THIS AVALANCHE ADVISORY EXPIRED ON December 22, 2017 @ 5:13 pm
Avalanche Advisory published on December 21, 2017 @ 5:13 pm
Issued by Kevin Davis - Idaho Panhandle Avalanche Center

Selkirks/Cabinets

bottom line

Steady snow accumulation has been the rule for the past week but the 36 hour dump from Sunday night to Wednesday is what tipped the scales.  We have two feet of unstable snowpack on top of the Thanksgiving crust and the most sensitive layer is within the 36 hour storm snow.  You'll find it about 1.5 feet deep in soft new snow.  It will take a little longer to become stable, especially in steep terrain.

How to read the advisory

Selkirks/Cabinets

How to read the advisory

Steady snow accumulation has been the rule for the past week but the 36 hour dump from Sunday night to Wednesday is what tipped the scales.  We have two feet of unstable snowpack on top of the Thanksgiving crust and the most sensitive layer is within the 36 hour storm snow.  You'll find it about 1.5 feet deep in soft new snow.  It will take a little longer to become stable, especially in steep terrain.

3. Considerable

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Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

2. Moderate

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Near Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

2. Moderate

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Below Treeline
Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
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Fractures came with moderate force in the upper 1.5 feet of storm snow.  The slab density is light in sheltered terrain but will be denser in open exposed terrain where this storm snow weakness will be more sensitive.  We did not reveal buried surface hoar but travel as though it is there, particularly in sheltered areas.

Avalanche Problem 2: Deep Slab
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Due to the cold weather prior to the recent snowfall the layer of snow resting on the Thanksgiving crust is loose and faceted.  This is buried under two feet of new snow and creating a weak base.  There is a possiblity of triggering the weak layer in the new storm snow which then triggers the deeper layer of faceted snow over the crust.  This scenario would be more likely in bigger, open terrain features.

advisory discussion

A big thanks to Idaho Parks and Recreation for donating a POlaris 600RMK to the Avalanche Center.  We took it out in the powder today on our tour and had a blast.  All of us at IPAC wish everyone a very Merry Christmas!  We'll be posting avalanche advisories next week at our regular days of Tuesday and Friday.  Thanks to everyone who has been submitting their observations.  Don't forget to stay tuned to IPAC via Facebook too.  

recent observations

Schweitzer patrol was getting widespread reults with avalanche control work Wednesday morning through ski cutting and use of explosives.  Natural avalanches were also observed.  Slides were occurring in places that had not slid in many years.  To the south, Melissa and Gabe were getting signs of shooting cracks and whoomphing.  Even though Eric and I did not find the tell tale signs yesterday you should assume that slopes are prone to slide until you confirm your suspiscions. 

Weather and CURRENT CONDITIONS
weather summary
Today, a chance of snow before 10am, then scattered snow showers after 10am. Cloudy, with a high near 15. Wind chill values as low as -5. Blustery, with a northeast wind 9 to 18 mph. Chance of precipitation is 40%. Total daytime snow accumulation of less than a half inch possible.  Tonight, mostly cloudy during the early evening, then gradual clearing, with a low around 7. Wind chill values as low as -6. Northeast wind 10 to 15 mph.  Saturday looks sunny, with a high near 12. Wind chill values as low as -5. North wind 5 to 7 mph.  Partly cloudy, with a low around 2. Wind chill values as low as -10. West wind around 7 mph by Saturday evening.  Sunday, a 20 percent chance of snow after 10am. Mostly cloudy, with a high near 14. East wind 6 to 8 mph.  A possibility of snowfall on Christmas eve.
 
Weather observations from the Region
0600 temperature: 16 deg. F.
Max. temperature in the last 24 hours: 18 deg. F.
Average wind direction during the last 24 hours: NW
Average wind speed during the last 24 hours: 20 mph
Maximum wind gust in the last 24 hours: 60 mph
New snowfall in the last 24 hours: 2-4 inches
Total snow depth: 60 inches
Disclaimer

Avalanche conditions change for better or worse continually. Backcountry travelers should be prepared to assess current conditions for themselves, plan their routes of travel accordingly, and never travel alone. Backcountry travelers can reduce their exposure to avalanche hazards by utilizing timbered trails and ridge routes and by avoiding open and exposed terrain with slope angles of 30 degrees or more. Backcountry travelers should carry the necessary avalanche rescue equipment such as a shovel, avalanche probe or probe ski poles, a rescue beacon and a well-equipped first aid kit.  For a recorded version of the Avalanche Advisory call (208)765-7323.