Feb 21, 2014 @ 6:47 am

Avalanche Advisory for February 21, 2014

The avalanche danger remains HIGH on all wind loaded terrain steeper than 30 degrees.  Natural avalanches are likely, human triggered avalanches very likely.

On other steep terrain, the avalanche danger is CONSIDERABLE.  Natural avalanches are possible, human triggered avalanches are probable.

The HIGH avalanche danger is in all mountain locations above 5000 feet in the Bitterroot Mountains from the Lost Horse Drainage/Twin Lakes area to Hoodoo Pass, the Rattlesnake Mountains and the southern Swan and Mission Mountains on National Forest System lands near Seeley Lake, MT.

The southern portion of our advisory area near Lost Trail Pass/ Saddle Mountain has not received as much precipitation the past 24 hours and observers felt that stability has improved.  In this area, the avalanche danger is CONSIDERABLE on recently wind loaded terrain steeper than 30 degrees.  The main avalanche problem in this area is storm snow and wind slabs on the steeper terrain.

Hello!  This is Steve Karkanen with the Friday avalanche advisory from the West Central Montana Avalanche Center.  This information is the responsibility of the Forest Service and does not apply to operating ski areas.  The danger rating expires at midnight tonight.


Weather and Snowpack

The western Montana mountains continue to be influenced by vigorous winter weather. Copious snowfall amounts have given us some of the best skiing and snowmobiling opportunities of the winter, but it has also made snowpack conditions dangerous in many areas.

This morning, SNOTEL data indicates about a foot of new snow with mountain temperatures in the low twenties.  Wind speeds are a problematic 30 mph from the WNW with gusts to 45 mph at Point Six. At Deer Mountain east of Darby, 7200 foot winds are lighter from the SW at around 10 mph gusting to 32 mph.

Information from our field observers and avalanche specialists indicate that conditions will likely worsen with more snow and wind.

In the Rattlesnake, Travis and his partner found fresh wind slabs on multiple aspects and experienced localized collapsing and whumpfing while traveling on low angle terrain.  They reported that these new wind slabs were failing easily with energy on small test slopes.  Their pit stability scores were a bit more disconcerting. On north aspects the buried facet layer failed and propagated with a score of ECTP23 and a CT score of 17 Q1 on south aspects. East aspects have more snow but some areas have deeply buried facets that can’t be trusted.

A report from Yurt Ski in the southern Swan indicates similar conditions as the Rattlesnake with the buried January facet layer getting reactive with the additional snowfall this week.

In the southern Bitterroot, Ed and Casey report a stronger snowpack than in the northern portions of the range near Lolo Pass but felt that heavy new snowfall will increase the possibility of higher consequence deep slab failures. The primary avalanche problem in this area is the recent storm snow slabs that have not yet had the time to bond to the older snow interfaces. Another concern is the potential for these slabs to fail then possibly step down to the more deeply buried faceted layers that formed in January. Cornices are getting huge and failing on their own throughout the area.

John at Downing Mountain Lodge also reports excellent skiing conditions with no visual or audible signs of instability.

High wind and heavy snow hammered the areas surrounding Lolo Pass all week.  Dudley and Tim feel that additional new snow and wind is keeping the avalanche danger elevated with wind and storm slabs as the primary avalanche problem with a possibility of triggering the persistent slab now several feet deep into the pack.

We did not receive any information from the Hoodoo Pass area this week.  The Hoodoo SNOTEL is reporting 3.2″ of SWE since February 18, well over 30″ of new snow .

While recreation conditions now are epic, you must consider that many areas harbor a dragon and can’t be trusted. Heavy new snowfall on steep terrain will be the most obvious problem this weekend, but the hidden danger doesn’t give us any obvious clue as to it’s whereabouts or temperament.

This is a low probability/high consequence problem that is making it difficult to predict with any degree of certainty. What we can tell you is that it is a factor to be reckoned with. It is a widespread condition that has healed up in many locations. It wasn’t much of an issue earlier this month but has recently become more reactive with the heavy load we received last weekend.  The avalanche in the Spruce Creek area near Lolo Pass/Beaver Ridge area is a prime example of what we’re dealing with.


Weather and Avalanche Forecast

The Missoula Office of the National Weather Service has issued a winter storm warning for our area. Snow banding is causing snowfall rates of 2-3″ an hour in many mountain locations this morning. 6-8″ of storm snow is possible in the mountains with 3-6″ in valley locations.  A more significant winter storm is forecast to enter into western Montana Sunday with high winds and heavier snowfall amounts than the current system.

I expect the avalanche danger to worsen if this system delivers as forecasted.


Bitterroot Level 1 Avalanche Class

This class has a few more open slots so if you are undecided, consider that there is no better time to take an avalanche class than during dangerous avalanche conditions.  It will be a great opportunity to enhance your snow assessment skills and learn risk management practices in conditions that are perfect for practicing what you learn.  To register contact the U of M Outdoor Program Office at 406-243-5172.

I will post the next regular avalanche advisory Tuesday, February 25.  Please enjoy a safe weekend!





This information is the sole responsibility of the Forest Service and does not apply to operating ski areas. The avalanche danger rating expires at midnight tonight but the information can help you make a more informed decision regarding travel in avalanche terrain for the next few days.

Our advisory area includes National Forest System lands in the Bitterroot Mountains from Lost Trail Pass north to Granite Pass, the Rattlesnake Mountains north of Missoula and the Southern Swan and Mission Mountains near Seeley Lake, MT. Avalanche information for the Lookout Pass/St. Regis Basin area is available from the Idaho Panhandle Avalanche Center.