After several winters of low snowpacks and challenging avalanche conditions, this season has started with a refreshing return to "average." How average? As of December 15, the BC River Forecast Centre reported that the provincial snow depth was 102% of normal—about as typical as it gets!

Basin snow water index from the BC River Forecast Centre’s Snow Conditions Commentary for December 15.

November brought steady storms, building a solid snowpack without many notable weak layers or crusts. Most regions now have enough snow at treeline for great recreation: around 150 cm in the Coast and Columbias, and 100 cm in the Rockies.

Early December brought a dry spell, creating a mix of layers like surface hoar, rain crusts, and sun crusts. These layers can become problematic when buried, and while some avalanches have occurred on them, the issues seem sparse and likely short-lived in most areas. Recent activity has been most notable in BC’s southern Interior, particularly the southern Selkirks. Northeast of Pemberton is also suspect.

Webcams showing 25 to 50 cm of new snow on December 18.

December looks set to end with a bang. A storm on December 18 brought 25 to 50 cm of snow to southern BC and Alberta. And the action isn’t over yet—several frontal systems are lined up to bring more snow in the coming week.

The 500 mb forecast from the Mountain Weather Forecast shows a parade of storms hitting western Canada for the next week.

What to expect in the coming week? Avalanche danger will rise and fall with each storm as new snow and wind build reactive slabs. During storms, choose more conservative terrain and avoid steep, exposed areas. Afterward, start on low-angle slopes that are too small to produce large avalanches to assess the snowpack before considering venturing into steeper terrain.

What about the weak layers? In some regions, uncertainty remains about how long the early December weak layers will persist and which types of terrain will be most affected. Check your local forecast and if a persistent slab avalanche problem is listed, take a more conservative approach.

We’ll see what the rest of the season brings, but for now, we’ll gladly take an average snowpack without many significant weak layers. Wishing you a fun and safe holiday season!

A Refreshing Start to Winter

Daily avalanche forecasts are about to start for the season and winter backcountry recreationists are already getting into the mountains. 

AvCan team hard at work preparing for the first forecasts.

Travel is still a bit rugged down low, but as you gain elevation, you’ll find that there are fewer ground obstacles impeding your travel and the snowpack is likely above the threshold depth for avalanches. In many places, this transition is now somewhere below treeline and several Mountain Information Network (MIN) users across the province have already reported human-triggered avalanches.

Nov 18 Harvey Pass, southeast of Fernie Photo: MIN user DYLANSIGGERS

Nov 18 The Gorge, west of Revelstoke. Photo: anonymous MIN user

A bomb cyclone is currently lingering off the southwest coast of BC. This weather phenomenon is different from a run-of-the-mill storm because the atmospheric pressure in the center of the low drops very rapidly. This intensifies stormy weather driven by the low pressure system. We have already seen the effects of this on Vancouver Island and the south coast, with high winds and heavy precipitation. Coastal areas further north of the low are experiencing amplified outflow winds. The extreme weather conditions have not spread into the interior of the province. 

As the bomb cyclone weakens and shifts west, the intensity of the storm will decrease, but stormy weather is expected to continue for southern BC into the weekend. It’s likely we’ll see storm and wind slab avalanche problems for most avalanche forecasts over the weekend.

Bomb Cyclone moving west. Source: Mountain Weather Forecast

In parts of the interior mountain ranges that have seen less snowfall and cooler temperatures, a frozen crust buried in November is likely to be coupled with weak layers like facets or surface hoar. This is the case in some of the avalanches already reported, and the forecasted weather is not likely to improve avalanche conditions for these places.

Nov 17th Shovelnose, west of Whistler. Photo: MIN user KYLE_G1

Nov 16 West of Tumbler Ridge, North Rockies. Photo: MIN user DAVE

As you get a handle on avalanche conditions and get your winter legs under you, it’s looking like it will be a good time to start with small, mellow slopes where buried hazards like stumps, rocks, creeks, and larger terrain traps are easy to spot and avoid. As always, it will be important to check your local avalanche forecast and MINs in your area before heading out this weekend. The changing weather and setup of the snowpack mean that conditions could change quickly, so it’s important to get the most up to date information. The first daily forecast for Friday, November 22 will be published on the evening of the 21st.

