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Logan area Avalanche advisory

Tuesday March 13, 2007:

Hello, this is Toby Weed of the Forest Service Utah Avalanche Center with your Logan Area backcountry avalanche and mountain weather advisory.  Itís Tuesday March 13th, and itís 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 Avalanchetools.com.

Current Conditions:

Backcountry snow conditions are suffering from a few days of unseasonably warm temperatures in the mountains.  Upper layers of the snowpack are saturated on most slopes and at all elevations.  The snow on shallow lower elevation slopes is isothermal, soaked through and through, and lacking any semblance of structure is also very weak.  Lower elevation trails and roads melted out, and mud at the trailheads and the first couple miles of your approach may fowl up your day.  We found somewhat dry and fun soft snow on the north-facing bed surface of a large natural avalanche at ~9400í which occurred during the storm two weeks ago, but even the darkest shadiest north facing slopes where starting to get pretty sloppy by afternoon. Wednesday will be mostly cloudy and warm in the morning, with clouds decreasing and temperatures dropping a bit in the afternoon.

Avalanche Conditions:

Iím uncomfortable with these searing temperatures and the poor snow structure on many slopes.  Wet loose and slab avalanches are the most obvious concern, but large dry slab avalanches are also possible as the heat increases the creep rate of slabs overlaying old weak snow.  We have reports of a few significant human triggered slab avalanches from Tuesday in the Central Wasatch Range, including a couple close calls with potentially deadly avalanches stepping down into old weak snow.  Skiers sympathetically triggered two slab avalanches on a south facing slope across the road from Alta, and a skier triggered a large dryer hard slab avalanche on a north facing slope at around 10,000í near Brighton. Today I noticed several fresh looking slab avalanches on steep upper elevation slopes in the Mount Naomi Wilderness and lots and lots of evidence of recent wet loose avalanches, mostly on steep slopes facing east or west.

Despite a gradual cooling trend, wet avalanches will still be a problem on Wednesday.  Iíll feel better about things after nighttime temperatures drop well below freezing for several hours.  Warm temperatures are quickly melting lower and mid-elevation snow and turning most slopes in the region very slushy.  The warmth is deforming cornices and some have been failing, putting a good wallop on any slopes below. Wet avalanches are possible on steep slopes at all elevations with saturated surface snow.  In some areas, a wet avalanche overrunning a steep slope with persistent buried weak layers could cause a deeper, potentially deadly hard slab release.

There are some areas where you still might be able to trigger deep and dangerous hard slab avalanches, and the heat in the past two days may have exacerbated the problem.  Iíd be most concerned in areas with a shallow overall snowpack and therefore very weak early season snow.  Rocky, wind-swept or exposed terrain at upper elevations is suspect, especially on slopes exposed to prolonged sunshine.  On many upper elevation slopes Februaryís slab is so thick that it would be difficult for a person to trigger an avalanche unless from a shallow part of the slab.  But, with the hot temperatures the slab is creeping faster than underlying layers, and significant natural avalanches may result.  Also, the once hard slab may have been softened by the heat and a slab which may have easily supported your weight last week may now be sensitive to your presence on a slope.  In these conditions itís wise to keep in mind that the weight of a smaller avalanche overrunning some slopes might be enough to trigger a deeper and much more dangerous hard slab avalanche running on deeply buried persistent weak layers.

Bottom Line:

There is a CONSIDERABLE danger and wet avalanches are probable on many steep saturated slopes at all elevations in the backcountry.  Persistent slab avalanches are possible on some steep upper elevation slopes, and the problem may be worsened by the recent heat-wave.  Dangerous hard slab avalanches are most likely in areas with shallow overall snowpack, facing west through southeast, and above around 8000í in elevation.  Avoid and stay out from under slopes steeper than about 35 degrees, especially those with saturated surface snow. 

Mountain Weather:

A strong westerly flow aloft will be over the region through Wednesday.  A weak cold front will move overhead early on Wednesday, bringing a slight chance of a little snowfall and cooling temperatures.  A high pressure will build in again for the weekend, bringing more unseasonably warm days.

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 evening.  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.