Posted:
Dec 31, 2013 @ 6:25 am

New Year’s Eve 2013 Avalanche Advisory

The avalanche danger in the west central Montana backcountry is MODERATE. It is possible to trigger an avalanche on slopes above 7000 feet that are wind-loaded and 35 degrees and steeper. Despite modest snow accumulations; westerly winds have loaded leeward slopes at higher elevations. In addition; shaded, northerly aspects above 7000 feet may harbor weak  layers that could fail with a new load of snow.

Good Morning, this is Dudley Improta with the West Central Montana avalanche advisory for New Year’s Eve, 2013. This danger rating does not apply to operating ski areas, and along with the year 2013, expires at midnight tonight. (Dec. 31).

 Weather and Snowpack Analysis

Mountain temperatures are quite warm this morning; in the mid-twenties to lower thirties. Winds at higher elevations are out of the west at 15 to 25 mph. It is snowing this morning; Snotel sites indicate the southern Swans and the Idaho border areas are getting the most accumulation. Snowfall is predicted to increase today. Be aware of changing conditions, with the accumulation of warm, heavier snow.

Even though we’ve only had a few inches of snow since Sunday, high elevation winds will not let up (Photo from 12/29/13). Wind slabs on leeward slopes are the main avalanche problem. Over the past few days winds have blown hard out the south, southwest, west, northwest and north. These multi-directional winds make it hard to predict where a slab might be hiding. Side loading on a high elevation slope or in a couloir or gulley is a possibility as well.

We’re seeing, and getting reports of, failures in the upper snowpack in stability tests (Pit Profile); mainly on surface hoar that formed in the last couple of weeks. Also, I do not trust facets that may exist towards the bottom of the pack on cold, higher elevation aspects where the snow is shallow. I’m not going to trust these shallow areas until we get some more snow and these layers prove they can bear the load.

Otherwise, daytime mountain temperatures in the high twenties have strengthened the snowpack; especially at lower elevations.

Weather Forecast and Avalanche Outlook

A system is delivering snow to the area today; possibly with warm temperatures. Although snow amounts might be modest, strong westerly winds will load leeward slopes and side-load gullies and couloirs.

I would expect the avalanche danger to escalate today with this weather system. Be aware of changing conditions when in the field.

High pressure is expected to build into the area Wednesday.

Advisory Area and Public Observations

We have changed the advisory area this year (see the box at the bottom). I remind you of this to make a point of clarification; we may post public observations from the surrounding region that are outside of the advisory area.

If you have time, we’d appreciate hearing from you. You can send us a report on avalanche or snow conditions by using our public observations form or sending us a quick note at [email protected] .

Have a happy New Year!

I will issue the next advisory on January 3, 2014.

READ FULL ADVISORY  

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.