OGDEN -- As Utah ski resorts anticipate the arrival of the big storm they've been desperately waiting for, experts want to remind eager snow junkies -- especially those who plan to venture into the backcountry -- to be extra careful.
After an unusually dry start to winter, as much as a foot and a half of fresh powder is expected to blanket Northern Utah's mountains over the next several days.
While that's good news for the ski industry, it also dramatically increases the risk of avalanches, which account for nearly two-thirds of natural hazard-related deaths in the state.
The National Weather Service in Salt Lake City is forecasting significant winter storm activity throughout Northern Utah beginning this afternoon and continuing through Monday morning. In the valleys, higher temperatures mean the snow should turn to rain Thursday, but mountain snowfall is expected to continue through the weekend.
From today through Thursday, between 12 and 18 inches of snow are expected to fall in the northern mountains. That's a significant amount for Northern Utah resorts, where bases currently range from about 20 to 36 inches deep.
The lack of snow in recent weeks has made much of the scant snowpack in the mountains brittle and unstable. Drop a thick new coating of snow on top of that, and you have a recipe for high avalanche danger, said Bruce Tremper, director of the Utah Avalanche Center.
Avalanches are caused when a heavy layer of new snow causes the existing snowpack underneath to buckle, sending the new layer tumbling down the slope.
The fact that the snowpack in Utah is well below average for this time of year only increases that risk, Tremper said.
"This thin snowpack is much more dangerous than normal," he said. "It's extremely weak right now."
The effect of a big storm on top of such a weak bottom layer is "like dropping a brick on top of a pile of potato chips," he said.
Until the snowpack has a chance to stabilize, skiers and snowboarders are encouraged to stay within resort boundaries, where trained employees use avalanche-control techniques to address any high-risk areas before the lifts open.
Meanwhile, backcountry snowmobilers should stay off steeper slopes.
Tremper said north- and east-facing slopes will be the most dangerous, especially above 8,000 feet in elevation. Many south- and west-facing slopes are essentially bare, and any snow falling on top of bare ground should remain stable.
He said the situation later this week could be especially dangerous, because so many people have spent several weeks waiting for a good storm to provide the powder conditions they crave.
"We've got a double whammy, with very dangerous avalanche conditions combined with very, very eager people," Tremper said. "It's just a bad combination."
He said the current base layer of snow is what avalanche forecasters call a "persistent weak layer," meaning avalanche danger should remain high for weeks.
"A persistent weak layer has to be equally matched with persistent patience," Tremper said. "This is going to go on for the next couple of weeks, so we had better get used to it."
The Utah Avalanche Center provides daily avalanche danger updates by region on its website, www.utahavalanchecenter.org.
In the meantime, Tremper said, the safest thing to do is to stay off of, and out from underneath, any slopes steeper than about 30 degrees.
"We just want everybody to come back alive."