Each party will need to make their own time- and site-specific avalanche hazard evaluations. As time passes avalanche and snow conditions may change, sometimes quite rapidly. Transition zones between hazards exist.
To get updates from the National Weather Service Missoula website consult the forecast discussion for twice daily updates. The map display allows for the latest forecast by clicking on a location on the map. As well, one can type in a lat/lon to get to a specific area and get a spot forecast. In adddition a zone forecast can be received by going to this link that may be helpful, Zone Area Forecast for West Glacier/Bob Marshall Region, MT.
This is the Last scheduled Advisory for 2012- 2013 Additional advisories will be posted if conditions warrant
Because of the general nature of this advisory, each party will need to make their own time- and site-specific avalanche hazard evaluations. This advisory best describes conditions at the time of it’s issuance. As time passes avalanche and snow conditions may change, sometimes quite rapidly. Elevation and geographic distinctions used are approximate and transition zones between hazards exist. This advisory does not apply to developed ski areas.
CURRENT DANGER RATING
Considerable during periods of rain on steep slopes until refreeze occurs.
After a refreeze has occurred
It has been over a week since most areas have seen freezing temperatures. A system moved in Thursday night that started to bring precipitation in the form of rain to all elevations. Gains overnight have ranged from .07 to .4 inches. This precipitation is expected to continue through the weekend with snow levels slowly dropping to around 3000 feet by Saturday night.
Observations Wednesday and Thursday were from Kimmerly Basin in the Whitefish Range and the Middle Fork. The lack of any substantial freezing for over a week, warm temperatures and sunny skies has created settlement and warmed the snowpack. A wet slab avalanche and a glide crack failure were reported up the Middle Fork on Southeast aspects and numerous loose wet avalanches have been observed in other areas. Some of the loose wet avalanches were triggered by cornices that are either calving or completely collapsing. Stress tests did not propagate. More glide cracks are being observed throughout the area. Backcountry users will need to make site and time specific evaluations for the areas they are in.
Precipitation is forecasted to continue through the weekend with temperatures cooling through the period. This will drop snow levels to near the valley floors by Saturday night and Sunday. Precipitation amounts, in the form of rain in most places, are expected to be in the neighborhood of a 1/4 inch on Friday. This rain, in addition to the rain received Thursday night, will further weaken the bonds in the snowpack. Be cautious and suspicious around any cornices and glide cracks. Avoid steep slopes and terrain traps until refreezing occurs and especially during times of substantial rainfall. Slides have the potential to go to the ground, especially in areas of shallow snowpack. Potential problems include Loose Wet Avalanches, Wet Slab Avalanches and Cornice Falls.
The avalanche hazard will be Considerable during times or rainfall through today. Natural avalanches are possible and human triggered avalanches are likely. During times of refreeze and on moderate angle slopes, the hazard will be Moderate. Human triggered avalanches are possible.
The avalanche hazard should decrease through the weekend as rain turns to snow at most elevations and refreeze occurs. Additional snow fall on the already settled snowpack should have less of an impact, especially with freezing temperatures. Look for rain and warm temperatures to decrease stability and freezing temperatures to increase stability.
This is the last, scheduled advisory for the 2012/2013 season. We will be monitoring conditions and update the advisory as conditions warrant. As always, backcountry users will need to make site specific evaluations for the areas they are in. After this weekend, the general avalanche danger should be low, but there will still be specific areas of higher hazard at times.
No video available
Cornice calving triggering a WL-NC-R3/D2-O (Wet Loose- Natural (cornice) triggered- ran most of the slide path/ could bury or injure a person- on old snow) Kimmerly Basin 4/4/13