans, and prioritizing safety as we enter this significant warm-up and the mixed bag of spring conditions that will surely follow.

From Storms to Spring

The Canadian Rockies had a significant storm around the weekend of March 9, delivering up to 80 cm of new snow across the region. All this new snow landed on a weak underlying snowpack, consisting mostly of faceted snow crystals–loose, sugary grains that offer little strength or cohesion. As a result, the new snow is resting on what is essentially layers of ball bearings.  

During the storm, the region underwent a major avalanche cycle, with many large avalanches up to size 3.5. While the rate of natural avalanche activity has declined since the storm, large avalanches continue to occur daily in the Rockies. These avalanches are likely being triggered by intense solar radiation and significant temperature fluctuations throughout the day. 

Don’t view a decreased frequency of natural avalanches as a sign of declining risk–the snowpack remains highly susceptible to human-triggered avalanches. This week, there have been numerous reports of people remotely triggering avalanches or experiencing close calls. 

A skier remote triggered a size 2 avalanche from 24 degree terrain, which resulted in six additional sympathetic persistent and deep persistent slab releases. Four were size 2-2.5, and two were size 3-3.5. Credit: MIN User chrisgranter 

Tragically, two people died in the Rockies this past week–both fatalities occurred on the same day in steep, treed terrain. Photos from the incidents show fairly dense tree cover, which can give a false sense of security and may lead us to let our guard down. These tragic incidents underscore the need for caution, even in areas where we may not expect avalanches. 

Small to medium sized trees in the start zone and track of a fatal avalanche on March 14. Credit: BNP Visitor Safety. Read the Fatal Avalanche Incident Report

Image of avalanche path taken from rescue helicopter after fatal avalanche on March 14. The lower red outline indicates the avalanche the skier was caught in, and the smaller outline indicates a sympathetic avalanche. Credit: Kananaskis Mountain Rescue. Read the Fatal Avalanche Incident Report

While it may be tempting to over-analyze the various layers within the snowpack right now in search of safety, the key takeaway here is simple: don’t try to out think this snowpack. The safest course of action is to avoid all avalanche terrain of consequence, including terrain traps and runouts.

Another 10-15 cm of snow forecast before the weekend, which may lead to favourable skiing conditions. However, the underlying instability in the snowpack will still pose significant risks. Stick to low-angle glades and avoid any terrain that exposes you to avalanche paths. Persistent weak layers are especially dangerous because they can lead to large, unpredictable avalanches, may be triggered from a distance, may cause sympathetic avalanches, and may propagate widely.

Banff Parks Mountain Safety staff observed this avalanche on a rescue flight. It propagated for 2.4 km! It likely initiated on a persistent weak layer and stepped down to the deep persistent layer at the ground in some places. Credit: Parks Mountain Safety

This is not a short-term issue. The weak layers buried deep in the snowpack are not expected to heal quickly and will continue to pose a problem for a while, requiring sustained caution. We use the word “persistent slab” in the avalanche problems section of the forecast because that’s what it is–an instability for an extended period of time.

Ice climbers should also assess their surroundings carefully. Be mindful of terrain you might normally consider benign—does the steep, treed slope above you have the potential to avalanche?

The snowpack in the central Rockies remains complex, and continues to demand caution, conservative decision-making, and careful terrain choices. In these conditions, even small missteps can have serious consequences. Before heading into the mountains, always check the latest avalanche forecast at avalanche.ca and ensure you are carrying—and know how to use—the essential gear: transceiver, probe and shovel. The mountains aren’t going anywhere—make choices that ensure you can return to enjoy them another day.

People starting to step out into serious avalanche terrain at Parker Ridge. Numerous avalanches up to size 3.5 occurred across the valley in previous days. Credit: Jasper National Park Visitor Safety

A size 3.5 natural avalanche this week at Assiniboine Lodge. Credit: Claude Duchesne

Jasper National Park Visitor Safety was called out when a large powder cloud was observed coming off Mount Kitchener while multiple snowshoeing groups were in the area. No one was involved. Credit: Terry Larson

The key takeaway here is simple: don’t try to out think this Rockies snowpack. Avoid consequential avalanche terrain. 