Nov 13th Mt. Harvey, northeast of Smithers. Photo: MIN user HYLAND BACKCOUNTRY

Any Fallout From The ‘BOMB’?

Your guide to interpreting meteograms and interpreting them into your planning process. 

Meteograms are weather forecast diagrams created by Environment and Climate Change Canada (ECCC). As public avalanche forecasters, we use these on a daily basis as part of our forecasting workflow. They are a highly valuable and freely available resource that you too can incorporate into your daily process. You can find them on our website in the weather section. 

Although they can seem overwhelming, but once you learn how to read them, they're full of helpful information.

There are three choices of model you can use in your meteograms, which you can select using the drop down on the top left of the screen. They are the HRDPS, RDPS, and GDPS. We use each model for slightly different purposes. 

HRDPS (High Resolution Deterministic Prediction System)

This is a short-range and high-resolution model. It gives a prediction for 48 hours in the future across a 2.5 km square area. Usually, this model is the most accurate for short-term weather forecasting and often best reflects the mountain environment.

RDPS (Regional Deterministic Prediction System)

This is a medium-range and mid-resolution model. It predicts 84 hours into the future for a 10 km square area. This model doesn't account as well for mountainous terrain, but it is very helpful for spotting trends in the weather forecasts. 

GDPS (Global Deterministic Prediction System)

This is a long-range and low-resolution model. It predicts 10 days into the future for a 15 km square area. Due to the long term nature of this forecast, it may be less accurate in the short-term. We mainly use this for long-term planning. 

The meteograms are issued 4 times a day. They use Zulu time, which is a standardized time zone. For our purposes, we don't need to worry too much about Zulu time—we're just going to use the most recent one. 

We can choose between point meteograms or group meteograms. Point meteograms provide a forecast for one specific location and group meteograms summarize the information for a wider region and forecasts based on that.

A group meteogram can help us to understand the regional extent of the weather, pick out trends, or find hot spots for snowfall, wind, temperatures, etc. A point meteogram is going to zoom in on one specific area and give you an idea of the weather forecast for that particular area.

There are also (SNL/PT) versions of point and group meteograms that provide additional information about snow level and precipitation type. While this can be useful, the additional information sometimes makes it more difficult to see trends.

In the below example, the red lines show the freezing level and the blue line shows the expected snow line. Typically, we expect the rain-snow line to be 100 m below this line for weak precipitation and up to 300 m below during strong storms. The panels in this type of meteogram also gives you the precipitation types:

At first glance, this is a lot of information to process in one diagram! Let's break it down and start with the top panels.

This will tell you the location, with GPS coordinates, typical treeline elevation for that area, and the model grid point elevation. It will also give you the date and the model run. 

The green shading is telling us the relative humidity at different elevations. Dark green means high relative humidity, white is low. The black lines are humidity contours. As a rough rule of thumb, 80% relative humidity means it will be cloudy, 100% means precipitation, and the white areas suggest clear skies.

The chart also tells us about expected winds. The black wind barbs show the wind speed and direction at different elevations.

The barbs point in the direction the wind is expected to come from. You can also use the next panel down to learn about wind speeds at 2,000 m and 3,000 m elevations. The top panel is usually more accurate for learning about wind where you will be recreating though. 

The dashed red lines show the air temperature at different elevations (shown on the vertical access). 

The solid yellow line indicates the typical treeline elevation in that area. The dashed yellow line is the model grid point elevation, this means there is no data below that elevation. 

The bold red line indicates the freezing level. 

Let's skip down to the cloud cover panel. 

The blue line here shows the percentage of cloud cover. You can use his with the relative humidity data to get an idea of cloud heights and layers. 

The red line is shortwave radiation. This basically means how strong the sun is expected to be. We measure this in watts per meter squared. The influence this will have on the snowpack depend so on the surface snow conditions, but we generally consider anything more than 400 W/m as likely to have a strong impact on sun-exposed slopes. 

