THIS AVALANCHE ADVISORY EXPIRED ON February 8, 2016 @ 6:54 am
Avalanche Advisory published on February 7, 2016 @ 6:54 am
Issued by Dave Bingaman - Payette Avalanche Center
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The Avalanche Danger is MODERATE today. Human triggered avalanches are possible, especially on windloaded slopes and in areas with a layer of buried surface hoar(the layer responsible for last weekend's fatality). The hazard of heat triggered avalanches will increase with rising temperatures over the next few days. Moderate danger means heightened avalanche danger on specific terrain features, careful snowpack and terrain evaluation is essential. Below 6,000 feet generally safe avalanche conditions exist, and the avalanche danger is LOW.

 

How to read the advisory


  • Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
Avalanche Problem 1: Wind Slab
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We have had plenty of light density snow to move around recently with wind transport variable at times but mostly out of the Southwest for the better part of the last week. With that in mind, wind slabs remain our primary concern. Expect to find wind slabs of varying thickness and hardness on east, north, northeast, northwest and cross loaded west aspects. You are most likely to find these slabs at or near the ridge tops or in exposed terrain above 7,000 feet. They are still relatively widespread in the upper elevations and range in sensitivity from touchy to unreactive. Shallow wind slabs are more likely right now within this week's new snow, but you may also find some deeper ones still lingering deeper below the surface.These slabs range in density between soft to hard, which means they may let you get well out onto them before they fail. Also, keep in mind that some of these wind slabs may be resting on a newer layer of buried surface hoar that was formed early last week, or even worse could step down to the buried surface hoar layer that formed in early January. As temperatures increase today and over the next few days some of these windslabs may become unstable as the snowpack warms.  Overhanging cornices may also begin to fail with the heat. if you are on a slope and notice the snow changing, you will want to find cooler slopes or call it a day.

Avalanche Problem 2: Persistent Slab
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We currently have 2 different persistent layers that we are tracking: one is relatively shallow and the other relatively deep. Both layers are made up of either buried surface hoar or near surface facets and represent old surface snow that was subjected to the faceting process during periods of high pressure in between snow cycles.  The deeper layer is the one that resulted in the large and fatal slide near Twin Lakes on Sunday and the substantial natural avalanche cycle that we saw following MLK day.  It is becoming a deep instability problem that is increasingly hard to trigger and not very widespread but is probably unsurvivable if triggered. In hazard evaluation terms it is a LOW probability/HIGH consequence problem.  Its current depth is between 2.5 and 3.5 feet down in the snowpack depending on the windloading on individual slopes.  Unfortunately, this layer is likely to stay where it is for quite some time and Snowmobiles are more likely to trigger it than a skier.  It is also very hard to predict where you will trigger it because of its non-uniform distribution across the larger area and even across individual slopes and small micro features. Shallow wind protected areas well below the ridge tops, areas around rocks or on slopes with rocks sticking out or barely covered that were mostly protected from the winds are our best description for where you might trigger it right now. If you avoid areas with complex or convoluted terrain with lots of varying snow thickness across a slope, you will eliminate a large portion of the risk of triggering this layer, better yet spend your time boondocking through more moderate terrain and leave the steeps alone right now.

The upper layer is also made up of faceted snow or preserved surface hoar that was the snow surface last week before our last round of snowfall.  In addition, we are finding areas with substantial grauple layers that were deposited  a week ago as the last significant storm entered our area. This upper layer is  becoming more stable with time but is more likely to be triggered by skiers or snowmobilers with equal chance due to its proximity to the surface right now. It is also variable where you will find it and what it is comprised of based on the winds, and the type of precipitation that fell on top of it.  Both of these layers are easily identifiable as a gray line or layer in the snow when you dig through them.

A warming trend will add a significant stress to the snowpack as layers begin to melt and add weight and water to the upper snowpack.  Be aware that rapid warming is one of the main red flags and that these will be the warmest temperatures of the winter so far. Persistent weak layers have a tendency to reactivate when the snowpack initially begins to warm up. The possibility of natural and human triggered avalanches will increase with the temperatures over the next few days.

Avalanche Problem 3: Loose Wet
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Watch for a warm up in the snowpack today.  Wet/Loose activity and roller ball activity have been on the increase over the last 2 days and temperatures in the mountains are going to continue to climb.  Be wary of sunny aspects as they warm today and over the next few days. Remember rapid warming is a red flag avalanche warning, pay attention to changing snow conditions as the Death Star turns up the heat.

advisory discussion

That's right folks, it's almost time for our annual fundraiser...next Saturday at the Little Ski Hill from 6-9 ish.  Spoiler alert: Beer from McCall's own SRB, Waverunner rental from Cheap Thrills and skis from Dynafit! Practice up with those beacons and get ready for some timed becon races with great prizes.  Family Friendly with night skiing and plenty of parking available on both sides of the highway. Thanks to all the donors that have supported us in the past and again this year!

recent observations

We toured in the North Country at Tamarack yesterday and found shallow recycled powder and great skiing conditions. Surface instabilities are settling out with the snow.  The upper elevations were sporting a firm and supportable wind board that made ridge cruising pretty easy. We did still find the shallow wind slab on the surface on leeward aspects in the usual spots just below cornices and on unsupported slopes. Crust has begun to form on slopes with even a minor tilt to the South. The lower elevations are beginning to become a little more challenging with a hint of a breakable melt freeze crust and lots of tree bombs shedding below 6000 feet.  

weather

The Inversion is digging in today and temperatures in the upper elevations will reflect that.  Expect highs in the upper 30's today that will feel warmer if the sun is out.  Tomorrow temperatures will climb into the 40's. This is a stationary ridge that will be with us through most of the week.  Valleys will see fog and cooling temperatures while the mountains will continue to warm into the upper 40's and mid 50's by mid week.  A weak trough will push into the area by Friday bring showers but you can expect to see the inversion sticking aroun through next week with most of the available moisture pushing around the north end of the high pressure ridge.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Sunday Sunday Night Monday
Weather: Patchy fog before 11am. Otherwise, mostly sunny, with a high near 33. Calm wind Patchy fog after 11pm. Otherwise, partly cloudy, with a low around 17. Calm wind. Patchy fog before 11am. Otherwise, mostly sunny, with a high near 35. Calm wind.
Temperatures: 33 deg. F. 17 deg. F. 35 deg. F.
Wind direction: Calm Calm Calm
Wind speed: 0 0 0
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Sunday Sunday Night Monday
Weather: Mostly sunny, with a high near 37. West northwest wind around 9 mph. Partly cloudy, with a low around 27. West northwest wind 7 to 9 mph. Sunny, with a high near 41. West wind around 8 mph.
Temperatures: 37 deg. F. 27 deg. F. 41 deg. F.
Wind direction: W/NW W/NW W
Wind speed: 9 7-9 8
Expected snowfall: 0 in. 0 in. 0 in.
Disclaimer

This avalanche advisory is provided through a partnership between the Payette National Forest and the Payette Avalanche Center. This advisory covers the West Central Mountains between Hard Butte on the north and Council Mountain on the south. This advisory applies only to backcountry areas outside established ski area boundaries. This advisory describes general avalanche conditions and local variations always occur. This advisory expires at midnight on the posted day unless otherwise noted. The information in this advisory is provided by the USDA Forest Service who is solely responsible for its content.