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

Thursday December 20, 2007

Avalanche Warning:  High winds and heavy snowfall will create a HIGH avalanche danger in the backcountry.  Triggered and natural avalanches are probable.  Avoid steep slopes and avalanche run out zones.

Hello and good morning, this is Toby Weed of the Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  It’s Thursday December 20th and it’s about 7:30 in the morning.  This advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Avalanchetools.com.

             Current Conditions:

Yesterday’s inverted snowfall made for tough trail breaking and slow turning conditions.  The wind effected and moisture filled snow on the surface capped lighter snow and you’d sink to your shins with every step.  Expect more of the same today.  With a high avalanche danger at upper elevations, continuing strong southwesterly winds, and heavy snowfall you’ll want to stick to sheltered low angled or low elevation terrain. 

            Avalanche Conditions:

The heavy new snow is piling up on highly suspect weak faceted or sugary snow on many slopes.  Last week’s cold put a strong temperature gradient through the shallow snowpack causing rapid rates of water vapor sublimation.  As the water vapor moves upward though the snowpack, the individual snow grains are transformed into faceted crystals lacking cohesion.  In the Bear River Range, you can find large grained facets or depth hoar near the ground from October and November on upper elevation north facing slopes and small grained facets formed near the snow surface (or throughout the preexisting shallow snowpack) in the early December snow on most slopes.  Yesterday, the preexisting snow seemed crumbly, falling apart as I dug test pits like Mom’s cornbread.

Avalanches are probable today on slopes where significant new snow stacks up on preexisting weak snow.  The problem will be exacerbated by wind drifting, and winds accompanying periods of high precipitation rates will lead to extensive loading over large areas and well off ridge lines.  Yesterday, we noted periods when the snow appeared to fall in wind-driven sheets, rapidly accumulating in the usually sheltered bowl.  We backed off our intended line in fear of the very rapidly building slab.  Soft slab avalanches consisting of new snow in the 1 to 2 foot deep range are likely today.

In some cases the additional load from today’s heavy snow may be enough to cause a deeper release into old faceted or sugary snow from October and November on steep shady slopes at upper elevations. And, smaller wind drift or storm snow avalanches may have the potential to step down into old weak snow near the ground creating significantly larger and more dangerous avalanches.  Deeper slab avalanches up to 3’ deep are possible on some slopes. Pay attention to obvious signs of instability like recent avalanches on similar slopes, collapsing or woomphing noises, cracking, or hollow sounding snow, and be willing to reassess your route.

Bottom Line:

  There’s a HIGH avalanche danger in the backcountry today. Both triggered and natural avalanches are likely on many slopes steeper than about 35 degrees and above around 8000’ in elevation.  Avoid steep slopes and obvious avalanche paths or run-out zones.

Mountain Weather:

Strong southwesterly winds and heavy pre-frontal snowfall will persist through the morning hours.  Expect a short-lived break in the action this afternoon ahead of a strong cold front that will cross the region this evening.  Lightning, strong winds, much colder temperatures, and heavy snowfall are all in store for the frontal passage.  Upper elevations in the Bear River Range should pick up 18-20 additional inches before the storm moves off to the east on Friday. A brief high pressure will clear the skies and it’ll be quite cold on Friday night. The next system will graze by Northern Utah on Saturday night and Sunday and yet another nice looking storm is setting up for Christmas Eve.

General Information:

Check out photos of 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'm very interested to know what you're seeing out there.  Please e-mail observations to me at [email protected] or leave me a message at 755-3638, especially if you see or trigger an avalanche in the backcountry. We keep all observations confidential.

This advisory will expire in 24 hours from the posting time.

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.