The next panel gives us information about the air temperature. Although this information shows us the difference between the air temperature (red line) and the dew point (blue), most meteograms are too low to be helpful for mountain forecasting. Often the first panel is more helpful for our planning.

This panel gives us the 12 hours QPF (qualitative precipitation forecast). It tells us how much snow or rain we're expecting and we measure it in millimetres. The red numbers show minimum, average, and maximum QPF for the 12-hour period between 4 AM to 4 PM (or 6Z and 18Z!) and 4 PM to 4 AM.

When we're dealing with snow, the amount of precipitation doesn't always result in a uniform amount of snow. To work out how much snow to expect from each millimetre of precipitation, we use the snow to liquid ratio (SLR). SLR is linked to temperature, colder air tends to produce higher SLR (15:1 or 20:1) and give us lighter, fluffy powder snow. Warmer temperatures usually mean a lower SLR (7:1 or 5:1) and denser snow, which is excellent for making snowballs.

I consider the world of weather forecasting to be a bit of a dark art. Meteorologists are literally trying to pin down a moving target to determine the exact track, timing, and intensity of a frontal system. It's essential that you verify the weather conditions in the field, in the same way that you are verifying the snowpack, because the two are very deeply related. 

There are so many fascinating things to learn about the complex and dynamic phenomenon of mountain weather. In the winter, reading the Mountain Weather Forecast on a daily basis is the perfect place to start to build a foundational knowledge of weather and start your trip planning on the right foot. There are many other freely available resources that can help in your knowledge and trip planning, here are a list of some of my favorites: 

 ARFI- Designed to help private and public avalanche forecasters, guides, and recreationalists. ARFI was developed by the Applied Snow and Avalanche Research Group at the University of Calgary (ASARC). Around 2014, the ownership of ARFI was transferred to Avalanche Canada.

 VizaWeb- The site is awkward and cumbersome to use but provided a great visual of precipitation hotspots. This is I would generally set up the viewer to look at total precipitation accumulation. 

The GFA- The GFA (Graphical Forecast Area) Is produced primarily for pilots by NavCanada.Learning the different symbols and and abbreviations takes some time, but can help with your analysis of visibility/cloud cover, wind and precipitation.

SpotWx- Designed as a spot weather forecasting tool. It offers a variety of weather models and offers data insimilar charts as the meteograms, but without the visual top panel. I usually look at SpotWx to compare models. If there is a lot of model disagreement in the weather forecast I may factor that uncertainty into my trip plan.

Canada RASP- This site was created by a paraglider and provides two visualizations from the HRDPS model. One is a map that primarily shows information about wind at different elevations, and the other is a ‘windgram’ which shows wind and temperature at a single location as a function of altitude over the next one or two days. This windgram also shows atmospheric stability, which can give an indication of enhanced or convective precipitation (especially in the spring!)

Getting the (meteo)Gram!

April 25 is the last day of daily avalanche forecasts in Avalanche Canada’s forecast regions. Danger ratings expire on April 28 and as of April 29, Avalanche Canada’s forecast regions will list Spring Conditions.

Spring is the time of year when conditions can change in the matter of hours. The weather can switch from a wintry storm to intense summer heat quickly, which rapidly affects the snowpack and avalanche conditions.

Although the daily avalanche forecasts for our regions are finished for the season, there are still some great resources to help you plan for a safe day in the backcountry:

Our Spring Guidance can help you plan for the various conditions you may come across this spring. It breaks the spring up into four scenarios, based on the weather, snowpack, potential avalanche activity, and associated terrain and travel advice. This is the go-to for spring travel in avalanche terrain.

The Mountain Information Network hosts observations by fellow recreationists. The blue pins on the avalanche.ca homepage show the shared information. If you do head into the backcountry, please consider submitting your observations to help others. Even just a photograph helps.

Look for nearby Mountain Condition Reports on the homepage too. They show up as blue pins, but with white circles inside them. These reports include high-quality data, submitted by certified professional guides.

