Archived Advisory for Tue Feb 19 2008

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TUESDAY, FEBRUARY 19

Good morning. This is Doug Chabot with the Gallatin National Forest Avalanche Advisory issued on Tuesday, February 19th, at 7:30 a.m. Sweet Pea Landscaping, in cooperation with the Friends of the Avalanche Center, sponsor today’s advisory. This advisory does not apply to operating ski areas.

MOUNTAIN WEATHER

If you liked yesterday’s weather, you’ll love today because it’s an encore performance. There’s been no new snow in the last 24 hours and overnight temperatures only dropped to 20F with moderate winds blowing 20 mph out of the west. Today, sunny skies will dominate with temperatures climbing to the low 30s and ridgetop winds blowing 15-25 out of the west. We’re under the influence of a strong high pressure system which looks to last a few more days.

SNOWPACK AND AVALANCHE DISCUSSION

The Bridger Range:

Strong winds over the weekend created wind slabs in the Bridger Range. These slabs broke easily with ski cuts. Scott and his partner toured to Saddle Peak yesterday and found that the stability is getting better, but it’s not completely bomber on these slopes. At least not yet. A few more days of warm weather should do the trick of bonding these slabs to the layers underneath. Recently wind-loaded slopes have a MODERATE avalanche danger. All other slopes have a LOW danger.

The northern Gallatin and northern Madison Ranges:

The northern Gallatin and northern Madison Ranges still have weak snow near the ground that are producing clean shears in our stability tests, and even more telling, are avalanching with human triggers. An avalanche on Friday in Buck Ridge south of Big Sky caught some snowmobilers. Steep, wind-loaded terrain was the culprit. Additionally, we know that a layer of surface hoar is buried 6-8 inches deep on some slopes. Surface hoar is a notorious weak layer and could result in human-triggered slides on recently wind-loaded slopes. For today, the avalanche danger is CONSIDERABLE on wind-loaded slopes steeper than 35 degrees. A MODERATE avalanche danger exists on all other slopes.

The southern Madison and southern Gallatin Ranges, the Lionhead area near West Yellowstone, the mountains around Cooke City, and the Washburn Range:

Steep, wind-loaded slopes demand extra attention in our southern mountains. A group of us, including the GNF Snow Rangers, investigated a large avalanche on Skyline Ridge in the southern Madison Range yesterday. It ran 1500 feet and put deadly piles of debris 10-15 feet deep in the lower gullies. You could see rocks in the starting zone and the snow composition was very similar to the slide I looked at near Buck Ridge on Saturday. A 1-3 foot deep wind slab avalanched on a 2 foot thick layer of faceted snow. Exposed slopes above treeline seem to be especially susceptible to this slab, facet combination. In this area, recent northwest winds quickly loaded this south-facing slope.

YouTube of my investigation: http://www.youtube.com/watch?v=AF5ILCjHRIE

Some photos of the avalanche: http://www.mtavalanche.com/photos/photos.php

In Cooke City, wind-loaded slopes would be prone to human triggering too. This is especially true on south faces which have an ice crust shallowly buried. On a positive note, there are many stable slopes in our southern mountains. I found great riding outside Cooke City last week and yesterday skiers had stable, safe turns in steep terrain north of West Yellowstone. Staying clear of slopes with recent wind drifting is good practice any day of the year. For today, the avalanche danger remains CONSIDERABLE on recently wind-loaded slopes steeper than 35 degrees. All other slopes have a MODERATE danger.

KING AND QUEEN RESULTS

The King and Queen of the Ridge, held this past Saturday, was another huge success. Forty-two participants hiked the ridge at Bridger Bowl to raise money for avalanche education. John Parker reigned King his second time in 3 years with 26 hikes. Angela Patnode, an avalanche instructor for the Friends, was the Queen and earned her pay with 21 hikes. And Scott Schmidt just keeps getting fitter the older he gets. He pumped out 23 laps. I missed the event, and thankfully missed being crushed by Scott, because I investigated the avalanche on Buck Ridge that caught 5 folks. If you missed the video clip, here it is: http://www.youtube.com/watch?v=Thd5Vl7EPW4

I will issue the next advisory tomorrow morning at 7:30 a.m. If you get out in the backcountry give us a call or email with your observations. You can reach us at 587-6984 or email us at mtavalanche@gmail.com