Avalanche Advisory published on February 5, 2016 @ 5:29 am
This advisory is valid for 24 hours
Issued by - George Halcom
bottom line

The avalanche danger is MODERATE today. Evaluate slopes steeper than 30 degrees. Human triggered avalanches are still possible, especially on windloaded slopes over 30 degrees, and on thin areas of snow with buried surface hoar.  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
View North American Danger Scale


Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Natural avalanches unlikely; human-triggered avalanches possible. Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    likely
    unlikely
  • Size ?
    large
    small
  • Trend ?
    Increasing Danger

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
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    likely
    unlikely
  • Size ?
    large
    small
  • Trend ?
    Decreasing Danger

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).

 

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

 

Our buried surface hoar from our cool, dry spell,  just before MLK day, that has been responsible for many close calls and one tragic accident, is still showing up in our pits. Yesterday, out East of Jug and Boulder Mountain on a North aspect around 7700 FT, we found the same layer buried around 106 CM/3.5 feet, and has some quite hard and strong snow resting above it. This layer is going to be hanging around for a while, and was not as well preserved here as it was the day before out near Lyods Lake, and not as reactive in our stability tests. We are also seeing moderate results about 50CM down from the surface where facets have formed from cold snow surface temperatures producing a clean shear, CTMQ2.

CURRENT CONDITIONS  Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: deg. F.
Max. temperature in the last 24 hours: deg. F.
Average wind direction during the last 24 hours:
Average wind speed during the last 24 hours: mph
Maximum wind gust in the last 24 hours: mph
New snowfall in the last 24 hours: inches
Total snow depth: inches
weather

In the last 24 hours we have picked up around 6 inches of snow...expect slightly warmer temperatures today, and mostly cloudy skies with a high around 33 around 7700 feet, moderate Southwest winds, and little to no accumulation expexted. Another brief cold front will push in this afternoon bringing a few more inches of snow tonight, then we really begin a warming trend , especially up high where we are forecasted to have an inversion, and sunny skies setting in Sunday with temperatures next week somewhere between 40 and 50 degrees in the upper elevations.

Two-Day Mountain Weather Forecast  Produced in partnership with the NOAA-NWS
McCall Airport at 5021 feet.
  Today Tonight Saturday
Weather: Areas of fog before 11am. Otherwise, mostly cloudy, with a high near 32. Calm wind becoming south 5 to 7 mph in the afternoon. Snow, mainly after 11pm. Low around 25. South wind 7 to 9 mph. Chance of precipitation is 80%. New snow accumulation of around an inch possible. A 30 percent chance of snow showers, mainly before 11am. Mostly cloudy, with a high near 33. Southwest wind 3 to 6 mph. New snow accumulation of less than a half inch possible.
Temperatures: High 32 deg. F. Low 25 deg. F. High 33 deg. F.
Wind direction: South South Southwest
Wind speed: 5-7 7-9 3-6
Expected snowfall: 0 in. 1 in. less than one half in.
Granite Mountain at 7700 feet.
  Today Tonight Saturday
Weather: Snow, mainly before noon, then snow showers likely after noon. High near 27. Isolated snow showers before 11am. Mostly cloudy, with a high near 33. Southwest wind 8 to 18 mph. Chance of precipitation is 20%. Snow, mainly after 11pm. Low around 20. Breezy, with a southwest wind 20 to 28 mph, with gusts as high as 38 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible. A 40 percent chance of snow showers. Mostly cloudy, with a high near 31. West wind 9 to 16 mph. New snow accumulation of less than one inch possible.
Temperatures: High 33 deg. F. Low 20 deg. F. High 31 deg. F.
Wind direction: Southwest Southwest West
Wind speed: 8-18 20-28 gusts 38MPH 9-16
Expected snowfall: 0 in. 1-3 in. less than one 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.

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