Check the Snowpack Summary section for your region of interest on avalanche.ca for a generalized description of the snowpack.

The Dangerator can be a helpful tool to assess for potential avalanche danger if conditions are wintry.

Review the information on the Mountain Weather Forecast page and associated weather products to understand what weather conditions you may experience during your travels. Although the text that summarizes the information may not be available mid-spring into the summer, the graphics can still provide valuable insights. 

Terrain and travel advice will vary for a given day and location, but here are some general tips for safe travel in the spring:

Aim to start your day early and end your day early, particularly during warm, sunny days. Sun-exposed slopes could quickly form wet-related avalanches and cornices could weaken and fail with daytime warming.

If it is stormy, expect storm slab and wind slab avalanche problems at higher elevations. Dial back your terrain choices and give some time for the new snow to bond, particularly if it is sitting on hard, smooth surfaces.

Expect to find very different conditions with elevation and aspect. The snow may be a hard, melting brick below treeline, but a cold snowpack with weak layers may exist in the alpine. Dry snow may persist on shaded slopes while sunny slopes bake in the sun.

Get at it safely, make some memories, and please report your findings to the MIN to help the backcountry community. We’ll see you in November!

Resources for spring in the backcountry

For many mountain sports enthusiasts, spring is their favorite season. The mountains lure us in with a greater potential for good visibility and comfortable temperatures. If you are a skier, mountaineer, or sledder, you know some of the best alpine conditions are found late March into early May. For those into hiking or biking, the valley bottoms will start to melt out providing great low elevation adventures, but spring is not without its challenges.

Loose wet avalanches, like this one in the North Rockies, are common in the spring.

The trick to having a good time in the mountains in spring is understanding the mixed bag of conditions waiting for you. It may be summer at valley bottom and winter on the summit—with a bit of everything in between. This time of year, a good avalanche forecast and knowledge of mountain weather is invaluable in your quest for adventure.

Just like any other day, we start by looking at the avalanche forecast. We want to pay close attention to the elevation and aspect for each problem. Where on our proposed route will we be exposed to each problem? 

Wet loose avalanches are likely to be a problem on east aspects earlier in the day, and become a concern on south and west aspects as the day progresses. At lower elevations, daytime warming and the resulting rise in freezing level may increase the likelihood of this problem.

During periods of rapid warming, large persistent or deep persistent slab avalanches may run all the way to valley bottoms. You may be hiking or biking on dry low elevation trails and unknowingly be exposed to avalanche danger.

Wind or storm slab avalanche problems may still linger in high north facing alpine terrain.

Cornices are largest in the spring and the chances of them falling increases with solar input and above freezing temperatures. These can be a hazard on their own, but they can also trigger large avalanches on the slopes below. Many recreationists have been killed or injured by simply being on a cornice and causing it to fall.

Cornice falls can cause large avalanches on the slopes beneath. This one was in the Northwest region this week.

Convective flurries are common in the spring. These can be problematic for two reasons. They can result in intense localized wind and precipitation, which can create or worsen a wind or storm slab avalanche problem. They can also surprise recreationists with limited visibility in alpine terrain.

There are also other hazards to consider beyond just avalanche problems. The daily rising and falling of freezing levels, commonly referred to as spring diurnal cycle, will usually form a strong surface crust. When this crust is present early in the morning, the likelihood of triggering avalanches is low. However, in steep terrain, this crust could pose a “slide for life hazard”. Self arresting on this firm smooth surface can be challenging.

There are several resources on our website to help in your spring planning beyond the avalanche forecast. The mountain weather forecast is a great starting point for your morning deep dive into expected conditions. Often it will describe unsettled air and the potential for convection, this can be challenging to pick out in local forecast products. Our weather station list can help you find a station near your objective that can help to verify freezing levels and other weather factors. And of course, the Mountain Information Network is full of valuable conditions reports.

Get the forecast, go further, get home at the end of the day. We will see you out there!

