THIS AVALANCHE ADVISORY EXPIRED ON February 5, 2016 @ 6:49 am
Avalanche Advisory published on February 4, 2016 @ 6:49 am
Issued by -
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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. 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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With today's winds and new low density snow 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 and middle elevations and range in sensitivity from touchy to unreactive. Shallow wind slabs are more likely right now with today'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 buried surface hoar that formed in early January. With west winds increasing today expect to see wind transport and wind loading of the light density snow that fell overnight and that will fall through the day today.

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 (see picture in OBSERVATION section of forecast).

 

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. With last night and today's new low density snow sluffing will increase on steep slopes over 40 degrees. 

advisory discussion

Don't forget about upcoming PAC events:

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

The PAC forecasters continued there tracking of buried surface hoar yesterday up in the Hazard Lake area. In our first pit we found well preserved and easily identifiable surface hoar layer on a NE aspect at 7350 feet. The buried surface hoar prove to be quite reactive in this particular spot with a CT10 Q1 sudden planner at 85 cm below the snow surface. Continue to look for this layer 80-90 cm below the snow surface when looking for slopes to ski and ride on.Our second pit was at Upper Hazard Lake at an elevation of 7400 feet on a NE aspect. The surface hoar was not present in this pit. However, a graupel layer at 50 cm was present, but was unreactive.

weather

The mountains in the advisory area have picked up 2 inches of low density powder over night. Expect to see another 1-3 inches today with winds blowing 15-25 MPH out west and temps will max out in the mid 20's at 7700 feet. A chance for snow returns Friday night into Saturday before high pressure and warm teps settle into the area for next week. 

Two-Day Mountain Weather Forecast Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Thursday Thursday Night Friday
Weather: Snow likely before 11am, then scattered snow showers after 11am. Cloudy, with a high near 27. Calm wind becoming south southwest 5 to 7 mph in the morning. Chance of precipitation is 70%. New snow accumulation of around an inch possible. A 30 percent chance of snow before 11pm. Areas of fog after 11pm. Otherwise, cloudy, with a low around 17. Light and variable wind. New snow accumulation of less than a half inch possible. Areas of fog before 11am. Otherwise, cloudy, with a high near 31. Calm wind becoming south around 5 mph in the afternoon.
Temperatures: High 27 deg. F. Low 17 deg. F. High 31 deg. F.
Wind direction: south-southwest variable south
Wind speed: 5-7 light calm-55
Expected snowfall: 1 in. less than half inch in. 0 in.
Granite Mountain at 7700 feet.
  Thursday Thursday Night Friday
Weather: Snow, mainly before noon, then snow showers likely after noon. High near 27. Breezy, with a west wind 15 to 21 mph, with gusts as high as 31 mph. Chance of precipitation is 80%. Total daytime snow accumulation of 1 to 3 inches possible. A 40 percent chance of snow, mainly before midnight. Cloudy, with a low around 20. Northwest wind 7 to 14 mph, with gusts as high as 23 mph. New snow accumulation of less than one inch possible. Cloudy, with a high near 32. Southwest wind 7 to 12 mph increasing to 13 to 18 mph in the afternoon. Winds could gust as high as 30 mph.
Temperatures: High 27 deg. F. Low 20 deg. F. High 32 deg. F.
Wind direction: west northwest southwest
Wind speed: 15-21 gusts 31 7-14 gusts 23 7-12 gusts 30
Expected snowfall: 1-3 in. Less than half an inch 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.