Avalanche Warning above 6000 feet

An Avalanche warning remains in effect for the higher elevations in west central Montana.  Above 6000′ on leeward slopes steeper than 35 degrees the avalanche danger is HIGH.  Very dangerous avalanche conditions exist at higher elevations that received heavy snow and wind the past 2 days. Natural avalanches are likely, human triggered avalanches are very likely.  Locations that have not received significant precipitation have MODERATE  avalanche danger. Below 5000 feet the avalanche danger is LOW.

Good morning, this is Steve Karkanen at the West Central Montana Avalanche Center with the avalanche advisory for Friday December 30, 2011.

Weather and Snowpack Analysis

If you haven’t ventured out of the valleys you would think it’s March not the New Year.  A series of cold fronts blasted through the area this week bringing rain and warm temperatures to the valleys, more rain in the foothills and heavy snow above 6000 feet.  The amounts of snow are as varied as the terrain but the key factor in where it accumulates is the wind.  Strong wind moved a lot of snow onto leeward terrain during this event so even locations that received just a few inches of snow now have a dangerous slab sitting on a very weak snow structure.

Yesterday our observers were out in force and most accounts confirm widespread instability resulting from a heavy load onto a mix of buried facets.  The old snow that sat through the December dry spell recrystallized in many areas and really hasn’t been affected by the warmer temperatures.  To further complicate the problem there are also 2 distinct surface hoar layers that fail easily in stability testing.

The bottom line is that we now have a dangerous slab sitting on a very weak underlying structure wherever heavy snow and wind loaded steep slopes.

We received a report of a slab avalanche pulling out of a SE aspect near Point Six yesterday.  This is no surprise as I experienced a large collapse of the snowpack on a 20 degree slope as I approached my snowpit site.   Observers near Lookout Pass, Hoodoo Basin and Lost Trail Pass also reported localized collapsing and whoomping noises – strong indicators of instability.  A large slab pulled out of a E-NE slope in the St. Regis Basin and we also received two great photos from the Skalkaho area.  While the Skalkaho is outside our advisory area, it is close and all the pictures clearly demonstrate what we are concerned about.

All the above were in locations that picked up decent snowfall with high wind.  Other lower elevation sites such as Lolo Pass are not yet experiencing the level of instability but as snow accumulates in these areas I would expect similar conditions.

Weather Forecast and Avalanche Outlook

Another Pacific storm will bring moderate to heavy precipitation and gusty winds to our area Friday with fluctuating snow levels initially then cooler temperatures as the front passes. High pressure is expected to return on Sunday.

Expect this period of High Avalanche Danger to continue for the next day or two until the snow has a chance to adjust to the new load.  Many of the sites that were touchy yesterday will begin a slow healing process and may seem stronger as the tell-tail clues begin to vanish.  Don’t trust anything steep and loaded until you can prove it to be safe.  The consequences of getting caught in even a small slide can be traumatic when the snow hasn’t yet covered rocks, trees and other vegetation.

You can view snowpit profiles and photos on our photo gallery. We also have a few YouTube videos on our playlist, the most recent tells the story better than I can.

We have been getting some excellent pit profiles, photos and reports from many of you. They are very much appreciated and help us better inform you about conditions. You can use the form provided on the website or send us a note at [email protected].

I will issue the next advisory on Monday, January 2.  Be safe and Happy New Year!