The special bulletin went into effect at 6 a.m. on Dec. 14 and is expected to continue through 6 a.m. on Monday, Dec. 16. The affected mountains include the Wasatch Range, Western Uinta Mountains, and the Bear River Range, the avalanche center said.
"We want to tell people to avoid being on -- or beneath -- steep slopes on the north side of the compass," Drew Hardesty, an avalanche forecaster with the Utah Avalanche Center, told ABC4.com.
Because of heavy snowfall and strong winds, upper-elevation slopes facing northwest, north, northeast, and east are expected to see considerable avalanche danger above 9,500 feet, and moderate danger from 8,000 to 9,500 feet.
The avalanche center said some mountains have received up to 12 inches of snow over the past 36 hours. An approaching storm is expected to bring snow to the mountains throughout Saturday and Sunday.
"Remember that sometimes we're gonna be able to trigger these avalanches remotely -- that means, [people] might be able to trigger them from a distance or even below," Hardesty said. "Very tricky conditions out there."
Hardesty said avalanches rarely happen without warning: "The snowpack talks to you."
He said recreators may see avalanches or shooting cracks, or they may hear "audible, thunderous collapses within the snowpack." He also said backcountry skiers and snowboarders should be prepared to do their own rescues.
To stay in the know about current avalanche conditions, Hardesty recommended checking the avalanche center's website every morning.
Background
Here are some things to know about this weekend's avalanche conditions.
What does 'considerable' danger mean?
Avalanche danger ratings have five different levels: Low, moderate, considerable, high, and extreme. This weekend's danger levels are at moderate and considerable levels.
Considerable danger means "dangerous avalanche conditions" -- with natural avalanches possible, and human-triggered avalanches likely.
Moderate danger means "heightened avalanche conditions on specific terrain features," with natural avalanches being unlikely while human-caused avalanches are possible, according to the avalanche center.
"Most avalanche fatalities occur at Considerable danger because the maximum interaction between people and avalanches occurs there," the avalanche center explains.
Special Avalanche Bulletin vs. Avalanche Watch
The Utah Avalanche Center issues three levels of public notices: A Special Avalanche Bulletin, an Avalanche Watch, and an Avalanche Warning.
A Special Avalanche Bulletin (which is what was issued on Dec. 14) is used when "dangerous avalanche conditions are expected in combination with a lot of people in the mountains," the avalanche center said.
If dangerous avalanche conditions are expected in the next 24-48 hours, an Avalanche Watch is issued.
Avalanche Watches are usually followed by Avalanche Warnings, the center said. Warnings are issued when there are "currently very dangerous avalanche conditions, and travel in avalanche terrain is not recommended, or should be avoided entirely."
Special Announcements are used to inform the public about avalanche closures from UDOT, ski areas, and other "pertinent events that people might find interesting."