Spring Challenges

The coming days are bringing a significant change of weather and a widespread increase in avalanche danger. A combination of existing snowpack instabilities and unseasonably warm weather means the potential for large and dangerous avalanches. 

A large persistent slab avalanche which failed on the early Feb weak layer in the Monashees near Revelstoke last week. These types of avalanches are expected to continue with the upcoming warming and sun. 

Most of western Canada has been entrenched in a pattern of large human-triggered avalanches since the start of March. The culprit of these persistent slab avalanches is a weak layer above a crust that formed in early February. The behaviour of these avalanches is alarming, with many being triggered remotely, releasing in low angle terrain, and starting part way down slopes. These avalanches have persisted almost daily throughout March, despite the layer getting buried deeper and deeper.

Persistent slab avalanche remotely triggered by skiers in lower angle terrain in the Cariboos on March 3 (MIN report from CRAIG HARTMETZ).

Sudden and significant warming is hitting the coast on Thursday and the interior on Friday, with sunny skies and double digit temperatures continuing over the weekend. The impact of this warming is clear—a spike in avalanche danger, with large natural avalanches.

Regions with persistent slab avalanche problems (which includes most of them), can expect very large natural slab avalanches (size 3 to 4!).

Wet loose avalanches will occur on sun-exposed slopes.

Cornices will break, and potentially trigger avalanches on the slopes below.

In addition to natural avalanches, all the above types of avalanches will be very sensitive to human triggering.

Forecasting persistent slab avalanches can be tricky, but under these conditions it is not. The combo of a hyper-sensitive snowpack with intense warming is a recipe for high danger.

Forecast for Whistler village from Environment Climate Change Canada.

Once the warming arrives in your region, we strongly recommend the following precautions:

Choose activities or routes that do not require exposure to avalanche terrain.

Avoid crossing below avalanche paths, including valley bottom trails that pass through runouts.

Remember that many avalanches have been triggered remotely from low angle terrain.

It's a straightforward message – avoid avalanche terrain.

Let's all hope for improved conditions once temperatures return to seasonal norms!

Remotely-triggered avalanche in Kananaskis Country on March 11 (MIN report from MAJOSRNIK).

Warmup Woes

March 3, 2024: Remote triggered from the lookers left, low angle ridge by a group of ski tourers. Cariboo Mountain (MIN user CRAIG HARTMETZ). 

As the Special Public Avalanche Warning (SPAW) ends on March 7 for regions west of the Rockies, it's important to understand that dangerous avalanche conditions are expected to persist in many areas. Buried weak layers within the snowpack remain a significant risk going forward. Apart from in some of our coastal regions (where stormy weather is about to elevate avalanche danger), we are transitioning into a period where it is becoming less likely you’ll trigger an avalanche, but the consequences of an avalanche could still be very high. These persistent weak layers continue to demand respect and it may take weeks or more for these layers to stabilize. Conservative decision-making will remain essential, even with avalanche danger ratings potentially decreasing in some regions.

Remain vigilant and don’t overlook signs of heightened avalanche danger, like fresh avalanches, whumpfs, or shooting cracks. As the weak layer continues to get buried deeper, signs of instability may be less frequent and less obvious. 

Patience will be critical. Don’t be lured into dangerous terrain when there is new snow or sunny weather.

Be diligent about terrain choice. Stick to low-angle terrain without terrain traps, such as cliffs or gullies. 

Minimize overhead exposure. There is lots of recent evidence of remotely triggered avalanches and avalanches that are running far and pulling back into low-angle terrain. 

The following are examples of some of the persistent slab avalanches we have been seeing recently. Avalanches of this nature are expected to persist so continue to check the bulletin daily to see how conditions are evolving and use this to plan your objectives.

March 2, 2024: A large natural avalanche that propagated across the entire feature. Glacier National Park (MIN user CCMSKI)

March 5, 2024: Skier-triggered size 2 avalanche in the Sea to Sky area (MIN user ERIK.EP).

March 4, 2024: Remotely triggered by a ski tourer in the North Coast mountains (MIN user LAMONTAGNE.YANN).

