Avalanche Advisory for February 4, 2014

The avalanche danger is CONSIDERABLE on terrain steeper than 35 degrees above 5000 feet in the west central Montana backcountry. Dangerous avalanche conditions exist, natural avalanches are possible and human-triggered avalanches are likely.

On all other terrain, the avalanche danger is MODERATE.  Natural avalanches are unlikely but human-triggered avalanches are possible.

Good morning!  This is Steve Karkanen with the February 4, 2014 avalanche advisory from the West Central Montana Avalanche Center.  The avalanche danger rating expires at midnight on February 4th and does not apply to operating ski areas.

 

Weather and Snowpack

SNOTEL stations picked up a few inches of new snow with winds mostly from the west gusting into the 30 mph range since Friday.

This morning SNOTEL stations report a a trace of fresh snow with temperatures in the negative teens.  At Point Six, the temperature at 5 am is -18 F and an east wind is gusting to 41 mph.  The wind chill is  -49 degree F!

We received several reports the past few days from a variety of locations.  Most sources suggest overall stable conditions with a few outlier human-triggered avalanches reported to us. We received a good report of a skier triggered avalanche near Lost Trail Ski Area on Friday then on Sunday, a snowmobiler triggered an avalanche near Beaver Ridge (Lolo Pass) and was able to ride it out.  Both avalanches were on steep north facing terrain near 7000 feet and failed about 2 feet deep at the interface of the past weeks snowfall on facets that formed during the late January dry spell.

No one was injured or buried in these small avalanches but they do remind us of the possibility of triggering an avalanche if the right spot is disturbed.

Dudley and Travis were touring the Rattlesnake Monday and noted several areas where recently formed wind slabs failed about 12 inches deep on steep north to northeast aspects sometime early Monday morning. They also noted localized collapsing and fracture propagation while they moved around on the snow surface.

Recent wind slab formations and loose storm snow on open terrain steeper than 35 degrees are the main avalanche problems today.  We’re hearing about and finding many places where the new snow fails easily on the faceted surface that formed in late January and at a density change within the newest storm snow.

Although the surface hoar was destroyed in most locations and the most recent storm snow is settling and bonding to the January surface, you don’t want to blindly trust every slope. The two avalanches reported to us Monday are enough evidence to support this.

Another avalanche problem that can not be discounted is the now deeply buried faceted layer near the ground. This condition has healed well with time and snow but we still find it in shallow snow, in rocky areas and on steep heavily shaded north facing terrain. You have to dig around and conduct stability tests to rule it out.

 

Weather and Avalanche Forecast

According to Missoula Weather Service Office forecasters, we can expect a bitterly cold arctic air mass to push through the northern Rockies with 30-40 mph easterly winds and light snowfall during the next couple of days.  Snow and blowing snow will reduce visibility and increase the wind chill especially near the mountain passes. Backcountry users need to be prepared for these dangerous wind chils for the next few days.

We don’t expect much in the way of new snow for the next couple of days but the recent storm snow is getting moved onto a variety of aspects by the high winds. I expect the avalanche danger to remain CONSIDERABLE (dangerous) until the wind and temperatures start to moderate later in the week. Heavy new snowfall and wind will worsen the avalanche danger particularly on wind drifted slopes.

Cold temperatures this week will allow weak layers to persist for a few more days, maybe even weeks in some areas. The interface of the late January dry spell and the  storm that began on January 29th is the main layer of concern. This photo of the buried surface hoar layer illustrates what to look for for the next few weeks.  This situation is isolated and can be found in pockets sheltered from the wind. Notice that this profile is on flat ground in a place that is protected from prevailing winds.

While it seems that we have a complicated snowpack with buried facets in some places but can’t find it in others, stable conditions here and maybe not as stable there, it’s really not that complicated.  But you have to conduct your own assessment to be certain. Absorb everything, ignore nothing.

Recent avalanches, heavy new snowfall, high winds, collapsing snowpack and a known weak structure buried about two feet deep is all the hard data you need to determine that it is probably NOT a good idea to ride or ski onto steep open terrain for a few more days. Sure, the chances are good that you can get away with it, but is it really worth dying for.

We’ve received several excellent reports from many different locations recently. These observations are valuable for the entire community.  They help us formulate a better avalanche advisory and help others make more informed decisions while recreating in avalanche terrain.

You can send information to us in many ways.  You can fill out and submit our on-line observation form here or you can send us a quick email at [email protected]  You can also leave a voice mail at 406-329-3752.

I will issue the next advisory this Friday, February 7.  Stay warm and be safe out there!