A "historic avalanche cycle" in the Rocky Mountains has prompted rare "extreme" warnings throughout the national parks west of Calgary and Edmonton — and even some of the most experienced mountaineers say they're planning to stay out of the backcountry this weekend.

"I don't think I've ever seen anything like it," said Sean Prockter, a seasoned climber who lives in Jasper, Alta.

"Another friend of mine, who's also in the mountains, said in 15 years of backcountry skiing in the Rockies, he's never seen such a forecast."

Parks Canada officials continued their recovery effort Friday and finally reached the bodies of two American snowshoers who were buried in an avalanche about 20 kilometres north of Lake Louise.

The pair was reported missing Tuesday and it's believed they were caught in the slide the previous Saturday or Sunday.

The high avalanche hazard had made it difficult for officials to safely reach the area on foot.

'Extreme' avalanche forecast

The current avalanche risk in Banff, Kootenay and Yoho national parks is rated "high" in the alpine, at treeline and below the treeline.

As of Saturday, the forecast is elevated to extreme — the highest possible rating — in the alpine and at treeline throughout the mountain parks, including Jasper.

The Icefields Parkway, which runs 220 kilometres between Jasper and Lake Louise, remained closed Friday for avalanche control and isn't expected to reopen until Sunday evening at the earliest.

Closer to Calgary, the forecast for Kananaskis Country also includes an extreme rating in the alpine this weekend and a high rating at lower elevations.

"None of us have seen a season like this," said Matt Mueller with Kananaskis Country Public Safety Section.

"In terms of backcountry travel, we're just suggesting to avoid it."

'Catastrophic avalanche scenario'

The high-risk situation throughout the Rockies is the culmination of a series of weather events that began early in the season, said James Floyer, the forecast program supervisor with Avalanche Canada.

He said low snowfall early in the winter coupled with extended bursts of extremely cold weather resulted in "weak, sugary snow crystals" near the bottom of the snowpack.

"It has no real strength near the ground and it's waiting for the right conditions, essentially, to create a catastrophic avalanche scenario," Floyer said.

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That arrived by a series of heavy storms in recent weeks that loaded heavy snow on top of that weak layer, followed by a sudden increase in temperature during the past week.

"That warmth has a tendency to really break down the snow surface, and small potential avalanches running on the surface can then trigger deeper avalanches below," Floyer said.

"And that's what we saw happen pretty much throughout the Rockies."

'It's so sketchy out there'

Avalanches of up to size 3.5 — a descriptor used to explain the destructive capacity of a slide — have been "widespread" throughout the region, according to Avalanche Canada.

A size 3 avalanche is powerful enough to destroy a car or a timber-frame building, while a size 4 can knock a freight train off its tracks and wipe out up to four hectares of forest. A size 3.5 slide is somewhere in between.

When it comes to backcountry travel in conditions like that, Prockter figures "just avoiding it altogether" is the best option.

"It's so sketchy out there," he said.

"You can predict all you want, but there might be some pretty unpredictable avalanches that you'd never expect to slide come down."