High Alert in the Canadian Rockies

Winter isn’t over yet. Most of our regions saw significant snowfall last weekend, with an average of 50 cm in 48 hours for the interior and over 1 meter for the south coast. After those storms, the taps stayed on with another 20 to 40 cm arriving mid week. Both of these systems came in warm, with strong southerly winds, and the result was some impressive, widespread avalanche activity.

Natural storm slab avalanche activity was widespread last weekend. Credit: VARDA

For most regions, we will see a break in the weather for Friday, but active weather is coming in right behind it for western Canada—although we are uncertain about the timing and intensity of this storm. This will mean there is all the more reason to keep an eye on our forecasts and be sure to double check again in the morning before heading into the mountains. In times of uncertainty, we may make last minute updates with the most current information available.

Precipitation forecast for Thursday afternoon through Sunday afternoon shows substantial amounts for the coastal regions and the southern interior. Source: Environment Canada

As well as the storm and wind slab problems caused by the recent snow, we also have concerns about the snowpack structure. The layer that’s on our minds most at the moment is the early-March crust/surface hoar layer. This layer is found around 50 to 70 cm deep in most regions in western Canada, but over 1 meter on the south coast and parts of the Selkirks. This means it has the potential for producing very large avalanches and it has already been responsible for many avalanches up to size 3.5. We suspect this layer will remain a concern for the near future, especially in the interior.

With a variety of weak layers in the snowpack, remotely triggered avalanches remain possible like this one that was triggered from 200 m away in the White Pass area last Sunday. Credit: MIN User karla

The recent storm snow has a poor bond to the old snow surface in many areas. Storm slabs remain a major concern for human triggering in many regions. Credit: North Rockies Field Team MIN

In regions with a shallower snowpack, such as in the East Purcells, Rockies, and inland side of the northwest coast, we still have concerns with weak layers from mid-February and late-January. Despite these regions potentially seeing less active weather this weekend, strong solar input could be a driver of hazard and may wake these layers up.

Old weak layers from January and February remain reactive in some areas. Credit: South Rockies Field Team MIN

Spring can be a challenging time due to the mixed bag of conditions you may find in the mountains. The weather is dynamic and less predictable, making it more difficult to forecast and potentially highly variable throughout the day. More than ever, you need to keep your head up and verify conditions as you move through terrain. Hazard can change quickly, even from aspect to aspect and hour to hour.

Get the forecast so you can know more, go further, and take advantage of all the deep pow out there more safely.


Winter Isn't Over Yet

We currently have a Special Public Avalanche Warning in place for most of our forecast regions in western Canada due to a tricky snowpack and challenging persistent slab problem. As we head into the weekend, the warm and sunny weather forecast is likely to exacerbate this problem. 

There has been a worrying trend with many of the avalanches we’ve seen reported over the last few days: wide propagation and remote triggers. These characteristics add an extra layer of complexity to an already difficult problem. 

An avalanche near Kootenay Pass on Monday propagated widely across multiple features. 

Wide propagation and remote triggering are both indications of a prominent weak layer in the snowpack with a cohesive slab above it. When an avalanche can propagate widely, it can run across multiple features in a slope, even if they appear somewhat disconnected. This means the avalanche can be much larger than expected and run much further than normal. 

This natural avalanche near Pemberton on Wednesday propagated 600 m wide across multiple features on the slope. 

To add to this concern, we also have plenty of reports of remote triggering, where the avalanche occurs away from the point where it’s triggered. They can be triggered from a fair distance away from the avalanche path, including from ridgelines above, on an adjacent slope, or from flat terrain below. Predicting where or when you might remotely trigger an avalanche is almost impossible.

This avalanche was triggered remotely from 75 m away on low-angle terrain.

This slope near Lake Louise was remotely triggered by skiers travelling on the shoulder above it. Credit: MIN user col.j.stew

All of this means that we need to take a different approach to travelling in the mountains this weekend. Areas that normally seem safe may be dangerous, and there may be no warning signs that instability is present. The only way to manage the risk is through managing your terrain choices and practising good travel habits. 

Always be aware of your surroundings and watch what is above you; it is possible to trigger avalanches from the bottom of an avalanche path. 

Watch for other groups and give each other a wide margin of error. Remember, remote triggering is possible from a distance.

Avoid exposure to overhead hazards, especially during periods of strong sun and warming. 

Choose really good safe spots. Like really good. Persistent slabs will propagate much wider than you might expect and pull back into surprisingly low-angled terrain. Make sure you are regrouping well away from danger.

Maintain good communication. Radios are a useful tool within your group. Make sure everyone is on the same page. “Where are our safe spots?” “What is the escape route if an avalanche does happen?”

And of course, use terrain wisely…when the snowpack is the question, terrain is the answer!

Make your uptracks in the safest place you can. Think ridges, ribs, and forested areas.

Be diligent about terrain choices, and stick to slope angles less than 30 degrees when in clearings, open trees, and alpine terrain.

Be aware of what’s above and around you. Remote triggering is a real concern right now! Avoid terrain traps that could increase the consequences of an avalanche. 

The bottom line is that this is an avalanche problem that you really don’t want to gamble on. The consequences of an avalanche are incredibly high, and it’s just not worth the risk of sticking your neck out there. Dial it way back and reframe your goals from “shredding the sickest line we possibly can” to “having a fun day out riding with friends.” The mountains will always be there, and we want to make sure we’re there to enjoy them when they’re safer—it’s time to take your foot off the gas, slow it down, and get back to basics. 

This large avalanche near Whistler was remotely triggered from flat terrain over 100 m away and subsequently propagated 400 m wide across multiple features on the slope.  

Remote triggering small slopes from flat terrain is a clear indication to stay away from larger slopes where the consequences would be much higher. Credit: North Rockies Field Team MIN

This avalanche near Pemberton last weekend was remotely triggered from flat terrain 150 m away. Credit: MIN user matthew.dahabieh

Wide propagation and remote triggering have us worried

Remote Triggers, Wide Propagation and Why You Need to Dial It Back

Dangerous avalanche conditions exist in most regions in western Canada. A cohesive slab of 50 to 100 cm of snow overlies a weak upper section of the snowpack, consisting of various layers of surface hoar crystals, faceted grains, and hard melt-freeze crusts. This has created a reactive avalanche problem that resulted in many near-misses last weekend and unfortunately one fatality. We’ve seen widespread natural and human-triggered avalanche activity, with humans triggering large (size 2 to 3) avalanches on steep slopes or adjacent to them (remotely triggered).

This snowpack setup will be slow to strengthen and it may take weeks for the likelihood of triggering avalanches to decrease. It will be important to focus on maintaining good travel habits, as getting caught in one of these avalanches could be fatal.

Here are some risk management strategies to stay safe during this tricky period in the backcountry:

Adopt a conservative mindset when in avalanche terrain.

Be diligent about terrain choices, sticking to slope angles less than 30 degrees when in clearings, open trees, and alpine terrain.

Follow disciplined group decision making, ensuring that each group member is engaged in terrain selection.

Back off sun-exposed slopes if it is warm and sunny and expect natural avalanches during stormy conditions.

Minimize exposure to overhead hazard, given that these avalanches can be remotely triggered and travel into runout zones.

Travel one at a time when exposed to avalanche terrain and regroup in safe spots well away from overhead hazard.

Avoid exposure to terrain traps, such as gullies, cliffs, and trees to reduce the consequence of being caught in an avalanche.

Practice patience, avoid complacency, and accept that you may need to manage this risk for weeks to come.

