By Allan Dowd

VANCOUVER (Reuters) - Canada and the United States have adopted a unified warning system to better advise skiers and snowmobilers about the avalanche danger, Canadian officials said on Wednesday.

Canada unveiled the new warning system just days after a big snow slide slammed into a snowmobile rally near Revelstoke, British Columbia, killing two people, although officials said the timing was only a coincidence.

The danger scale, to be implemented next winter, modifies current systems advising people whether it is safe to be in mountain regions, by incorporating both the likelihood and consequences of an avalanche in an area.

The current systems used in both countries warns people about the likelihood of a snow slide, but does not communicate other important information, said Grant Statham, a mountain risk specialist with Parks Canada.

"(The new system) considers factors such as both the likelihood of triggering an avalanche and how big it will be," Statham said. "Its job is to make it easier to understand."

Statham said the danger of several small slides being triggered may be considered less than the likelihood of one very large slide.

Parks Canada, the Canadian Avalanche Center, U.S. Forest Service and Colorado Avalanche Center were among the agencies that spent five years developing and testing the new warning system.

"It's a significant accomplishment," said Doug Abromeit, director of the U.S. Forest Service's avalanche center in Ketchum, Idaho.

Thirty six people died in avalanches in the United States in the winter of 2007-08, with 33 of the fatalities involving people in backcountry recreational activities such as skiing or snowmobiling, according to the U.S. Forest Service.

British Columbia, which sees most of Canada's deadliest avalanches, recorded a record high 24 fatalities last year, according to provincial officials.

Officials said the new system will also remind people that while it warns them about the avalanche risks, the final decision whether to travel into the backcountry is entirely theirs.

"While we will never completely eliminate the risk, this initiative provides backcountry users with another tool to use in conjunction with specific equipment and training to help minimize those risks," Canadian Environment Minister Jim Prentice said in a statement.

The weekend snowmobile rally near Revelstoke on Saturday had attracted some 200 people, despite warnings that the avalanche danger was high. Two people died after many in the group were buried by the snow, and officials had initially feared the death toll was much higher.

Police have launched a criminal investigation into whether there was negligence on the part of organizers or participants in the private event.

(Reporting Allan Dowd; editing by Rob Wilson)