These three avalanche climates are: maritime, intermountain, and continental. (Intermountain is also sometimes called intercontinental or transitional.)
Maritime snowpacks are generally thick, warm, and strong. Continental is usually thin, cold, and weak. And intermountain lies somewhere in between.
The climates are so named for the regions that they are predominately found in, but true to snow science’s nature, this is not a set rule. The truth is, a snowpack can fluctuate depending on the temperature, weather, snowpack depth, elevation, and so. Given the right conditions a maritime snowpack transform and act like that of a continental climate. And the same is true for the other avalanche climates. So instead of thinking of these avalanche climates as regional, think of them as purely labels that are may favor a particular but are by no means restricted to that region.
It may just save a life
This post summarizes each climate. But please keep in mind, in order to really be able to evaluate the snowpack stability and know whether or not it is safe, much more knowledge is needed. More about that at the end of this article.
The Maritime (Coastal) Avalanche Climate
This snowpack is typically seen in mountains along the coast. Because of this, there tends to be more snowfall from frequent storms and warmer temperatures. The snowpack is deep, often more than 100 inches (3 meters). Freshly fallen snow from these storms has a high density, meaning the new snow weighs more. This heavier snowfall adds stress to the weak layers in the snowpack, so avalanches tend to occur during this time or shortly after. Midwinter rain is another very ordinary occurrence in Maritime climates and can lead to wet avalanches throughout the season.
Speaking of weak layers, the common weaknesses found include layers of low-cohesion (or bonding), and weak interfaces like ice or wind crusts. Weak layers can also result from rain or rapid warming. But do not be fooled, faceted snow, depth hoar, and surface hoar can still occur. For those who need a quick review, these types of snow crystals are typical weak layer and low-cohesion producing culprits.
The Intermountain (Transitional) Avalanche Climate
This snowpack is most associated with mountains that may not be on the coast, but are still influenced by the ocean. Snow depth is not as deep, but not low either, about 50 to 100 inches. (1.5 to 3 meters) Temperatures can ranges from cold to warm, but generally not on the extremes. This means that instabilities in the snowpack can last for days after a storm, especially if it’s followed by a lengthy cold period. Weak layers can be persistent and create problems throughout the season.
The Continental Avalanche Climate
These are the mountains located inland and are rather far from the oceans. Temperatures are more often very cold with storms occurring less frequently. New snowfall is lower density because it is drier than the moist Maritime snow. The snowpack is thinner, only about 70 inches (1.5 meters), but this does not translate to a lower avalanche danger. In fact, there’s a higher avalanche risk because this snowpack can be very complex and hard to evaluate for safety!
Remember the mention of surface hoar, depth hoar, and faceted snow from early? Yeah, these bad boys are rampant weak layers in the continental snowpack. Even worse, they have a tendency to stick around for a very long time, maybe even the entire season. And non-storm related factors are constantly at work within this snowpack, again making safety and stability evaluation more difficult. This is why the best strategy in this climate zone is to avoid likely avalanche terrain.
Thankfully, there are experts to help you make a better decisions. Be sure to fully read the avalanche bulletins and forecasts for your given area. Check out our ever growing list of worldwide avalanche alerts and bulletins here.
Much of the information in this post was taken from Staying Alive in Avalanche Terrain, by Bruce Tremper. Also consider taking a hands on avalanche or snow safety course. It’s a great addition to the medical and first aid knowledge thought in the online Outdoor Safety course.