In partnership with: Utah Division of State Parks and Recreation, The Friends of the Utah Avalanche Center, Utah Department of Emergency Services and Homeland Security and
“keeping you on top”
March 18, 2007 7:30 am
Good morning, this is Drew Hardesty with the
A SPECIAL AVALANCHE ADVISORY REMAINS IN
EFFECT FOR THE MOUNTAINS OF
Skies are clear with light westerly winds along the ridgetops with a few stations recording gusts into the low 20’s every now and then. More importantly, overnight lows dipped just to the upper 30’s and 40’s, with cooler air filtering down to the lower elevations. Any refreeze will be shallow and superficial in nature. Decent corn conditions exist on steep sunny aspects, but you may be too late if you haven’t left by now. High north still holds a few decent patches of soft settled powder.
Snow and Avalanche Discussion:
Explosive testing continues to produce impressive, yet spotty results. One 10 lb airblast on a steep upper elevation east-northeast aspect at one of the Park City resorts pulled out a wet slab 3’ deep and 100’ wide, ultimately stepping to the ground 6’ deep and 200’ wide. Other ski areas and the DOT crow-barred out a few wet slabs in the upper elevations but we didn’t hear about much in the backcountry.
In my experience, wet
slab avalanches can be the most difficult to forecast. It’s usually more about decreased strength of
the snowpack, rather than increased stress through rapid loading as we all know
and love for cold snow avalanches.
Supportable corn slab avalanches, particularly with remnant faceted
grains, may be the most devious of all. They’ll
support you like a hard slab until you collapse the crust, with it pulling out
above or adjacent to you, digging in to the wet grains what, 8-20” beneath
you. This week’s accident above
Well, what to do? First, avoid descents on the steep sun-exposed slopes during and just after the heat of the day. If you can get some snow moving with turns and you’re riding in the snow rather than on top of it, move to a more westerly aspect or around to the north. Plunge a ski or probe pole to see the depth of refreeze and depth altogether. Give more caution to those slopes with a thinner isothermal snowpack with a thinner refreeze. Recognize that cold snow avalanches with buried persistent weak layers can be a bit more sensitive. Regardless, it almost always comes down to timing and terrain. When thing start to fall apart, hug the ridges and sub-ridges, and avoid being above or in steep-walled terrain traps like these (525k for higher resolution).
Bottom Line for the
The avalanche danger is CONSIDERABLE today on and below slopes of about 35 degrees and steeper, and may rise to HIGH this afternoon as the day heats up. Slides can be triggered on steep slopes of all aspects and elevations, and both human triggered and natural avalanches are possible. A few of these slides have the potential to be very large, dangerous, and long running.
A weak, dry cold front may keep temps from fully spiraling out of control today, though we’ll still see mountain temps in the 40’s at 10,000’ and 50’s at 8000’. Winds will be light and westerly. Tomorrow the winds will shift to the southwest ahead of a splitting system on tap for Tuesday night. It should be enough to put 4-8” in the mountains as temps fall back to the upper teens.
The Wasatch Powderbird Guides flew avalanche control missions for Little Cottonwood DOT yesterday, and are unlikely to get out today. For more info, call 742-2800.
The UAC and ACE are offering a day long Women’s Avalanche Awareness class at Alta on March 22nd covering beacon use and basic safe travel, terrain and snowpack information, for $30. For more details go to: www.altaarts.org.
Listen to the
advisory. Try our new streaming audio or
UDOT highway avalanche control work info can be found HERE or by calling (801) 975-4838.
Our statewide tollfree line is 1-888-999-4019 (early morning, option 8).
For a list of avalanche classes, click HERE
For our classic text advisory click HERE.
To sign up for automated e-mails of our graphical advisory click HERE
We appreciate all the great snowpack and avalanche observations we’ve been getting, so keep leaving us messages at (801) 524-5304 or 1-800-662-4140, or email us at [email protected]. (Fax 801-524-6301)
The information in this advisory is from the U.S. Forest Service, which is solely responsible for its content. This advisory describes general avalanche conditions and local variations always occur.
I will update this advisory by 7:30 on Monday morning, and thanks for calling.