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This is Chris Lundy of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Wednesday, March 10, 2010 at 7:30 am.
Blaine County Search and Rescue & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Bottom Line by Region:
 North Wood River Valley
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The avalanche danger is estimated to MODERATE. Areas of CONSIDERABLE danger exist on steep, shaded slopes at mid to upper elevations. Dangerous avalanche conditions continue to present where surface hoar and faceted snow are buried 12-18 inches deep. This layering is most widespread in the more remote areas of the Smoky Mountains typically accessed by snowmobile. Numerous avalanches have been triggered during the past few days in this region, including several yesterday in Baker Creek. In these regions, shaded slopes steeper than 35 degrees should be avoided. In the North Wood River Valley and Galena Summit area, the distribution of the weak layer is more sporadic and any slope steeper than 35 degrees needs to be carefully evaluated.
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 South & Central Wood River Valley
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The avalanche danger is estimated to CONSIDERABLE on steep, shaded slopes at mid to upper elevations. Dangerous avalanche conditions continue to exist where 12 inches or more of recent snow has accumulated on layers of buried surface hoar and facets. Obvious signs of instability – such as cracking and collapsing – continue to be reported in this region. Shaded slopes steeper than 35 degrees should be avoided where the weak layer is found buried a foot or more deep.
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Salmon Headwaters & Sawtooth Mountains
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In the Salmon Headwaters, the avalanche danger is estimated to CONSIDERABLE on steep, shaded slopes at mid to upper elevations. Dangerous avalanche conditions continue to exist due to layers of surface hoar and facets buried 12-18 inches deep. Obvious signs of instability may be decreasing as time goes by, but triggering a slide on shaded slopes steeper than 35 degrees remains likely and these areas should be avoided.
In the Sawtooths, the avalanche danger is estimated to be MODERATE. This region received much less snow from early March storms, but a layer of surface hoar can still be found about a foot deep on some mid to upper elevation shaded slopes, especially those below treeline. Although the snowpack is generally stable in this region, this layer has surprised several folks over the past few weeks and steep slopes should be evaluated for the presence of this layer.
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Soldier Mountains
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We provide the Bottom Line for the Soldier Mountains on Friday, Saturday, and Sundays at 7:30am. Please continue to read the full advisory as the information may be applicable to this region.
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Primary Avalanche Concern:
We received three observations from the backcountry yesterday, and only one of those three groups didn’t report obviously unstable conditions. A .333 average may be good in baseball, but not when it comes to avalanches. I was in Baker Creek yesterday where the surface hoar layer was widespread, not to mention alive and kicking. We triggered three avalanches at the head of Apollo Creek that released with only small cornice drops (see photo below). These were all 16-20 inches deep and the largest broke out about 300 feet wide. During stability tests, the surface hoar layer produced easy and clean shears (see video, http://www.youtube.com/watch?v=PMuUY-MvWrg ). Skiers in Eagle Creek received lots of cracking and collapsing, including the slope shattering around them on lower angle terrain. Interestingly, the snowpack seemed most unstable once they were down the slope several hundred vertical feet. This can be a dangerous situation as you might think a slope is safe at the top, only to trigger an avalanche mid slope.
The most dangerous conditions exist in the Salmon Headwaters and western Smoky Mountains, including the Baker Creek drainage as well as the Soldier area. Here the surface hoar and facet layers are the most widespread and also the most deeply buried – about 18 inches down. An unstable snowpack is also prevalent in much of the South and Central Valley, especially where the weak layers are buried by a foot or more of recent snow accumulation. Decision making in these regions is relatively easy right now – the best approach is to avoid shaded slopes steeper than 35 degrees.
In the North Wood River Valley and Galena Summit area the weak layers aren’t as widespread, but recreating on steep slopes requires doing your homework. Dig down continually to check for the presence of the weak layers, and look for clean, planar shears during stability tests. If the dog ate your homework or you just choose not to do it, the best approach is to stick to lower angle terrain or run the risk of getting an F. The sporadic distribution of the surface hoar and facets in this region is a double-edged sword; on the one hand it means fewer unstable slopes, but on the other it’s easier to let your guard down and eventually get spanked.
Surface hoar can also be found buried about a foot deep in the Sawtooths, especially on sheltered slopes below treeline. This area received much less snow from the early March storm, but you’ll still want to keep an eye out for the layer to avoid getting surprised like several groups have been over the past month.
Current Conditions:
A few more inches of snow fell during the day yesterday, bringing “storm” totals since Monday night up to 4-6 inches at upper elevations. Mountain temperatures reached the mid 20s to low 30s, and a high of 34 degrees was recorded in Ketchum. During the past 24 hours, ridgeline winds have averaged 5-15 mph from the northwest. Much colder air moved in overnight, and temperatures are currently in the single digits to low teens up high and it’s in the upper teens on the valley floor.
Yesterday’s snowfall freshened up conditions on all aspects. Shady slopes are providing excellent powder, while some southerly aspects have powder on a supportable crust. Beware the slopes that just get a bit of sun, as the newer snow will likely be masking a breakable crust.
Mountain Weather Forecast:
A weak low pressure trough will pass overhead today bringing not much more than partly to mostly cloudy skies. Clearing is expected tonight along with colder temperatures. Today expect high temperatures in the mountains to reach the upper teens to low 20s, while the valley is only forecast to reach 30 degrees. Ridgeline winds should continue to average 5-15 mph from the north.
Photos:
1. Triggered Avalanche in Apollo Creek
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| Reported Conditions |
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| Temperatures |
| Overnight Low |
2 |
10 |
17 |
| 6am Temperature |
2 |
11 |
17 |
| 24 hr Maximum |
23 |
31 |
34 |
| Winds |
| Current Winds |
13 NW |
8 NW |
- |
| 24 hr Average |
8 NW |
7 W |
- |
| Maximum Gust |
20 NW |
17 NW |
- |
| Snow - Storm # 23 |
| New Snow |
1-2" |
1-2" |
Tr" |
| Storm Total |
4" |
4" |
1" |
| Total Depth |
53" |
59" |
22" |
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Announcements:
The annual Warm Springs Winter Elk Closure is in place - this prohibits all travel on south facing slopes in the Warm Springs drainage from Wanderer's Way in Ketchum out to the West Fork.
The Avalanche Rescue Training Park is located in the Festival Meadows, next to Our Lady of the Snows Catholic Church on Sun Valley Road. It is free with easy instructions on the control panel and open all day. All you need is a beacon and probe to practice your skills.
The beacon practice area on Baldy is now located near the trees in the center of Christmas Ridge.
To find out where Sun Valley Heli Skiing plans to operate on any given day, call their status line at 622-2999.
Your observations are invaluable! They help us produce more accurate advisories which in turn helps you. If you get into the backcountry, let us know what you see out there - especially if you see or trigger any avalanches. Call (208)622-0099 or fill out the observer form on our website: http://www.sawtoothavalanche.com/submit_observation.php
For Idaho road closures check http://511.idaho.gov
For a recording of this advisory, call the Avalanche Hotline - (208)622-8027.
This information only applies to the backcountry and does not apply to highway programs or operating ski areas. Changing conditions and local variations may occur.
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