Avalanche Canada is telling backcountry users to exercise caution during warming spring conditions.

The renewed warning comes after a group of five hikers are believed to have fallen to their deaths Saturday from the top of Mount Harvey near Lions Bay, B.C. after a cornice had collapsed.

Karl Klassen, the warning service manager with Avalanche Canada, says cornices — an overhanging shelf or ledge of snow built up from blowing snow — are typically at their largest in the spring.

Changing weather conditions, however, can make them unstable.

"Often when we get rapid temperature changes or the first big warm up of the year, or perhaps it rains higher up on the snow that's already fallen and formed a cornice, they become unstable. They're an avalanche problem," he explained.

Avalanche Canada cornice danger diagram

This diagram from Avalanche Canada shows how a cornice can be dangerous for unaware hikers. (Avalanche Canada)

It can be difficult to see exactly where they begin and end, he said.

"When you're looking at them from below and to the side, they're pretty obvious. They're an overhanging mass of snow," he said.

"It can be difficult to tell where the edge is especially if the light is poor, the weather is bad, or the visibility is limited."

Spring conditions deceptive

Part of the danger with the backcountry at this time of year is warming conditions can be deceiving, Klassen said.

"It feels very spring-like and perhaps doesn't feel very hazardous when you're down in the [Fraser] Valley," he said.

"[But] as soon as you get to a certain elevation, there's certainly still enough snow and we're still seeing avalanches occur throughout the region and on the South Coast and the Sea-to-Sky corridor and across the province."

While Klassen said he wouldn't dissuade people from going into the backcountry at this time of year, he says people need to manage their risks carefully.

"With careful planning, choosing the right terrain at the right place at the right time, you can run a safe trip at this time of year just like any time of year. It's just the conditions are changing."

Listen to more tips from Avalanche Canada's Karl Klassen on CBC's The Early Edition here: