Winter is Here - Trip Planning in Avalanche Terrain

Winter is here! The wait is over! We’ll soon be frolicking through snow covered meadows, soaking the view of white capped peaks, and skiing fluffy powder. We cannot wait.

The photo below was taken at 6,000 ft. on recent hike near Mt. Rainier. The snow is accumulating and it is a beautiful sight to see. This gorgeous snow can also be dangerous on the wrong slopes at the wrong time. Wilderness recreation in winter time demands additional research and knowledge to plan for a safe and successful trip.

A snow covered trail through burned trees against a blue sky.

Do you know how to safely research, plan, and confidently travel in avalanche terrain? Do you know how to identify avalanche terrain? Do you know how to predict and assess the avalanche risk of current snow conditions? We’ve got the resources you need!

There are three primary elements that make up the avalanche risk triangle - avalanche terrain, unstable snow, and trigger. The presence of two or more of these elements should make you sit up and pay attention. Don’t believe us? Check this out and come back in a few moments.

Note: This post is not a substitute for formal avalanche safety education. We urge you to pursue avalanche education and/or take a FREE Northwest Avalanche Center Awareness course. This could save your life.

Avalanche Terrain - What is It?

At a high level, avalanche terrain is defined as snow or ice covered terrain at an angle steep enough for snow to slide downhill. Snow or ice sliding downhill is an avalanche. Avalanche terrain in the Pacific Northwest Cascade range is generally found on or below slopes measuring between a 30 - 50 degree slope.

All backcountry winter users traveling through, on, or under avalanche terrain need to be able to intelligently assess their trip risk. This is done through a combination of factors including identifying avalanche terrain, assessing current snow conditions, and making smart trip planning decisions.

Additional information on identifying avalanche terrain can be found on this excellent Mountain Safety Research blog entry.

Avalanche Terrain - Where Is It?

Does your hike, snowshoe, or other backcountry adventure cross on, through, or below avalanche terrain? How steep and how concerning is this terrain? How do you find out? Meet Caltopo!

Caltopo is a free online mapping resource with local trails and easy to read color coding of avalanche terrain. The ‘Slope Angle’ overlay feature displays an orange to purple color code to alert you to the presence of avalanche prone slope angles. A great tutorial is located here.

You can also download Caltopo maps for offline viewing and use on your mobile phone or GPS device. You can also download a GPX file of your map from the main Caltopo logged in view. (you’ll want this for later on in this post) More information on downloading maps is here.

In short, if the Caltopo Slope Angle display for your adventure area shows orange, red, or purple shading you are in potential avalanche terrain. Now let’s talk about how to tell if there is snow there too, and, if so, how much and in what condition.

A snow and ice covered ridge line.

What About Snow Conditions?

Thankfully snow and ice don’t just slide on their own. Layers of snow and ice on avalanche terrain slopes need two additional factors to slide - unstable snow and a trigger.

The second item in this list - a trigger - is the easiest to address. A trigger is any element that can cause unstable snow to slide by causing a de-stabilizing action. This is most often human activity. If you or others are in avalanche terrain you have a trigger.

The first item - unstable snow conditions - is more complicated to properly predict and assess. A full working knowledge of this topic takes years of time, research, and practice to acquire. Thankfully we have help!

Snow Condition Resources

  1. Snow Depth: Is there snow at the trailhead? On the trail? Snotel will know! Snotel is a series of real-time probe placed throughout the region to monitor current and historical snow depth information.

  2. Northwest Avalanche Center - Snow Conditions & Avalanche Risk:

    The team at the Northwest Avalanche Center posts a daily forecast of avalanche conditions starting in ~early December. Locate the region in which your trail is located and review the current and expected avalanche terrain conditions.

    Want to know more about minimizing risk while traveling in potential avalanche terrain or how to assess changing conditions in the field? The Northwest Avalanche center offers amazing free Avalanche Awareness Education sessions throughout the region. Go. It could save your life.

Putting It Together - Gaia GPS with Slope Angle Overlay

You’ve researched your trail, determined whether or not you are expecting to travel on, through, or below avalanche terrain. You’re also checked in with NWAC and determined whether or not there is a risk of unstable snow in the forecast. Great work!

Now do you combine this information, and your beautiful Caltopo map, into something you can use out on the trail? Our favorite inexpensive GPS solution is Gaia GPS.

Gaia GPS is a web and mobile application based GPS mapping tool. Gaia GPS supports custom trail markers and maps, live GPS location display, .gpx import and export, and offline map downloads for adventures outside of cellular coverage. Gaia GPS is also a more affordable alternative to expensive dedicated GPS devices using your existing Apple or Android phone.

Remember those instructions on how to use Caltopo to download a custom map into a .pdf / .gpx file? Got your file? Awesome! Now let’s import it into Gaia GPS on your mobile device.

First, locate your .gpx file and email it to yourself. Next, open your email on your mobile device, locate the file, and select ‘Open with Gaia GPS’. Nice! Your specific map area should now be visible on the Gaia GPS display. More information is here if needed.

Notice something though? The Slope Angle color shading is gone. Let’s fix that! The Premium edition of Gaia GPS allows you to toggle the Slope Angle overlay on your custom Caltopo map.

You’ll find the Gaia GPS Slope Angle overlay under ‘Premium Layers’ in the upper right button on the application. More information on Premium Layers and how to enable them is located on the Gaia GPS help site.

We are proud to offer a discount of up to 35% off on Gaia GPS Premium Membership plans. Discount details are here for Cascade Mountain Adventure clients. #sponsored

Your resulting map will look something like the one shown below after applying the Gaia GPS Slope Angle Overlay. Make sure to download the map for Offline Use in the Gaia GPS application. This will allow you to use all of the features of Gaia GPS, including real time location display, even outside of cellular coverage areas.


The real time Slope Angle overlay display in Gaia GPS, combined with the forecast information from NWAC, will enable you to know when you are traveling through avalanche terrain and make the appropriate risk decisions for you. When in doubt choose a lower risk hike and/or destination.

We hope this is helpful in learning more about key resources during winter wilderness exploration. As the Northwest Avalanche Center team says, the only successful trip is a round trip. Now is the time to make sure that you know how to make this a reality.

See you the trail! Have a safe, fun, and wonderful wilderness winter season.

Note: This post is not a substitute for formal avalanche safety education. We urge you to pursue avalanche education and/or take a FREE Northwest Avalanche Center Awareness course. This could save your life.

Two hikers on a wilderness trail with patchy snow on the ground. A mountain lake and tree covered mountains in the distance.

Note: This post focuses on essential weather and planning resources for late fall into winter hiking. Need advice on gear too? Excellent! We’ve got that covered right over here.

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