March 4, 2024: Remote triggered large avalanche in the North Purcells (MIN user COLE). 

March 4, 2024: Rider reported no signs of instability in low angle terrain. While stepping out into steeper terrain remote-triggered this avalanche, another size 1 avalanche was sympathetically released just outside the photo. Duffey Lake area (MIN user CHRISRSMITH12). 

March 3, 2024: A wide-propagating avalanche triggered by a snowmobile rider in the South Purcells (MIN user SCOTT.HICKS). 

March 5, 2024: A very large natural avalanche broke ice on the lake below up to 1 km away. Waterton National Park.

After the SPAW

Last week saw arctic air push its way south from the territories into Alberta and British Columbia. By Thursday, it had made its way to the US border and most of BC was experiencing temperatures below -20 °C, with many areas seeing temperatures at valley bottoms below -30 °C. As the arctic front passed over the area, it brought light to moderate precipitation, along with northerly winds exceeding 60 km/h in the alpine. Once the arctic air mass was firmly in place, northerly winds continued in many regions.

Reverse Wind Loading

With the exception of Vancouver Island and the southwest coast, where conditions will be notably different, this weekend looks set to bring a change.  The weather looks more seasonal (warmer and wetter), but what does this mean for those heading into the mountains? You may encounter wind slabs on slopes that are often scoured, and also soft loose new snow that is not sticking well to the old surface layers. Since there are a variety of conditions you may encounter, it will be important to be alert for signs of instability. 

Image from MIN: wind slab triggered in open trees near Revelstoke on Thursday.

The most concerning slopes will be ones where a layer of soft facets is sandwiched between new wind slabs and the old, hard, wind-affected snow. If you've taken an AST 1, you may recall your instructor expressing concern for a slab over a weak layer on a firm sliding surface…

Image from the archives: a weak layer fails between two hard layers in a snowpack test. 

If you're thinking of getting out there, here are some tips to manage this scenario:

Avoid making assumptions based on previous experience in the terrain.

Constantly assess conditions as you move through the mountains.

Look for signs of instability. Sometimes layers of large facets can collapse and make a whumpf,  just like surface hoar.

Get your shovel out and take a look at the layering of the upper snowpack.

But wait, I saved the best piece of information for last. In sheltered terrain, where a slab is less likely to be found, the skiing and sledding is going to be awesome! It shouldn’t be too hard to find great riding this weekend if you plan for the conditions.

The Winds of Change 🌬️

Last winter, avalanche forecasts in Canada switched from fixed regions to a new system where region boundaries can change based on backcountry conditions. To implement this system, we created "subregions" from our old, large regions. We initially thought this could be done mainly by analyzing terrain and climate factors, but the process ended up heavily focusing on other factors such as backcountry usage patterns alongside terrain and climate. It was a fascinating process for us in the forecasting team, and it inspired us to write this blog for map “keeners” who want to know how Canadian forecast regions were split into 123 subregions.

Progression of public forecast regions in western Canada from 1998, 2004, 2012, 2021, and 2024 (regions for Quebec and Newfoundland are not shown).

Terrain, climate, and recreation patterns

In the summer of 2022, forecasters were tasked with splitting their large regions into smaller polygons that could be dynamically grouped. There were some obvious splits, like separating the Duffey and Coquihalla areas in the former South Coast Inland region, while other areas had less clear criteria that required digging deeper. We supplemented our existing knowledge of the regions with several datasets:

Defined boundaries from regional districts (e.g., watersheds, wildlife management units, biogeoclimatic regions).

Terrain data including elevation and land cover (e.g., forest type, treeline elevation, glaciation).

Precipitation and temperature climatologies.

Historical locations of Mountain Information Network reports.

Areas in the Trip Planner with Avalanche Terrain Exposure Scale ratings.

Locations of critical data sources such as automated weather stations and professional avalanche operations.

Physical factors considered included terrain and climate. The left image shows elevations (m) in the south coast and the right image shows the annual precipitation (mm) from PRISM.

