Avalanche Advisory – 3/5/2014

ISSUED ON March 5 2014 at 7:00 am.

The Flathead Avalanche Center is issuing a Backcountry Avalanche Warning for the entire advisory area including the Whitefish Range, Swan Range, Flathead Range, and portions of Glacier National Park. New snow, rising temperatures and snow levels, and strong winds have created highly unstable conditions. Natural and human triggered avalanches are likely.The avalanche danger is rated HIGH on all slopes in our advisory area. Very dangerous avalanche conditions exist. Travel in avalanche terrain is not recommended and avalanche runout zones should be avoided.

This warning will either be allowed to expire or updated by 7:00 a.m. on Wednesday, March 5.

Good morning! This is Todd Hannan with the Flathead Avalanche Center avalanche advisory for Wednesday, March 5, 2014. This advisory applies only to backcountry areas outside established ski area boundaries. The next scheduled advisory will be Saturday, March 8, 2014.


MOUNTAIN WEATHER

WeatherGraphicIn the past 24 we received an additional .3-1.4 inches of snow water equivalent. Snowfall amounts are only 2-7 inches. The snowfall measurements can be deceiving as snow has become increasingly heavy since the onset of the storm and settles underlying lower density snow as it falls. Currently temperatures are 27- 34°F and winds range from 5mph up to 25 mph out of the southwest. For today expect light snow showers this morning increasing midday and becoming heavy at times. Snow levels should continue to rise, we could see rain up to 5000 feet today. Southwest winds are expected to increase late morning to 10-25 mph.

 


RECENT OBSERVATIONS

RecentObservationsGraphicYesterday were in the Cascade/Rescue Creek drainages in the Flathead Range. On our ascent we noted that the top 2-3 inches of snow was affected by the rise in temperature and had become moist. The moist snow surface was present to about 5000 feet then transitioned to a dry graupel surface. While ascending the ridge we noticed that the top 6 inches of snow was denser than underlying snow and cracked around our skis when traveling over it. The light was flat and visibility was not great, but we were able to see debris and evidence of recent avalanche activity in the lower paths and run outs in the Rescue drainage. Extended column tests revealed 2 layers that were capable of propagating a fracture. One failure occurred with moderate force on a density change within recent storm snow 1.5 feet down (ECTP 13) and the other propagated with hard force in lower density snow on top of a melt-freeze crust 2 feet down (ECTP21 and 23) (photo). On our decent we experienced a collapse and long shooting cracks on a low angle slope. At 4400 feet, light snow was transitioning to a rain/snow mix and became all rain just below that. Large pinwheels were forming from snow coming off of our skis onto steeper slopes below (photo). On open slopes these pinwheels triggered loose, wet avalanches. The wet snow was confined to the top 2-3 inches of the snowpack and snow remained dry below that (photo). We experienced several more audible collapses in the snowpack at low elevations, proving that the underlying low density snow was struggling to support the load above.

General storm snow profile. Rescue Creek 3/4/2014

General storm snow profile. Rescue Creek 3/4/2014

Light rain began in the afternoon below 4400 feet. Dry low density snow will have difficulty supporting wet snow above. Cascade Creek 3/5/2014

Light rain began in the afternoon below 4400 feet. Dry low density snow will have difficulty supporting wet snow above. Cascade Creek 3/5/2014

Pinwheels starting to form from snow off of our skis. Cascade Creek 3/4/2014

Pinwheels starting to form from snow off of our skis. Cascade Creek 3/4/2014

 

 

 

 

 

 

 

 

 


SNOWPACK DISCUSSION

Avalanche Problem #1

Storm SnowOver the past few days we have seen a substantial amount of weight added to the snowpack. Short lulls in precipitation have not been sufficient to allow for adjustment to the load. Since the onset of the storm on Sunday, temperatures have warmed, piling heavier more dense snow on top of colder lower density snow. In addition to new snow that recently fell, there have been winds capable of transporting snow and loading leeward slopes with an even heavier burden. The snowpack is providing us with obvious signs of instability such as natural avalanche activity, shooting cracks, and collapsing. It is recommended to heed its warning and avoid avalanche terrain and run outs today.

 

 

 


Avalanche Problem #2

WetAvalGiven the rising snow levels today and increased potential for rain at even higher elevations, wet avalanches are a concern. We saw loose, wet avalanche activity yesterday and the potential will increase today. The collapsing we experienced at low elevation proves the potential for wet slab activity to occur. We could also begin to see renewed activity from glide cracks. At low elevations on roads or trails remember that even small avalanche paths and cut banks can produce dangerous avalanches. Avoid steep slopes and terrain traps such as gullies and narrow canyons when surface snow becomes wet, you observe pin wheels, or it is raining on the snow.

 


Avalanche Problem #3

Persistent SlabPersistent slab remains a concern, particularly as we stress them with a new load. The deep persistent slab on the mid-January crust with weak snow adjacent to the crust still poses a threat in many areas. Additionally, there have been several recent observations of layers of weak faceted snow buried 2-3 feet down from the surface. Once initiated, a persistent slab has the ability to propagate long distances, change aspects, and wrap around terrain features. Remain vigilant in assessing slopes for persistent slab instabilities and be aware of the potential for smaller avalanches to step down into these deeper layers and propagate longer distances. Identifying persistent slab is only half of the battle, be thinking of how and in what areas you might be able to trigger them. Continue to avoid areas where triggering these deeper slabs is more likely, such as steep convex rollovers and in areas with shallow snow often found in steep rocky terrain or scoured areas.

 

 

 

 


BOTTOM LINE

For today the avalanche hazard is rated HIGH. Continued precipitation with rising snow levels and temperatures, will cause very unstable conditions. This means that natural avalanches are likely and human triggered avalanches are very likely. Travel in avalanche terrain is not recommended. Flattop Mountain SNOTEL site, which is representative of the Flathead Range received an additional 1.4 inches of water weight in 24 hours bringing the storm total to 3.4 inches.

 

High 

 

 

 

 

 

 

 

 

 

 

 

 

 

Note: Once again, given this persistent slab problem, we need data/information. The accuracy of the avalanche advisory and our understanding of this persistent slab problem becomes much more robust when we have more information. Thus, observations from all of you are extremely valuable to us. Even it is just a simple email saying “Hey, we found good riding in Mountain Range X, and observed no signs of instability or recent avalanches”. This type of information is just as important as observations of avalanches. The observations need not be formal, and can remain anonymous. Don’t’ worry, we won’t give away your secret riding spot either. Call us at 406.261.9873 or email us at fac.admin@flatheadavalanche.org. Thanks for your help.

 


Community Avalanche Awareness Night!!! Join the new Friends of the Flathead Avalanche Center (FOFAC) for avalanche discussions followed by an opportunity to socialize with other winter backcountry enthusiasts.
March 6, 2014 (Thursday). 6:30 pm – 8:00 pm program and social afterwards. Moose Lodge, Whitefish. Details here.

New blog post by Ted Steiner about risk assessment in the backcountry here.

See recent snow profiles as well as snow profiles from the entire season here.

Join us March 14, 8:00 p.m. at Penco. We are working with the Flathead Snowmobile Association for the first in a series of motorized specific backcountry safety seminars. Details here.

Check out an interesting new research project that you can participate in about winter backcountry riding/snowmobiling and decision making from the Snow and Avalanche Lab at MSU. Details here.


Observations are extremely valuable to us. If you’ve been out in the backcountry, please drop us a line with your observations at fac.admin@flatheadavalanche.org or call 406.261.9873. Thanks!


DISCLAIMER

DisclaimerGraphic

This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires 24 hours after the posted time unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.