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Utah Avalanche Center in Logan

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Logan area Avalanche advisory

Saturday February 10, 2007:

  Hello, this is Toby Weed of the Forest Service Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  Itís Saturday February 10th, and itís 7:30 am.  This advisory is brought to you in part by the Friends of the Utah Avalanche Center in Logan with help from Voile USA.

Current Conditions:

  There is a bit of new snow at upper elevations, and you can find pretty nice dust-on-crust riding conditions in the backcountry.  The Tony Grove Snotel reported another 1/10th of an inch of water overnight, and a whopping 1/2 inch of water accumulated in the last 72 hrs.  With just over 4 feet on the ground, the station sits at 60% of average for the date.    I've noticed a few areas at lower elevations where folks spun their tracks through the moist surface glop into unconsolidated sugary snow all the way to the ground.   Up high with a few exceptions, (like in the trees), the crusty snow under a few inches of moist powder generally supports your weight.  With just a few more inches, you'll hardly  notice the highly variable and often breakable crust formed during this week's warm temperatures.   Snowfall will resume this afternoon at upper elevations, with rain continuing below about the 7000' elevation-line.  Southwest and westerly winds may strengthen for a time during the day, with high temperatures at 9000' forecast to be just below freezing.

Avalanche Conditions:

  The avalanche danger may rise quickly as new snow piles up this weekend, especially if the steady southwest winds continue during the periods of heavy snowfall forecast for the next couple days.  Today you might trigger fresh wind slab avalanches on steep drifted slopes in exposed upper elevation terrain.  These will generally be fairly small and controllable, with drifts in the one-foot-deep range.  But, as snowfall resumes and consistent west and southwest winds continue this weekend, I expect the drifts to grow substantially.  The continuing moist and warm weather pattern is likely to overload existing buried weaknesses at some point in some places.  Most slopes in the backcountry are afflicted with underlying very weak sugary or faceted snow.  In fact, the base layers in many areas are as rotten as I've seen in years and years.  A highly varied crust-sandwich, made up of January's widespread rime-crust and last week's sun-crust caps the depth hoar in many areas, and it may form a temporary bridge over the weakness.  This will present a lingering problem on slopes that don't avalanche, and a persistent buried weakness that will be susceptible to triggering will exist.

Bottom Line:

Today, with a rising danger you'll want to use good snow assessment and safe travel techniques to minimize risk.  There's a MODERATE avalanche danger in the backcountry, and triggered slab avalanches are possible on slopes steeper than around 35 degrees with recent deposits of wind deposited snow.   Heavy snowfall and constant west and southwest winds could cause the danger of wind slab and more dangerous, persistent slab avalanches to rise to CONSIDERABLE by late this afternoon or overnight.  This means human triggered avalanches will be probable on steep slopes with significant deposits of wind drifted snow, and some natural avalanches are possible.

Mountain Weather:

The moist southwesterly flow will continue through the weekend, and more snow is on the way for upper elevations. The next wave of storminess should arrive sometime this afternoon and continue through Sunday.  The rain/snow line will hover around 7000' today, but snow is likely down to the valley floors by tomorrow evening.  There is potential for significant accumulations in favored mountain areas tonight and tomorrow, with of an inch to 1.5 inches of additional water-weight possible. 

 General Information:

Check out the recently released Media Page, which shows the current and forecast danger for our coverage areas across the state.

 I will update this advisory again on Sunday morning.

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.

Thursd