In many cases, neither pre-defined regions nor an automated analysis of physical terrain and climate factors produced results that made sense from the perspective of backcountry recreation. It became clear the top priority should be creating regions that split backcountry recreation areas into groups that often experience distinct avalanche conditions. When looking at our proxies for recreational use (e.g., MIN reports, ATES-rated areas), the necessary subregions became fairly obvious. Except for some of the more remote areas, where usage patterns were unclear and terrain and climate factors had to play a bigger role.

Proxies for recreational patterns in the south coast included historic MIN report locations (brown dots) and ATES-rated areas in the Trip Planner (purple polygons).

Once we established key recreation areas, a technical challenge became drawing the boundaries between subregions. A primary consideration was to avoid drawing boundaries through recreation areas. This way someone planning a trip would only need to read one forecast, as opposed to travelling through multiple forecast regions in a single day trip. This typically led to drawing boundaries in low terrain (e.g., following rivers and roads, passing through cols) rather than high terrain (e.g., following watersheds, ridgelines, and peaks).

Subregion boundaries in the Terrace area primarily follow low terrain.

Dividing subregions with low terrain produces subregions that contain both the wet and dry sides of mountain ranges, which leaves climatic variability within each subregion as the windward side of ranges tends to be wetter. However, wet and dry areas within a mountain range rarely follow obvious lines and typically require extensive local knowledge of how weather systems interact with the terrain. We used different methods to carefully delineate wet and dry areas wherever possible, using local knowledge and even forestry data in some places. (Wet areas tended to have more hemlock and cedar, as opposed to pine and fir in the dry areas.)

The subregion boundary in the central Purcells was divided into wet and dry areas using local knowledge.

The draft subregions from each forecasting agency were merged into a master map to cover all Canadian avalanche forecasts. Avalanche Canada, Avalanche Quebec, Banff Yoho Kootenay National Parks, Jasper National Park, and Kananaskis Country created new subregions, while Glacier and Waterton National Parks did not subdivide their areas. The merged map was fine-tuned using QGIS and then published in geojson, kml, and shapefile formats at https://github.com/avalanche-canada/forecast-polygons. This map was imported into our forecast publishing software, where forecasters can dynamically group and move subregions between forecasts.

Screenshot of our forecast publishing software showing a draft arrangement of forecast regions and danger ratings for the south coast.

We used the flexible system for the first time in the 2022-23 winter. While there was a learning curve, it ultimately allowed us to create more homogenous and representative forecast regions. Common reasons for changing region boundaries are storm tracks, which inform the distribution of storm and wind slab avalanche problems, and snowpack observations, which inform the distribution of persistent and deep persistent slab avalanche problems.

A hypothetical example of a storm track moving from Vancouver to Hope with bands of decreasing danger level towards the north.

Ryan Buhler, our Forecast Program Supervisor, wrote a paper for the 2023 International Snow Science Workshop analyzing the grouping of subregions during their inaugural season (link below). Based on experience from this first winter, minor revisions to the subregions were made over the 2023 summer. During the first few weeks of the 2023-24 winter, our forecasters have been applying the dynamic regions more fluidly as we become more familiar with the new system.

Read about the basics of the system at Flexible Forecast FAQs.

Map of subregions and data sources at ARFI. 

ISSW paper: An analysis of Avalanche Canada's flexible forecast regions.

ISSW paper: The AvID project: Collaborative solutions to avalanche forecasting challenges.

Redrawing forecast regions—the maps behind flexible forecasts

The 2023-24 season has started very dry with an unusually shallow snowpack. Many of the snow stations with historical snow data are showing near-record lows, some dating back a few decades. The main concern with a shallow snowpack is that weak layers are easier to trigger for a longer time, and they often become even weaker over time.

There are two layers currently at play: a layer of surface hoar buried at the start of December, and basal facets. These two weak layers recently caused several large avalanches in the Selkirks around Revelstoke and extending north into the Cariboo Mountains around Valemount. While most of the natural avalanches occurred Dec 23 – 25, sporadic avalanche activity continues. 

