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.

Shifting Your Mindset

Whether you're a seasoned professional or a recreationist, building a strong mental model of the current conditions is essential for making informed decisions in avalanche terrain. Professionals returning after time away or joining a new operation start by gathering and reviewing critical information during shift handovers. This includes snowpack analyses, significant avalanche observations, layers of concern, and areas of uncertainty. Beyond collecting data, they assess the weight of each piece of information and how it shapes the bigger picture, ensuring sound decision-making in high-pressure environments.

Recreationists follow a similar process when they follow the Daily Process. Reviewing past and current weather data, analyzing the avalanche forecast in detail, and consulting MIN posts or local social media are key steps. Recording this information in a field book is a helpful practice, especially when internet access is limited, as it allows you to track critical factors throughout your trip. Together, these strategies form the foundation for safer and more effective decision-making in the backcountry.

Observations are an essential part of a strong mental model.

How to Use Your Mental Model in the Field

Once you’ve established a baseline mental model, you’ll need to maintain and strengthen it. Remember in constantly changing and dynamic environments, your mental model becomes stale unless you are continually updating it. This is the basis of situational awareness. 

A remotely-triggered, deep persistent slab avalanche in the North Rockies. A good reminder of the consequences of our decision making.

Let’s take a look at a simple example and some strategies we could use to maintain and strengthen our mental model: the sun unexpectedly emerges and is rapidly warming the air and snow surface. 

This information may well change the way we plan to move through the mountains. Let’s break down how we might need to update our mental model. 

We’ll start by thinking about what clues you might have noticed to tell you it was getting warm.

The surface of the snow becoming sticky and heavy.

Snow beginning to fall from trees, or small snowballs or pinwheels are starting to roll off rocks. 

Next we need to think about this information is telling you about the state of the snowpack.

The surface of the snow is changing rapidly. 

Small loose wet avalanches may now be possible.

In bigger terrain above you, the loose and dry snow may be rapidly settling into a slab. 

If there are deeper snowpack instabilities, they may begin to wake up.

All of these hints and clues tell us that we need to make changes to our mental model. We are no longer travelling in the same conditions we set out in, and we need to make sure we’re adapting. Ask yourself:

You’ve made an assessment that the snowpack conditions and weather are changing. Is your original route plan still appropriate for these changes?

Does sticking to your plan increase the risk outside of your acceptable range?

If the original route no longer works in the new conditions, it’s time to consider alternatives.

When we don’t work to maintain good situational awareness, our decision-making is often influenced by biases that can lead us into heuristic traps that undermine our careful planning. The first step in addressing these biases is being mindful and aware of their presence. While this blog doesn't detail these factors, understanding them is a fundamental aspect of avalanche safety training. 

As we move through the terrain, here are some key factors we need to keep in mind and work into our dynamic mental model.

Terrain: Identify terrain features, overhead hazards, safe areas, and terrain traps. 

Snowpack: Be aware of rapid snowpack changes, such as heavy snowfall, warming temperatures, or wind transportation of snow. 

Weather: Stay informed about the forecast and keep a sharp eye on changing conditions. If the weather deviates from the forecasted conditions, you’ll need to think about whether the avalanche danger might have changed too. 

Team Communication: Keep checking in with your group. Make sure everyone is on the same page about what you’re doing, why you’re there, and whether any of this has changed during the trip.

Severity: Make sure you’re considering what the consequences of an error might be. Has it changed during the day? What happens if you’re wrong?

A very large loose wet avalanche cycle late in the season North Coast, consequences from being caught in something like this could be severe.

It doesn't happen in the field, but it’s a key step keeping situational awareness skills sharp. After your trip, take the time to reflect and analyze your decisions. Debrief as a group and ask questions like:

Are there times where you think you might have been lucky?

What could you do differently next time? 

Answering these kinds of questions can improve your mindset and make your next adventure that much better. 

If you’d like to learn more about the Daily Process, you can find it here: https://avysavvy.avalanche.ca/en-ca/the-daily-process 

For a more detailed look at heuristic traps, check out this paper by I McCammon: https://arc.lib.montana.edu/snow-science/objects/issw-2002-244-251.pdf 

Heads Up! How to Maintain Situational Awareness During Winter Adventures

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.

Blogues