Naturally triggered slab avalanches occurring on any steep terrain feature in this photo near Pine Pass in the North Rockies. (MIN user Dave)

A snowmobiler triggered a large avalanche that propagated widely in the South Rockies. (MIN user markusvandenhoek04)

A large slab avalanche near Whistler. (MIN user zachwass2000)

A remotely triggered avalanche near Duffey Lake Road in southwest BC. Skiers walking on the slope in the foreground of the picture triggered a buried weak layer that propagated over to the steep slope, causing it to avalanche. (MIN user Matthew Dahabieh)

Lingering Danger

Dangerous avalanche conditions are expected to return to parts of Western Canada as a series of storms brings mild temperatures, heavy snowfall, and strong winds. The incoming snow will bury a weak upper snowpack which developed during the periods of extended cold and dry conditions through January and February, setting us up for a period of instability. Because the exact timing, intensity, and track of each storm system remain uncertain, it will be important to regularly check the avalanche bulletin heading through the weekend. One thing is certain, it’s time to dial back our exposure to avalanche terrain.

An avalanche that failed on the late January weak layer near Fernie recently. New snow and warming are expected to increase the likelihood and size of avalanches failing on this weak layer. Source: MIN user SAMIRSOMJI

Extended periods of cold and dry conditions through January and February brought stable avalanche conditions and relatively low avalanche danger to much of southern BC and Alberta, but they also caused the formation of weak layers of surface hoar, facets, and/or crusts in the upper snowpack. There are currently at least two major weak layers that we’re expecting to become reactive as this series of storms arrives.

Depending on your location, you likely saw one or more weak layers form during January’s dry spells, which were then buried by a big storm at the start of February. Although the storm brought up to 80 cm of new snow to the south coast and 40 cm to the southern interior, heightened avalanche danger was short-lived. This is because the weather returned to cold and dry, preventing the new snow from settling into a widespread slab over that weak layer. We did see lots of natural avalanche activity in specific areas where the wind formed cohesive wind slabs, as well as numerous human-triggered avalanches failing on this layer, but avalanches generally remained on the smaller side. The storm snow simply lacked the cohesion and slab properties that would allow for wide propagations and widespread large avalanches. Crisis averted–but not indefinitely.

The cold and dry February conditions compounded this situation and added a second weak layer of note, formed in much the same way as the first.

(Psst—want to know more about what makes a cohesive slab? We have a blog about that! What Is a Slab? Forecaster Blog)

The weak layer from late January is a prominent feature in the snowpack throughout southern BC. Credit: MIN User ALPINELIFESNOWPACKREPORT

The weather forecast shows substantial precipitation for many regions from Thursday through Sunday. Source: Environment Canada

The weather forecast for the weekend shows a major warming trend, with freezing levels reaching upwards of 2000 m over the weekend in southern BC. For northern BC, freezing levels might not get quite as high, but the warm conditions will still have an impact. The warming alone has the potential to wake up the buried weak layer from late January as the snow above it finally begins to settle into a cohesive slab. 

For coastal regions, the problem should be obvious. Periods of heavy precipitation, along with strong winds and rising freezing levels, will create high avalanche danger, and natural avalanches should be expected. It’s not an unusual scenario. If you’re recreating in these areas, managing the problem is simple: avoid avalanche terrain. Steering clear of the storm slab problem means you’ll also be out of the way of any surprising deeper releases or step-down avalanches.

For the interior, conditions will be trickier to manage. Incremental loading means that each consecutive snowfall will increase the load over our weak layers as a new storm slab develops. At some point, we will reach a tipping point where widespread avalanche activity is possible, but when will it be? Given the uncertainty, we need to take a conservative approach. Watch your local avalanche forecast for increasing danger, and stay alert to changing conditions in the field. 

Wherever you’re recreating this weekend, your choice of terrain needs to reflect the changing conditions. As avalanche danger ramps up, we’ll be limiting our exposure to avalanche slopes and enjoying lower-angle terrain without exposing ourselves to overhead avalanche hazards.

This avalanche failed on the weak layer from late January in terrain impacted by the wind near Whistler early in February. The weak layer remains a concern throughout southern BC. Source: MIN user STERLING.CHRISTENSON

The incoming storm snow will bury a weak layer which formed during the recent period of cold and dry conditions in February. Credit MIN User ANDREW.SACHS1

 One thing is certain, it’s time to dial back our exposure to avalanche terrain.

