Feb 1, 2013 @ 6:16 am

February 1, 2013 Avalanche Advisory

The avalanche danger is MODERATE above 5000 feet in the west central Montana mountains. Heightened avalanche conditions on specific terrain
features. Evaluate snow and terrain carefully; identify features of concern.

Good Morning. This is Tim Laroche with the West Central Montana Avalanche Center’s backcountry avalanche advisory for Friday, February 1st, 2013.


Weather and Snowpack Analysis

All advisory area locations continue to receive snow. Most areas received 3-6 inches of new snow in the past 24 hours which means 2.5+ feet of snow this past week. Winds have been blowing steady from the west and southwest 15-20mph since Monday. Temperatures have been in the upper 20’s and low 30’s. Currently, the winds have calmed, temperatures are in the upper 20’s to low 30’s, and it’s snowing.

The main avalanche concern is fresh wind slabs that have formed on upper elevation ridgelines throughout our advisory area. These drifts are 2-3 feet deep. They are mostly found on north through southeast aspects. They can be stubborn and may break further above you than you might expect. Avoid steep slopes where these drifts have formed.

The secondary avalanche concern is storm snow avalanches. Temperatures have warmed as we have continued to receive copious amounts of new snow. Although this has allowed the snow to settle and bond to the old snow surface, there are density changes in the new snow that are still weak. On our tours, we experienced only localized collapsing and cracking, but you will want to pay attention to how the snow reacts when you commit to a steep slope.

Beyond the 2 primary concerns, there are 3 other things to pay attention to.

  1. The surface hoar layer that formed in mid- January in the Bitterroot Mountains (photo) is now buried 2-3 feet deep and has been moderately reactive in some stability tests (profile).
  2. Below the elevation of 6000 feet, we have been getting rain on snow. Watch for heavy, wet point releases in these areas.
  3. A slick rime crust formed in the upper part of the snowpack on Wednesday morning. This only has a few inches of snow on it right now, but has created a very weak layer and will not support a new load of snow.


Weather Forecast and Avalanche Outlook

Snow continues this morning as the northwest flow persists over our area. Expect 1-3 inches of new snow this morning before drier air pushes in from the west. Temperatures will be in the mid 30’s and winds will be light out of the west.

I expect the avalanche danger to decrease as precipitation comes to an end and the snowpack has time to settle and adjust.

Steve will issue the next advisory on Tuesday, February 5th.

Additional Safety Information:

An interesting YouTube clip that reinforces the reason why ALL electronic devices (cell phones, radios, GPS units, etc) must be turned OFF when conducting a search.

If you get out and have the time to send us some information about what you are seeing, please use our “public observations” link on our website or send us a quick note at [email protected]. Thank you for your continued support!





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.