THIS AVALANCHE ADVISORY EXPIRED ON February 10, 2016 @ 6:27 am
Avalanche Advisory published on February 9, 2016 @ 6:27 am
Issued by George Halcom - Payette Avalanche Center
bottom line

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 hazard of heat triggered avalanches on all solar aspects will increase during the day with rising, inverted temperatures. 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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Expect to find wind slabs of varying thickness and hardness on east, north, northeast, northwest and cross loaded west aspects. Recent, North winds have sculpted, and created fresh wind slabs. 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. The wind 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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Inverted temperatures, and intense solar radiation are the trend.  Wet/Loose slides, and roller ball activity have been on the increase, and temperatures in the mountains are hovering near 50 degrees.  Be wary of sunny aspects as they warm, and become less stable in the afternoon. Remember rapid warming is a red flag avalanche warning, pay attention to changing snow conditions through the day, and move to cooler aspects.

advisory discussion

That's right folks, it's almost time for our annual fundraiser...This Saturday at the Little Ski Hill from 6-9 ish.  Some of the goods: 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 beacon races with great prizes.  Family Friendly environment 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

 The entire advisory area is seeing warming of the snow surface due to the inversion, and sunny skies. Roller balls, point releases, and tree bombs (all signs of warming snow) will continue through this week. Be on the look out for these Red Flag indications of the snow surface warming as you are out traveling today. Objectives are best accomplished early in the day to avoid travailing in terrain where wet snow avalanches will be a concern. 

weather

 

An inversion will persist keeping the valley slightly cooler than the mountains through the week. Temperatures and winds will be stronger in the upper elevations with daytime highs around 46 degrees, and winds out of the Southwest 9-13 MPH. The next chance of precipitation is Saturday, but the large ridge currently over us could push any available moisture to the north of us, and is forecasted to set in for next week as well, looking like a re-peat...dont forget your sunscreen.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Tuesday Tuesday Night Wednesday
Weather: Sunny, with a high near 36. Calm wind. Mostly clear, with a low around 21. Calm wind. Patchy fog. Otherwise, mostly sunny, with a high near 37. Calm wind.
Temperatures: High 36 deg. F. Low 21 deg. F. High 37 deg. F.
Wind direction: South
Wind speed: Calm Calm Calm
Expected snowfall: 0 in. 0 in. 0 in.
Granite Mountain at 7700 feet.
  Tuesday Tuesday Night Wednesday
Weather: Sunny, with a high near 46. Southwest wind 9 to 13 mph. Mostly clear, with a low around 34. Breezy, with a west southwest wind 16 to 20 mph. Patchy fog. Otherwise, mostly sunny, with a high near 43. Breezy, with a west wind 17 to 20 mph.
Temperatures: High 46 deg. F. Low 34 deg. F. High 43 deg. F.
Wind direction: Southwest West, Southwest West
Wind speed: 9-13 MPH 16-20 MPH 17-20 MPH
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.