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| 3.28.2008 |
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This is Janet Kellam of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Friday, March 28, 2008 at 7:30 am.
Idaho Department of Parks & Recreation in partnership with Idaho's Snowmobile License Plate Program & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Special Announcement:
People have been able to safely ski and ride some very steep slopes this past week. Don’t take this for granted and assume all slopes are safe. In the Galena area we continue to see human triggered slab avalanches on east facing slopes, a foot and ˝ deep, where the recent snow is poorly bonded to underlying crusts or sits on very weak snow. This problem may be in other areas. Assess the snow stability on all steep slopes, especially east facing.
Bottom Line:
In the North Valley and upper elevations the avalanche danger is estimated to be MODERATE on steeper slopes. Although not widespread, unstable slopes may be found due to several factors:
1 A buried weak layer exists 1 to 2 feet deep on old crusts on some east facing slopes and has been producing slab avalanches
2 Recently formed wind slabs due to yesterday's wind.
3 Loose sluffing will occur on very steep slopes, these sluffs are becoming fairly large.
In the Central and South Valley and areas receiving only small amounts of snow this past week the avalanche danger is generally LOW.
Weekend Outlook:- A fast moving storm is forecast to enter our region this afternoon and deposit 5 to 7 inches of snow in the mountains by tomorrow morning, accompanied by strong winds. This storm will increase the avalanche danger if it pans out.
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Primary Avalanche Concern:
Another human triggered avalanche occurred along Titus Ridge yesterday, much larger than previous ones this week. See the photos at the bottom of the advisory. No one was caught as the party was cautious, but the size was large- more than 100 feet across and 18” deep. The avalanche was triggered from a short distance above and ran on a northeast facing slope, mostly mid thirty degrees and steeper. The upper portion broke back onto lower slope angles towards the person who was getting ready to dig a pit. It broke and ran due to the weak faceted layer sitting on a buried crust we have been concerned about for a week now.
This is a big heads up. The problem so far has only been observed in the Galena Summit area above 9,000ft. But it is persistent and the slides are getting bigger due to more new snow. This means it will be important to look for buried weak layers and treat similar slopes as being avalanche prone until examined. Dig some pits. To be stable, the slope should have fully consolidated snow and no easy shears in the top 1 to 2 feet of snow. Stay alert, don’t get surprised.
Secondary Avalanche Concern:
Where recent snow has accumulated with more than 6 or 8 inches, very steep north facing slopes continue to produce loose sluffs, Some of these are getting fairly large. In the northern sector snow totals are now 1 to more than 2 feet of new snow since mid March.
We probably won't get enough sun this morning to produce loose wet sluffs of the new snow on steep solar aspects.
Additional concerns-Windslabs: We have not received any recent reports or made our own observations of sensitive windslabs. However yesterday’s strong northwest wind and blowing snow make windslabs a factor to watch for today in exposed areas.
Wind drifting and loading may also play a factor in increasing the avalanche danger on east facing slopes that have the buried weak layer problem.
Current Conditions:
Spring is happening in the Central and South Valley in spite of unusually cold temperatures. With a good shot of sun, solar aspects produce real spring and corn snow conditions. Powder still lingers on the shaded north.
In the North Valley and further back in the mountains, mid-winter conditions are prevalent. Excellent foot deep powder exists on north faces. South facing has gotten too much snow to be pure spring conditions, you’ll find sticky snow or layered crusts depending on location and timing. Yesterday’s northwest wind did some damage to any exposed slopes.
This morning’s temperatures are very cold for late March. Zero degrees at 10,000ft, 9 degrees on Baldy and 4 degrees in Ketchum. Yesterday’s northwest wind gusted over 30mph at upper elevations. They have died down this morning but are expected to increase throughout the day.
Mountain Weather Forecast:
Early morning clear skies are already beginning to cloud over and are forecast to be mostly cloudy by afternoon with a fast moving, hard hitting winter storm by tonight. The jet stream will be directly overhead bringing very cold temperatures, strong southerly winds and blowing snow with very poor visibility. One to three inches of snow is expected on the valley floor and 5 to 7 inches of snow at upper elevations. Temperatures today are forecast to reach highs in teh low twenties.
The weekend forecast is for cold and unsettled conditions.
Photos:
1. Triggered Slide Titus Ridge
2. Titus Slide Near Trigger Point
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
-1 |
7 |
4 |
| 6am Temperature |
-1 |
9 |
4 |
| 24 hr Maximum |
15 |
21 |
35 |
| Winds |
| Note: Soldier Mtn avg 21NWG69 |
| Current Winds |
4W |
1-5NW |
- |
| 24 hr Average |
9NW |
10NW |
- |
| Maximum Gust |
32NW |
29NW |
- |
| Snow - Storm Interval # 18 |
| Total Depth |
77" |
73" |
36" |
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