New Snow, Old Problems

Light, powdery snow is the stuff most recreationists dream of and light, powdery snow that sticks around for a while is even better! When cold weather preserves these conditions, we can see lower avalanche danger and the potential for a touch of complacency about the risks. 

We’re always looking to verify conditions as we move through the mountains, it’s an essential part of avalanche safety. When we have loose surface snow, one of the main things on our radar is identifying where this snow has formed a slab. Once we have a slab formed, the avalanche danger can change dramatically—especially where we have a weak layer beneath the new snow. 

A cohesive slab isolated in a snowpit test.

A slab forms when snow crystals form a stronger bond to each other than they do to the layer underneath, which can cause an unstable snowpack structure. You can think of it like a block sitting over marbles. 

A slab can be made of multiple layers that have bonded together, but fails as a cohesive unit on a weak layer. They can range from centimeters to meters deep and the size of the slab determines how much snow is available to move if there is an avalanche. A slab can form in small features, like pockets below a ridgeline, open treeline features, or along road banks. They can also form over large areas, like open slopes or bowls. If a uniform slab is connected through a large piece of terrain, avalanches can propagate widely. 

An avalanche caused by a slab that formed over a large uniform area.

Slabs can feel hard or soft depending on grain size, grain type, and the bond between crystals, but the important thing is whether a slab exists or not.

Sometimes, cracks that propagate through the snowpack are a sign that the surface snow has formed a cohesive unit. Shooting cracks under the weight of a person or machine are a sign of instability in the snowpack. We don’t always get these obvious clues that there is a slab forming though. 

Slab avalanches that have occurred in the last 48 hours are a clear sign slab properties exist in the snowpack. Terrain features on the same aspect and elevation are likely have the same slab properties.

Wind transport at ridgeline and wind drifted snow is another sign that slabs may be forming in the surface layer snow in wind affected areas.

A crack propagating under the weight of a machine. 

Snow that is forming a slab can physically feel different. It can be denser and firmer. If the snow feels stiffer underfoot or you can feel resistance if you put your pole or hand through the layer and lift, there may be a slab. 

Whumpfing is the sound made as a weak layer collapses. If there is a slab in the snow above the weak layer when that happens, and the slope angle is steep enough for the snow to slide, there will be an avalanche. We can also get whumpfs as we’re moving on mellow terrain too and they’re always a clear sign that the snowpack is unstable.

Digging a snow pit and completing compression tests or doing a hand shear test can help you identify slab properties. If a cohesive layer of snow breaks off of your column during a test, it's one sign that a slab is present.

Snowfall More than 30 cm of snowfall or heavy snowfall over a 24-hour period.

Settlement Settlement refers to the process that consolidates snow. It occurs as a result of snow metamorphism combined with gravity’s compression of grains in the snowpack.

Wind As wind redistributes snow, the snow crystals are broken into small particles and become packed together on lee slopes, creating harder density snow. 

Temperature Warm temperatures promote snow grains to round and bond. This settles snow into a cohesive slab. Cold temperatures promote faceting and don’t cause cohesion in the snow. 

Solar Input The sun also causes warming and settling, which can encourage slabs to form. 

When there is potential for slab avalanches, we need to make sure our backcountry travel plans are adapted for this risk. Sometimes there are obvious clues that a slab has formed, but other times being caught in an avalanche is the first obvious sign of instability that you get.

If you are uncertain about the possibility of slab avalanches, terrain choice is your best defense. Ride as if a slab is present until you have enough information to confidently rule it out. This means sticking to low-angled terrain and avoiding convex rolls, as well as travelling on high points, wide ridgetops, and benches to help reduce the chances of triggering a slab.

A snowmobile remote triggers a slab formed in a small pocket. Photo: Frozen Pirate.

What is a Slab?

A crust buried mid-storm produced reactive conditions on Feb. 2 in Vancouver's North Shore mountains. MIN report from brento.

