THIS AVALANCHE ADVISORY EXPIRED ON February 4, 2016 @ 7:10 am
Avalanche Advisory published on February 3, 2016 @ 7:10 am
Issued by Dave Bingaman - Payette Avalanche Center
bottom line

The Avalanche Danger is Moderate today. Exercise caution in the upper elevations on wind loaded terrain and on protected slopes where surface hoar and other weak layers have been preserved below the new snow,  In these areas human triggered avalanches are more likely on windloaded slopes over 30 degrees,  Moderate Danger means heightened avalanche danger on specific terrain features, careful snowpack and terrain evaluation is essential.

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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Wind slabs in the upper elevations remain our primary concern today.  Expect to find wind slabs of varying thickness and hardness on north, northeast, northwest and cross loaded west and east 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 and middle elevations and range in sensitivity from touchy to unreactive. Shallow wind slabs are more likely right now but you may also find some deeper ones still lingering under a layer of new snow. 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 new layer of buried surface hoar that was formed early last week, or even worse could step down to buried surface hoar that formed in early January. With  South winds increasing today and through tomorrow expect to see some substantial wind transport and wind loading of the light density snow that fell over the weekend in the upper elevations.

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 that continued through Monday of last week.  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 probably 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.

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 Thursday as the storm entered our area. This upper layer is 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.  If you are skiing or riding on steep Northerly or protected slopes, you are literally rolling the dice on whether you are going to step on a land mine unless you take the time to evaluate the upper snowpack before you commit.  Both of these layers are easily identifiable as a gray line or layer in the snow when you dig through them.

Avalanche Problem 3: Loose Dry
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Steep upper elevation slopes especially on Southerly or SE aspects have been shedding some of the loose snow on the surface. We saw several recent sluff piles that were big enough to push you around if you were skiing in them.  The sun has begun to affect the solar aspects too so the sluff problem may become more of a roller ball/wet sluff problem as the snow heats up through the day.  We also found just a little, thin crust on the due south slopes.

advisory discussion

Don't forget about upcoming PAC events:

Feb 3 Forecaster Roundtable- 

Join the Payette Avalanche Center Forecasters each Wednesday in February to discuss a different avalanche topic ( weather and snowpack, terrain and route finding, Human Factors, and Rescue Fundamentals).

When/Where: February 3rd, 10th, 17th, 24th 6:30-8:00 PM @ McCall Ranger Station

 

Feb. 13: Friends of the Payette Avalanche Center Fund Raiser-

 Little Ski Hill. 6-9 PM, Silent Auction, Door Prizes, Timed Beacon Races,  Night Skiing, Locally made beverages and BBQ, KIDS FREE, adults $10 at the door.  This may be our best fundraiser/party yet.

 

 

recent observations

We toured into the Pot Lake drainage in Lick Creek Canyon yesterday to look for the buried surface hoar layer that we have been tracking in other areas.  We did not find it in our pit on a NNW aspect but found several layers of Grauple resting on a layer of rounded Near Surface Facets which produced dirty but low scoring shears in our Compression Tests( CT 8 Q3/PC ) but failed to propagate in Extended Column Tests partially from the  amount of unconsolidated snow above it.  The layer was found near 50 cm and did not fail on ski cuts on similar slopes.  Soft, shallow wind slabs were found on N/NE terrain and produced minimal cracking on ski cuts. We could not find the preserved Surface Hoar layer deeper in our pit similar to the one responsible for the Twin Lakes fatality. The depth of the snowpack on the windloaded NNW slope we chose for our pit yesterday was approaching 13 feet and terrain features are beginning to disapear across a lot of our terrain. 

weather

Expect cold and windy condtions today with a high of 24 and wind chills in the single digits.  Look for increasing South winds in the afternoon with gusts in the mid 20's in the mountains as another storm pushes into the West Central later in the day.  Overnight, 2-4 inches of snow is forecasted with SW winds in the teens.  Tomorrow through Saturday we will have below normal temps and a chance of light accumulations each day with a significant warmup on tap for next week.

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Wednesday Wednesday Night Thursday
Weather: Mostly cloudy, with a high near 24. Calm wind becoming south around 6 mph in the afternoon. Snow likely, mainly after 11pm. Cloudy, with a low around 20. South southeast wind around 5 mph becoming calm after midnight. Chance of precipitation is 70%. New snow accumulation of 1 to 3 inches possible. Snow likely before 11am, then a chance of snow showers after 11am. Cloudy, with a high near 29. Calm wind becoming southwest around 6 mph in the afternoon. Chance of precipitation is 60%. New snow accumulation of less than one inch possible.
Temperatures: 24 deg. F. 20 deg. F. 29 deg. F.
Wind direction: Calm becoming South S/SE SW
Wind speed: 6 5 becoming calm 6
Expected snowfall: 0 in. 1-3 in. Trace in.
Granite Mountain at 7700 feet.
  Wednesday Wednesday Night Thursday
Weather: A 20 percent chance of snow after 11am. Mostly cloudy, with a high near 24. Wind chill values between zero and 10. South wind 5 to 14 mph, with gusts as high as 24 mph. Snow. Low around 17. South southwest wind 13 to 16 mph. Chance of precipitation is 100%. New snow accumulation of 2 to 4 inches possible. Snow before 11am, then a chance of snow showers after 11am. High near 28. West southwest wind around 11 mph, with gusts as high as 21 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 2 inches possible.
Temperatures: 24 deg. F. 17 deg. F. 28 deg. F.
Wind direction: S S/SW W/SW
Wind speed: 5-14, gusting to 24 13-16 11 with gusts to 21
Expected snowfall: Trace in. 2-4 in. 1-2 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.