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| 12.17.2009 |
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This is Chris Lundy with the Sawtooth National Forest Avalanche Center with General Snow and Weather Information on Thursday, December 17, 2009.
Starting this Saturday, we will begin issuing the full Avalanche Advisory each morning at 7:30am. This season the advisory will provide separate “Bottom Lines” and danger roses for four different regions: the North Valley, South & Central Valleys, Salmon Headwaters & Sawtooth Mountains, and Soldier Mountains (Fri, Sat, and Sun).
Special Announcement:
While I’m writing this, we just received news of an avalanche accident near McCall, Idaho. Details at this point are limited, but there is one confirmed fatality and another serious injury. More details will be posted on http://www.avalanche.org when they become available.
Mountain Weather:
Finally we’re getting a break from the “stormy” weather that’s lingered since the weekend. Mountain temperatures today and yesterday reached into the mid to upper 20s. Ridgeline winds have been light to moderate from the west to northwest. More of the same is in the forecast for the next few days before the weather becomes unsettled towards the weekend.
Snowpack Discussion:
The snow that fell over the weekend and early this week accumulated on an extremely weak, faceted snowpack but it wasn’t quite enough to cause widespread dangerous conditions. However, regions that received greater amounts of recent snow are starting to show signs of instability.
Janet and I were on Titus Ridge yesterday where we found the recent snowfall had settled out to about 8-10” on top of the facets (see photo below). We did see a couple small natural avalanches on very steep road cuts (see photo), and another was reported today that occurred on Titus Ridge proper. Although our stability tests produced very poor results (see video, http://www.youtube.com/watch?v=WaFZnGBHHFA ), we felt that you would need a very steep slope or one loaded by the wind to trigger an avalanche.
The Sawtooth Valley picked up more snow from the last series of storms, and as a result these areas are a little closer to the tipping point. Yesterday, a backcountry skier in the northern Sawtooths reported just over a foot of newer snow along with signs of instability including collapsing, shooting cracks, and poor stability test scores. In the Salmon Headwaters, a group yesterday found 8-12 inches of settled snow on the facets, observed a natural avalanche and received lots of collapsing and cracking. While walking a ridgeline, they remotely triggered a decent-sized avalanche on a steep, wind loaded slope. While we are lacking weather data and observations from the Soldier Mountains, it sounds like they picked up a good bit of recent snow and this region may also be a concern.
Just because we didn’t receive a ton of snow from the recent storms doesn’t mean that you can’t trigger an avalanche. These reports clearly indicate that there are some slopes out there that are unstable. Very steep slopes greater than about 35 degrees and any slope that has deeper drifts of wind deposited snow should be avoided as these will be the most problematic. We’re starting off the season with a weaker than normal snowpack, and this sort of thing is our specialty. Now is the time to get into the habit of being conservative because this problem will be with us for some time.
A special thanks to the folks that have been sending in reports. Our observations this season are still limited so we’d love to hear what you’re finding. Give us a call at 622-0099 or fill out the observer page on our website.
Photos:
1. Road cut avalanche on Galena Summit
Announcements:
Check http://www.sawtoothavalanche.com/danger.php for a description of avalanche danger ratings.
This forecast only applies to the backcountry and not for highway programs or operating ski areas. Changing conditions and local variations may occur.
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