THIS AVALANCHE ADVISORY EXPIRED ON February 25, 2018 @ 7:14 am
Avalanche Advisory published on February 24, 2018 @ 7:14 am
Issued by Dave Bingaman - Payette Avalanche Center
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Human triggered avalanches are possible today where isolated wind slabs may be found on upper and middle elevation, wind exposed slopes.  The new snow we received this week may be hiding older wind slabs left from  strong winds earlier this week.  Loose snow avalanches/sluffs are likely on slopes over 35 degrees.  Numerous natural and human caused avalanches occurred in the last 6 days, most of these failed in wind loaded areas where faceted snow was resting on a crust below.

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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Strong winds last week and steady winds in the mid to upper teens over the last few days combined with 20-24 inches of light density (blower!) snow in the last 7 days have created a recipe for wind slab avalanches throughout the West Central Mountains.  Winds have swirled around from the S to the NE during this time creating wind slabs on multiple aspects.  The newest crop of wind slabs is in the 4-14 inch range with older wind slabs as deep as 2.5 feet possible.  Some of these wind slabs from last week are now camouflaged by the addition of new snow above them.  A layer of faceted snow developed in some areas prior to the last 8 days of storms and is resting on the stout crust deposited in late January allowing avalanches in these areas to propagate over larger areas.   These slabs while widespread are not reactive in all areas, your best bet for triggering a shallow or deeper slab is going to be found on steep, upper elevation terrain especially with recently deposited drifts or wind pillows. Watch for visual clues such as sculpted or scalloped snow surfaces, wind spines or drifts or rounded pillow formations all of these features are signs of wind slabs.  Throughout the day today we are going to be adding even more new snow above our existing wind slab problem and these visual clues are going to be harder to pick out.

Winds are currently out of the SW around 10 mph but will be increasing throughout the day and overnight tonight. Pay attention to changing conditions, fluctuations in the temperature over the next few days and the addition of over a foot of new snow in the next 24-36 hours.  The avalanche hazard will rise later in the day today and through the night tonight.

Watch for signs of instability today and through the weekend including:  recent avalanche activity, cracking, collapsing and whumphing in the snowpack.  If you encounter these or signs of denser snow resting on the light snow below, stick to lower angle, less avalanche prone terrain.

Photos are cracking from Thursday in wind drifts on East aspect near 7400 ft, wind sculpted snow on S ridge from Friday close to 8000 feet and NW ridgetop at 8400 ft.

    

Avalanche Problem 2: Loose Dry
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Loose, dry avalanches or sluffs are widespread right now on steep terrain.  Our mountains have received between 17 and 21 inches of new, low density snow over the last 7 days with an additional 3-5 overnight. Widespread natural sluffing and point releases in the light density snow are visible on multiple aspects and on steep terrain at all elevations.  While these small avalanches don't pack a lot of punch, they do have the ability to pile up in terrain traps or steer a skier where they don't want to go.  Use good travel etiquette and keep your eyes on your partners.  Avoid steep, confined and consequential terrain where a small sluff could create larger problems.  Additional storm and wind deposited snow will continue to add to this problem today and tomorrow.

advisory discussion

A big thanks to everyone that came out to the FPAC fundraiser last night!  Thanks for supporting PAC and the Friends!  Thank you also to all of our donors and the McCall Club House/Banyans Restaurant for hosting us!

recent observations

We experienced the full spectrum of snow conditions on our tour of the West face of Granite Mt yesterday.  Ridgetops were sculpted and drifted with occasional patches of leftover January crust exposed in between soft snow and firm drifts.  We also experienced widespread collapsing, cracking and several large whumps where the new firm windslabs were overlying the crust and facet layer around between 12 and 14 inches down.  We were also able to observe wind sculpted and scoured snow on the NW aspect of Granite as well as many small natural point release sluffs in steep terrain on all aspects.   We were able to easily trigger multiple small and very thin but extremely sensitive wind slabs on the 30-35 degree West facing terrain with our skis.  Middle and lower elevation protected slopes proved to have the best skiing and riding with plenty of light fluffy snow and no wind effect.

Given the sensitivity of these small slabs, today would be a good day to stick to lower angle, protected terrain and leave the upper elevation, wind affected terrain alone.  3-5 inches of new snow fell overnight with another 6-10 inches possible through the day today.  Old wind slabs are going to be camoflaged by the new snow which will add to the depth of the problem.  Expect the avalanche hazard to rise today as the snow increases and plan your day and routes accordingly.

CURRENT CONDITIONS Today's Weather Observations From the Granite Weather Station at 7700 ft.:
0600 temperature: 5 deg. F.
Max. temperature in the last 24 hours: 14 deg. F.
Average wind direction during the last 24 hours: WSW
Average wind speed during the last 24 hours: 6 mph
Maximum wind gust in the last 24 hours: 17 mph
New snowfall in the last 24 hours: NA inches
Total snow depth: 72 inches
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.