Jan 1, 2010 @ 12:00 am

New Years Day 2010 Avalanche Advisory

Happy New Year! This is Steve Karkanen at the West Central Montana Avalanche Center with backcountry avalanche information for the 2010 New Year.

Current Avalanche Danger

Above 6000 feet on all aspects, the avalanche danger is MODERATE with pockets of CONSIDERABLE avalanche danger on some terrain features where snow has covered anchors. Treat wind loaded leeward ridgelines and some cross-loaded terrain with rock outcrops and open bear grass slopes with caution.

Below 6000 feet, the avalanche danger is LOW.

Weather and Snowpack Analysis

SNOTEL locations have received only a few inches of snow the past 72 hours with temperatures in high teens and 20’s. We see a definite strengthening of our snowpack over time but we are very concerned about how much new weight it will be able to handle. All reporting locations are reporting much stronger stability test scores but when a failure occurs, they are deep, fast and clean at the level of the facets that formed during the cold weather in December.

Many locations in the Bitterroot are reporting a layer of surface hoar that formed earlier this week is buried 2 to 8 inches deep and is failing easily during stability testing. We did not see this surface hoar layer during our tour in the Rattlesnake.

Nearly all stability tests are indicating moderate stability but there are pockets where we see easy failures particularly on south aspects, in rocky areas and where the snow is still very shallow. We are not seeing the widespread collapse noise and fracture propagations we reported 2 weeks ago.

A fair amount of time has passed and our snowpack has slowly been gaining strength. Stability test scores are showing this but the problem is when the test area fails; it still fails with a lot of energy, is fast, clean and easily propagates.

This YouTube video is of a Rutschblock (score is 5) on a northeast aspect and shows a fast clean shear at the interface of the slab and the faceted snow that formed in early December.

Weather Forecast and Avalanche Outlook

The Missoula Office of the National Weather Service is forecasting that a warm Pacific storm system will be moving through the area Friday morning. Moisture and energy with a northwest flow will move in behind this system with a chance of accumulating snow across the central and northern Clearwater Mountains and Bitterroot Range through the weekend. Warm air Friday will reduce snow ratios so look for this snow to be heavy and wet. Cold air aloft will move in Saturday increasing snow ratios.

Avalanche conditions will slowly strengthen as we continue to receive small amounts of snow. It is going to take several weeks for the weakness at the base of the upper elevation snowpack to gain strength and these short bursts of snow are not enough to affect the weak layer deep within the pack. If our area receives significant snow of an inch or more of snow water equivalent (SWE), I would expect to see widespread avalanche activity on all aspects. Areas where the surface hoar was buried will be sensitive with any amount of new snow and wind loaded terrain will be very sensitive.

The next updated avalanche advisory is January 4, 2010.

We rely heavily on the many excellent observations people are sending us this winter. They help us produce a more accurate avalanche forecast since our resources are limited.

If you get out and see avalanche activity or want to send us quick snow observations, send us a note at [email protected] or call us at 406-530-9766. 530-9SNO.


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.