This is Chris Lundy of the Sawtooth National Forest Avalanche Center with your Backcountry Avalanche Advisory and Weather Forecast for Saturday, March 13, 2010 at 7:30 am.
The Sawtooth Society in partnership with Idaho's SNRA Mountain Goat license plate program & the Friends of the Sawtooth Avalanche Center bring you this advisory.
Bottom Line by Region: North Wood River Valley |
 | The avalanche danger is estimated to be HIGH. New and wind blown snow from today’s storm is adding weight to variety of weak layers within the top 2 feet of the snowpack, and human triggered avalanches are likely on many shaded slopes steeper than 35 degrees. In the North Wood River Valley and Galena Summit area the weak layers haven’t been as widespread, but facets and surface hoar can be found 16-18 inches deep on some shady aspects. Surface hoar buried 18-24 inches deep is widespread in the western Smoky Mountains, including the Baker Creek drainage. Conditions will be especially dangerous on any wind loaded slope. Wind transport will have taken place primarily along upper elevation northerly facing ridgelines, but you may find fresh drifting on other aspects as the wind shifts at the end of today’s storm.
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| South & Central Wood River Valley |
 | The avalanche danger is estimated to be HIGH. New and wind blown snow from today’s storm is adding weight to extremely fragile weak layers buried 12-16 inches deep, and human triggered avalanches are likely on many shaded slopes steeper than 35 degrees. Conditions will be especially dangerous on any wind loaded slope. Wind transport will have taken place primarily along upper elevation northerly facing ridgelines, but you may find fresh drifting on other aspects as the wind shifts at the end of today’s storm.
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| Salmon Headwaters & Sawtooth Mountains |
 | In the Salmon Headwaters, the avalanche danger is estimated to be HIGH. New and wind blown snow from today’s storm is adding weight to a dangerous layer of buried surface hoar 18-24 inches deep, and human triggered avalanches are likely on many shaded slopes steeper than 35 degrees. In the Sawtooths, the avalanche danger is estimated to be CONSIDERABLE. Buried surface hoar exists on some slopes in this region, and steep terrain should be carefully evaluated. Conditions will be especially dangerous on any wind loaded slope. Wind transport will have taken place primarily along upper elevation northerly facing ridgelines, but you may find fresh drifting on other aspects as the wind shifts at the end of today’s storm.
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 Soldier Mountains |
 | The avalanche danger is estimated to be HIGH. New and wind blown snow from today’s storm is adding weight to a dangerous layer of buried surface hoar 18-24 inches deep, and human triggered avalanches are likely on many shaded slopes steeper than 35 degrees. Conditions will be especially dangerous on any wind loaded slope. Wind transport will have taken place primarily along upper elevation northerly facing ridgelines, but you may find fresh drifting on other aspects as the wind shifts at the end of today’s storm.
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Primary Avalanche Concern:
Our region has been plagued with a variety of weak layers that formed during dry spells in mid to late February. Surface hoar and near surface facets remained preserved on many slopes facing east through north through west. These became active with loading in early March, and have been a concern ever since.
In the South and Central Valley, the weak layer consists of a nasty concoction of very sugary facets and surface hoar. While there have been plenty of signs of instability and you wouldn’t have caught me on a slope steeper than 35 degrees, the slab seemed a bit on the shallow side. Well, that’s changed with today’s storm, and there is now 12-16 inches of snow on this fragile weak layer.
The North Wood River Valley has shown better stability over the past week, and although weak layers do exist, they haven’t been as widespread or sensitive. On Galena Summit yesterday, I did find a weak layer of surface hoar or facets on 3 out of 4 pits, but I didn’t get the scary results during snowpit tests that I’ve seen in other parts of our region. Stability evaluation in this region is going to be tricky, I think you could get away with playing on many steep slopes but there are definitely places where you could trigger a slide. You’ll have to carefully evaluate each slope you plan to ski or ride by digging down and looking for clean and/or easy shears within the top 2 feet of the snowpack.
Possibly the most dangerous portion of our region is the western Smoky Mountains, including the Salmon Headwaters, Baker Creek drainage, and Soldier region – areas typically accessed by snowmobile. In these areas a relatively widespread layer of surface hoar is buried 18-24 inches deep. We have seen a number of natural and triggered slides in these regions over the past week, and Blase and I observed significant signs of instability in the Soldiers as recently as last Thursday. Today’s additional load will make this layer more sensitive and also increase the potential size of any avalanche. The best tactic in these regions is to avoid north-tending slopes steeper than 35 degrees.
The Sawtooths also have surface hoar buried about a foot deep, and although it missed out on the early March loading event, it has still remained a concern. Although its distribution is sporadic, it is most prevalent on sheltered slopes below treeline but may be found in the alpine. This storm may re-awaken it so exercise caution on slopes where it may exist.
Secondary Avalanche Concern:
Strong south to southeast winds before and during the storm will have transported additional snow onto northerly facing leeward slopes. These winds seem to be more intense in the northern portion of our region, including Galena Summit and the Sawtooths. Avoid drifted and pillowed slopes as the additional weight of the wind blown snow could be overloading buried weak layers. Ridgeline winds will change direction and become gusty at the tail end of today’s storm, so watch for new wind loading on other aspects as the day goes on.
Current Conditions:
Snowfall began last night around midnight, and as of 7am most of our region has received about 6 inches of new snow. South to southeasterly winds increased dramatically yesterday in the northern portion of our region, and for 12 hours the winds on Titus Ridge exceeded 30 mph with gusts over 40 mph. They were less dramatic on Baldy and in the Soldier Mountains, but still averaged in the 15-30 mph range. This morning they have eased a bit and have begun to shift to the west as a cold front approaches.
Spring time powder conditions will prevail today, and colder temps and cloud cover should keep the snow quality good through the day. Powder on supportable crusts should be common on many solar aspects, and will be a good approach to avoiding the instabilities found on many northerly aspects.
Mountain Weather Forecast:
A deep low pressure trough is moving through our region, and a cold front should arrive this morning. Although the front will likely spell the end of the bulk of the snowfall, we could still see another 2-4 inches accumulate by the end of the day. Tonight will likely bring some clearing with high pressure building for Sunday. It will be a difficult call to predict how much temperatures will warm today after the passage of the cold front, but they will likely reach the low to mid 20s at upper elevations and the mid to upper 30s down in the valley. Ridgeline winds should average 15-25 mph, continuing a shift towards a more northerly direction and becoming gusty even in the valley.
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| Reported Conditions | |  | |  | |  |
| Temperatures |
| Overnight Low | 18 | 20 | 28 |
| 6am Temperature | 20 | 21 | 28 |
| 24 hr Maximum | 24 | 30 | 40 |
| Winds |
| Current Winds | 16 S | 13 SE | - |
| 24 hr Average | 26 S | 11 SE | - |
| Maximum Gust | 48 S | 24 SE | - |
| Snow - Storm # 24 |
| New Snow | 6" | 6" | 6" |
| Total Depth | 56" | 62" | 26" |
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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 park will close for the season on March 10.
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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