Last week we published a forecaster blog about shifting our mindset and stepping back as stormy conditions brought a sharp rise in avalanche danger. Widespread weak layers of surface hoar, facets, and hard crusts are now buried around 30 to 60 cm deep in the interior and up to 80 cm deep on the coast.   

As we return to cold and dry conditions, avalanche danger will likely remain elevated due to these buried layers. Maintaining a conservative mindset is key as these challenging conditions continue.

The Mountain Information Network (MIN) lit up over the weekend as people headed into the backcountry–thanks to everyone who posted! These observations help our forecasters and other recreationists. Most reported obvious signs of instability, even in conservative terrain. Several observers even noted slab avalanches on lower-angle slopes, around 26 degrees, which is typical of buried weak layers like surface hoar and facets. 

Storm snow takes longer to stabilize and weak layers are preserved in cold temperatures, so it’s time to embrace simple or non-avalanche terrain depending on your local avalanche forecast. Stick to low-angle or densely forested areas and look for options to reduce your exposure to avalanche terrain. While natural activity will likely decrease over the coming days, human triggering of avalanches will remain a concern for some time.

Here’s a reminder of some key signs of instability to watch out for: 

Remotely-triggered avalanches, often triggered from flatter terrain adjacent to a slope, e.g., ridge crests, benches, or areas below steep slopes.

Whumpfing, which is the collapse of a buried weak layer. It is often associated with a distinct “whumpf” sound. 

Shooting cracks in the snow that propagate away from you.

These all are red flags of an unstable snowpack that’s primed for triggering avalanches. Think of it as free advice from the snowpack itself—time to step back and reassess your plan.

Here are some recent MIN images to highlight some avalanches, observations, and signs of instability from around BC. 

This rider-triggered slab occurred on a 26 degree slope on Feb. 2, near Terrace. MIN report from gordweary.

Extensive cracking within the storm snow near Nelson on Feb. 1. MIN report from c.dierker.

This size 2.5 slab was remotely triggered near Pemberton on Feb. 1. MIN report from willvg7.

This slab was remotely triggered by riders as they were descending near Squamish on Feb. 1. MIN report from christieimages155.

A skier remote observed near near McGregor on Feb. 2. The group also had an avalanche incident that they highlight in the MIN. MIN report from ben-hawkins. 

When the snowpack is giving you free advice, take it

Keeping a Conservative Mindset

After a lengthy period of low avalanche danger for the southern half of western Canada, conditions are changing and it is now time to shift our mindset in the backcountry. Many regions will undergo a major increase in avalanche danger as stormy weather returns. The past three weeks of dry conditions formed layers that new snow won’t bond with. As new snow accumulates and forms slabs over these layers, we expect large and dangerous avalanches to be triggered both naturally and by humans. These avalanches are likely to propagate widely across slopes.

Weak surface hoar crystals grew on the snow surface over the past few weeks in many regions, which new snow won’t bond well to (Photo from Hyland Backcountry in the North Rockies).

What this means is that we all have to adapt our mindset and step back. Here are some travel tips to help:

Sticking to dense forests or slopes shallower than 25 degrees without overhead hazard is the best way to stay safe.

Dial back your terrain choices and even avoid avalanche terrain altogether as new snow accumulates. 

Stay away from terrain traps, such as cliffs and gullies.

Assess for conditions as you travel, looking for signs of instability: recent avalanches, whumpfing, and shooting cracks.

Consider that you could trigger an avalanche from a safe spot that releases on adjacent or overhead steeper slopes (remote trigger). 

Always be aware of what is overhead and if there are others around you.

Stay disciplined and don’t let powder fever lure you into terrain capable of  producing large avalanches.

Keep in mind that deeper slabs will likely be found in wind-exposed terrain, which means larger avalanches if triggered.

Ensure that each member of your group is engaged in disciplined terrain selection.

We all want to enjoy the snow and come home safe at the end of the day. Remembering to follow these travel tips will help make sure that happens.

An avalanche that propagated widely in northwest B.C., providing an example of what avalanches may look like as new slabs form in the southern half of Western Canada.

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