This article primarily addresses the Columbia Mountains, but it's noteworthy that the Purcells and central Rockies, which are generally characterized by a thinner snowpack, have been reporting deep persistent slab problems for at least a couple of weeks now. This MIN post shows a recent example of a deep slab avalanche in the central Rockies.

The snow pillow on Mount Revelstoke is showing near-record low snowpack, since 1992 (source)

A deeper dive into the shallow snowpack problems

Two deep avalanches are suspected to have been remotely triggered at 2100 m on a southwest aspect in the Monashee Mountains south of Blue River on Dec 23. (Photo: Willy Rens)

The persistent and deep persistent avalanche problems we’re seeing in these regions are primarily found in the alpine. While temperatures have generally been quite mild this season at lower elevations, it’s likely been cold enough to result in faceting snowpack gradients at higher elevations, especially in wind-exposed terrain where the snowpack remains thin. 

The surface hoar layer exists at treeline and in the alpine and has been reactive for most of December in many of the interior regions (see this blog from Dec. 15 for more details). In the regions south of Revelstoke, a rain crust has made it more difficult to trigger this layer and has limited the amount of avalanche activity. Further north where that rain crust is thinner or doesn’t exist, recent milder temperatures appear to be causing the layer to gain strength at treeline elevations. 

However, while it’s uncertain where and at what elevations this surface hoar layer continues to exist; professionals are still treating it with respect. Expect it to remain intact and reactive in some areas in the alpine. 

Basal facets are the other concern in thin alpine snowpacks. While temperatures have not been unusually cold like last year, the combination of a very shallow snowpack with seasonal alpine temperatures has likely been enough to result in a faceting temperature gradient. As a result, layers near the base of the snowpack may be getting progressively weaker. For more details on snowpack faceting and temperature gradients, check out this blog from last year. 

An estimate on locations where the two deep weak layers may be reactive.

Whenever problems like this start to develop, I immediately look to the guiding community and see how they are managing their terrain use. In addition to conservative terrain selection, they are also: 

Sticking to low-angle slopes and avoiding large, smooth, and steep features, especially in the alpine.

Avoiding recently wind-loaded terrain features.

Riding smaller slopes at treeline and below, where a bridging rain crust is known to exist.

While natural avalanche activity in the interior ranges has tapered off in recent days, there remains a lot of uncertainty about what the future holds for these weak layers. Relatively dry conditions are expected to persist for at least another week. These are ideal conditions for snowpack faceting to continue, especially where it’s thin at higher elevations. This means the basal faceting could get worse before it gets better. 

The major tipping point for another substantial round of natural activity on the deep layers will likely be the next big storm. However, the long-range weather forecast remains relatively dry for at least the next week in the interior. By the time we get the next big storm, it’s possible that the surface hoar problem may have improved, and the basal facet problem may have worsened. We will continue to monitor both layers, so keep an eye on the bulletins for ongoing information on these problems. 

Some examples of recent large, deep avalanches in the Columbia Mountains:

In the Selkirks east of Revelstoke on Dec 24, a large natural avalanche on solar aspect scrubbed down to rocks, and numerous other smaller releases in the same terrain. (Photo: Andrew McNab)

This avalanche at 2300 m on a northeast aspect likely initiated on the early-Dec surface hoar and scrubbed a small pocket down to the basal facets in the Selkirk Mountains east of Revelstoke on Dec 23. (Photo: Sean Cochrane)

A human-triggered avalanche at 2300 m on an east aspect failed on basal facets in the Selkirk Mountains northwest of Golden on Dec 25. 

Wind loading is the expected cause of this natural avalanche at 2200 m on an east aspect in the Selkirk Mountains northwest of Golden on Dec 23. The avalanche failed on the early December surface hoar and stepped down or scrubbed down to the ground in many places. 

A MIN report from the Selkirk Mountains north of Revelstoke on Dec 27: multiple natural avalanches were observed on south and east-facing aspects. All were on steep rocky peaks and ridges that let go of the whole slab/layer to rock. (MIN Report and Photo: HIGHPERFORMANCEINDUSTRIES)

Blogues