MissoulaAvalanche.org

Avalanche Information for West Central Montana

March 2, 2012 Avalanche Advisory

Current Danger Rating is MODERATE

There is MODERATE avalanche danger above 5000 feet in most areas of the west central Montana backcountry. However, there is CONSIDERABLE avalanche danger on wind-loaded slopes steeper than 35 degrees in the northern Bitterroot mountains from Hoodoo Pass to Lookout Pass.

Observers in the Hoodoo and Lookout Pass areas reported natural slides that were deeper and more dense than the activity reported elsewhere. For this reason, the avalanche danger is rated CONSIDERABLE on all wind-loaded steep slopes.

Good Morning! This is Tim Laroche at the West Central Montana Avalanche Center with your backcountry avalanche advisory for Friday, March 2nd, 2012.

Weather and Snowpack Analysis

All advisory area locations received new snow the past couple of days. The Hoodoo Basin area received 10 inches (1.2”SWE) since Wednesday, while all other advisory area locations received 4-7 inches (.4-.9”SWE) of fresh snow. The winds blew steady mostly from the West and temperatures hovered in the low twenties during the day. Currently, winds are blowing out of the West and Northwest from 4-7mph and temperatures are in the mid to upper teens under mostly cloudy skies.

The sun and warm temperatures we experienced on Monday and Tuesday helped to settle and strengthen the snowpack. It also left a sun crust on all but true North facing slopes, which is where you will find a thin buried surface hoar layer that formed on Monday and Tuesday and got buried by the new snow on Leap Day. The new snow has already sluffed off the steeper slopes and has appeared to buckle in this area of the Rattlesnake mountains (photo), where the slope was not quite steep enough for the snow to slide, even though the slope angle was 37 degrees. Where the new snow has not released, expect it to sluff easily on steep slopes.

The main concerns are fresh wind drifts that have formed on leeward aspects, new snow instabilities, and the potential for triggering a stiff slab on the old buried surface hoar layer that formed in early February now down 1.5-2 feet below the snow surface. This weakness has been slowly strengthening and has been less reactive in stability tests lately. However, we have received some reports of failures in the moderate range on this weak layer and it would be wise to look for this weakness on the slope you plan to ride. It is mostly found on shaded aspects at upper elevations.

If the sun comes out and temperatures rise during the next few days, you will want to pay attention to how the snow is changing. Watch for dormant weak layers to become more reactive and for point release slides on solar aspects especially around steep rock outcrops.

Weather Forecast and Avalanche Outlook

We should see some light snow showers today but not much accumulation, temperatures in the mid to upper twenties and moderate winds out of the West. The next weather system moves in on Friday night and Saturday and should produce another round of snow in the 5-8 inch range. This system is forecasted to come in warm and for snow levels to rise to 4500 feet by Saturday night. Winds will increase with this system blowing from the West.

I expect the avalanche danger to increase if we get forecasted snow amounts with increasing temperatures.

I will issue the next advisory on Monday, March 5th.

If you get out and have the time to send us some information about what you are seeing, please use our “submit observation” link on our website or send us a quick note at info@missoulaavalanche.org. This information is invaluable to us and in turn comes back to you in the form of a better forecast.

 

 

 

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 you can use the information we provide to help you make more informed decisions regarding travel in avalanche terrain for the next few days.

Our advisory area includes the Bitterroot Mountains from Lost Trail Pass North to Hoodoo Pass, the Rattlesnake Mountains and the Southern Swan and Mission Mountains near Seeley Lake. Avalanche information for the Lookout Pass/St. Regis Basin is available from the Idaho Panhandle Avalanche Center.