Wasatch-Cache National Forest:  In partnership with:  Utah State Parks and Recreation, Friends of the Utah Avalanche Center-Logan, and Utah State University College of Natural Resources.


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Logan area Avalanche advisory

Tuesday March 20, 2007

Hello, this is Toby Weed of the Forest Service Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  It’s Tuesday March 20th, and it’s 9:30 in the evening.  This advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Import Auto.

Current Conditions:

The prolonged heat-wave burned off many lower elevation slopes, but there’s still a lot of snow up high.  The Tony Grove Snotel still reports 5 feet of total snow on the ground and 70% of average water content for the date. Thankfully, mountain temperatures are forecast to fall drastically overnight with the arrival of colder air courtesy of a splitting Northern Pacific spring storm.  Temperatures should drop into the upper teens for several hours at 9000’. We are also likely to pick up 6 to 8 inches of snow in favored upper elevation areas, and there’s hope for fairly nice shallow powder conditions on Wednesday. You may have to cross some melted-out barren ground on your way up through the lower elevations, so be mindful, stay on route, and try to limit potential resource damage. 

Avalanche Conditions:

Wet loose and slab avalanches were common across the region over the weekend, but cooler temperatures today probably settled things down a little.  From lower Logan Canyon on Sunday afternoon I noticed two large wet avalanches on northerly facing slopes high above Third Dam. If you look into upper Spring Hollow, you can clearly see an avalanche under a large and prominent cliff band at around 8400’ in elevation.  The other is in a path called Drop In-Drop Out, a hanging gully above Zanavoo very visible south and east of Third Dam (photos).  The wet slides gouged down into moist rotten snow near the ground, entrained tons of heavy wet snow, and were generally significant avalanches. 

Even though it’ll be much cooler on Wednesday, wet avalanches will still be possible on lots of steep slopes in the region.  The refreeze will not have been long-lived enough to solidify suspect deeply buried persistent weak layers that have been moistened and made weaker by melt water that made its way down through the snowpack during the heat-wave. You might trigger wet slab or partially refrozen slab avalanches (“corn slabs”) on some steep slopes, especially on slopes which absorbed lots of solar heat during the recent warm spell.  Watch out for slopes with moist and un-cohesive basal snow or depth hoar near the ground.  Sunny slopes at higher elevations with shallow overall snow cover are the most suspect.  In spite of the cooling, a few spontaneous glide avalanches, where the entire snowpack slowly slides along the ground until it releases, are also possible in some steep sunny areas with smooth ground or rock slab underlying surfaces.  These often occur during the initial drop in temperatures after a prolonged warn spell and are possible at any time of day or night.  Obviously, you should stay out from under suspect steep slopes and obvious glide cracks, which have opened up on some slopes in the past couple days.

The forecast 15 to 20 mph northwesterly ridge top winds will be strong enough to build drifts and sensitive soft slabs on lee slopes near ridge lines and around exposed terrain features.  As usual you should avoid fresh drifts on steep slopes.  These are generally made up of stiffer snow, often sport a chalky appearance, and can sound kind of hollow as you pass over them.  I recommend digging down to the interface of the old and new snow and testing the bond between the two layers.  Sometimes a drastic temperature difference or particular crust formation can lead to a weak bond leading to increased wind slab sensitivity and/or storm snow soft slab activity.  More snow or stronger wind than forecast will create larger potential avalanches.  

Bottom Line:

There’s a MODERATE danger in the backcountry, and triggered wet and wind slab avalanches are possible on steep slopes in the region. You’ll find freshly formed wind slabs consisting of tonight’s new snow in exposed terrain at upper elevations, most likely on slopes facing north through southeast.  A lingering danger of wet avalanches can be found on any slope with substantial snow cover and moist un-consolidated basal layers. Wet slab and isolated spontaneous natural glide avalanches are most likely on upper elevation slopes facing northeast through south, which absorbed lots of solar heat in the last week.  Use good snow assessment and safe travel techniques to minimize risks.

 Mountain Weather:

The storm is here and rain is falling in Logan. 6 to 8 inches of snowfall is possible at upper elevations by mid-morning.  More importantly, mountain temperatures are expected to drop well below freezing with frontal passage and stay cool for the balance of the work week.  High pressure will build back in over the weekend with more fair weather in store. 

General Information:

Check out photos of last week's avalanches in the Logan Area on our images page.

Go to the Avalanche Encyclopedia if you have any questions about terms I use in the advisory.  I also recommend the recently-released Media Page, which shows the forecast danger for our coverage areas across the state.

Please e-mail me at [email protected] or leave me a message at 755-3638 if you see or trigger avalanches in the backcountry.  The information you provide may save lives...

 This advisory will expire on Wednesday night. I will update it again on Thursday evening.

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.