Information update for March 30

This is Steve Karkanen with an information update on the recent avalanche accident near Superior, MT and updated backcountry avalanche conditions from the West Central Montana Avalanche Center for Wednesday, March 31, 2010.

Avalanche Accident

On Saturday March 27, a 29 year snowmobiler from St Maries, Idaho died in an avalanche accident near Missoula Lake on the Superior Ranger District of the Lolo National Forest. This area is on the MT/ID border 10 air miles SW from Superior, MT. The individual was riding down a steep chute at the end of a day of climbing when the slab released. He was caught and carried for an estimated 800 feet, was strained through trees and completely buried (about 4 feet deep) in a terrain trap. His partners were in a safe location, witnessed the avalanche and quickly located their friend with transceivers and dug him up. He died from his injuries shortly after he was dug up.

Investigators from the West Central Montana Avalanche Center on the Lolo National Forest went to the site Sunday to document the accident.

Initial indications are that this was a wet slab avalanche that released on a bed surface of surface hoar and small grained facets that formed several weeks ago. The avalanche was on a 6200′ NW aspect and was triggered at about 6PM so the slope would have had direct sun on it for a few hours. Temperatures at the nearby Hoodoo Basin SNOTEL (at 6050′) reached 41 degrees Saturday. The crown was estimated to be about 2 – 2.5 feet deep and 300-400 feet across. This avalanche is classified as WS-AM-R3-D3-O.

A more detailed report will be posted here and on avalanche.org after the investigation team interviews witnesses and completes their investigation.

Our thoughts are with his family and friends during this difficult time.

Current Avalanche Danger

It’s tough for us to assign a danger rating when we called it a season last week and observers have not been out but based on the information from the investigation team and the obvious heavy load much of our area just received I can easily suggest that the current avalanche danger is CONSIDERABLE and possibly HIGH on some slopes. Northerly facing slopes that have not been through melt freeze cycles will be the most dangerous as they are cooler and are allowing the deeply buried weak layer to persist even during the warm weather recently experienced here.

I wouldn’t trust anything steeper than 30 degrees on these slopes. Many areas received rain and that is never good for stability.

We’re starting to hear about avalanches involving the new snow and we received a great report and a photo of a large slab avalanche on a NE facing slope above 8000 feet near Downing Mountain. You can see the picture on our 2010 photo gallery.

Weather and Snowpack Analysis

Bitterroot Mountain SNOTEL sites are showing significant moisture in the form of rain and snow the past 48 hours. Since Sunday night, when the storm first entered the area, the Hoodoo Basin SNOTEL recorded 3 inches of snow water equivalent or about 19 inches of heavy wet snow. Hoodoo appears to have been the bulls-eye for the storm passage as sites to the north and south recorded much less moisture but still enough to be a problem.

The accident at Missoula Lake happened Saturday on a sunny day prior to the current storm cycle and involved the buried surface hoar layer we have been describing for several weeks. Lookout and Lolo Pass SNOTEL sites recorded about an inch of SWE but little new snow, maybe a couple of inches. The weight of the water is what we are concerned about. As far as the area around Hoodoo, which is about 6 miles south of the accident site, 3 inches of SWE is HUGE. We had an avalanche on Saturday prior to the storm, you can bet that conditions are even more unstable with that amount of weight dropped onto what has been a sensitive layer for several weeks now. It needs time to adjust.

Other SNOTEL sites report 48 hour storm total as follows:
North Fork Jocko: SWE 1.1 inches, new snow 6 inches.
Stuart Peak: SWE 1.7 inches, new snow 7 inches.
Saddle Mountain: SWE .30 inches, new snow 2 inches.
Twin Lakes: SWE 1.9 inches, new snow 8 inches.
Savage Pass: SWE 1.5 inches, new snow 10 inches.
Lolo Pass: SWE .90 inches, new snow 2 inches.
Lookout Pass: SWE .50 inches, new snow 1 inch.

I talked with a group of snowmobilers who were in the Surveyor Lake area Monday who reported rotten snow conditions down low and once they got enough elevation where it was snowing, conditions were tough with high winds with poor visibility. They reported seeing a large natural avalanche on an open northeast to east facing bowl in the area of Irish Basin. So they came home.

While we welcome the added snow, it comes on the heels of a terrible accident in the general area that involved the aforementioned buried surface hoar layer before the added weight of the storm just passed.

If you can’t stand it and need to go, please look for this weak layer before you commit to anything steep.

We still see a lot of variability of the snowpack structure in Western Montana and the surface hoar layer we’ve been concerned about just keeps hanging in there. It remains important to look for this weakness especially after any new snowfall.

Weather Forecast and Avalanche Outlook

The National Weather Service Office in Missoula is forecasting another round of afternoon snow showers but with little accumulation.

Expect dangerous conditions on the steeper terrain. As temperatures warm, expect to see many point release avalanches on steeper slopes in areas that receive significant snowfall amounts.

Last Friday was our final regular advisory of the season. We will issue information statements or advisories if needed depending on weather and snow conditions during the next few weeks. Many of our observers have returned to their other important duties or simply can no longer access the terrain they frequent during the course of the winter. If you get out and find conditions worthy of passing along, please do contact us at [email protected] or call our office number at 406-530-9766.