There is MODERATE avalanche danger in the mountains of west central Montana.  Natural avalanches are unlikely, human triggered avalanches are possible.  Heightened avalanche conditions exist on some terrain features such as recently wind loaded upper elevation slopes steeper than 35 degrees and in areas where facetsAngular snow with poor bonding created from large temperature gradients within the snowpack. formed on the snow surface during the Martin Luther King holiday.

Good morning!  This is Steve Karkanen at the West Central Montana Avalanche Center with backcountry avalanche safety information for Tuesday February 5, 2013.

Weather and Snowpack

Advisory area SNOTEL sites recorded temperatures into the high thirties on Saturday and Sunday then cooled back into the mid twenties on Monday.  Most sites have received a trace of precipitation by this morning and temperatures are in the twenties.

Last weeks storm snow has settled and bonded to the old snow surface during the past few days.  Warm then cold temperatures locked up all but the more sheltered northerly aspects. We’re finding a mostly stable snowpack with wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. being the primary avalanche problem above 8000 feet.  West to northwest winds have been relentless and moved a lot of snow during and after the last storm.  These hard slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are stubborn but can do a lot of damage if you happen to triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . one.    

A secondary concern is a now deeply buried facet layer that continues to gain strength but fails cleanly in stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). tests when enough force is applied.  This is not a widespread problem and the spotty/random nature of these buried facetsAngular snow with poor bonding created from large temperature gradients within the snowpack. makes it difficult to predict where they may be an issue. The only way to know if a slope has these little surprises is to dig down and look for them.

Last Thursday’s rimeSupercooled water droplets that freeze to objects in exposed terrain, forming icy deposits on the windward side. Rime can also form on snowflakes as they fall through the sky, giving them a fuzzy appearence. event that left a thin ice crustA crust is a hard layer of snow where liquid water has refrozen into grain fabric. Crusts usually result from sun, rain or wind. now about 6 inches down appears to be breaking down and is not producing failures in stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). tests.

In places where wind scouring is keeping the snowpack thin, there is weak, faceted snowAngular snow with poor bonding created from large temperature gradients within the snowpack. at the ground.  These places tend to be on more west – southwest facing slopes and it’s a good idea to keep them in mind.  These thin pockets have the weakest structure of any snow and are the most sensitive to triggers.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting light to moderate mountain snowfall through Thursday.  Six to nine inches of snow is expected along with an increase in westerly winds above 6000 feet.  The avalanche danger is expected to remain MODERATE.  Be wary of wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers.A cohesive layer of snow formed when wind deposits snow onto leewardWind erodes snow from the windward (upwind) side of an obstacle and deposits snow on the leeward (downwind) side. Deposited snow looks smooth and rounded. You should always beware of recent deposits of wind drifted snow on steep slopes. terrain. Wind slabsA relatively cohesive snowpack layer. A layer of snow stronger than underlying layers. are often smooth and rounded and sometimes sound hollow. are often smooth and rounded and sometimes sound hollow. during periods of high wind and new snow.

Although we are again trending toward mostly stable conditions, there are enough land mines out there that require good situational awareness and safe habits.  Just because we’re skiing and riding on steep terrain doesn’t mean we can’t triggerA disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche .A disturbance that initiates fracture within the weak layer causing an avalanche . In 90 percent of avalanche accidents , the victim or someone in the victims party triggers the avalanche . an avalanche.  Only expose 1 person at a time, spread out when traveling uphill and evaluate each slope before committing.

I will post the next advisory on Friday, February 8.

We’ve been receiving excellent reports from some of you.  These are very helpful to us.  If you get out we appreciate hearing about the snow stabilityThe chance that an avalanche will not occur, relative to a given trigger (usually the weight of a human). conditions in the area you visit. Drop us a line at info@missoulaavalanche.org and tell us what you see or post your observations on our public observations page.

Avalanche Awareness Program in Hamilton Wednesday 7pm

Dudley Improta will present an avalanche awareness program for the Bitterroot Ridgerunners Snowmobile Club and Ravalli County Search and Rescue this Wednesday, Feb. 6,  at 7pm in the Ravalli County Search and Rescue Building, 2029 N. First St in Hamilton.  The public is welcome and there is no fee.