THIS AVALANCHE ADVISORY EXPIRED ON December 23, 2017 @ 6:49 am
Avalanche Advisory published on December 22, 2017 @ 6:49 am
Issued by Melissa Hendrickson - Idaho Panhandle Avalanche Center

St. Regis Basin/Silver Valley

bottom line

This weeks storms dumped 25 to 30 inches of snow, now burying the surface hoar and faceting that had developed on top of the Thanksgiving crust.  This is providing an unstable layer underneath all this new white that is a potential trigger point for avalanches on slopes >30.  This persistent weak layer will continue to be sensitive to triggers. Careful route finidng and conservative decision-making are essential for backcountry travel today.

How to read the advisory

St. Regis Basin/Silver Valley

How to read the advisory

This weeks storms dumped 25 to 30 inches of snow, now burying the surface hoar and faceting that had developed on top of the Thanksgiving crust.  This is providing an unstable layer underneath all this new white that is a potential trigger point for avalanches on slopes >30.  This persistent weak layer will continue to be sensitive to triggers. Careful route finidng and conservative decision-making are essential for backcountry travel today.

3. Considerable

?

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

3. Considerable

?

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

3. Considerable

?

Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Slabs of new snow ranging up to 30 inches thick recently formed over a mix of surface hoar, facets, and crusts. These slabs are found at all aspects and elevations, but are thicker and more widespread at mid and upper elevations. Observations of collapsing and cracking are evidence that these slabs remain active to human triggers

Avalanche Problem 2: Wind Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Shifting winds with gusts in the transport speed range have created localized pockets of windslab in the high elevations. Gabe and Melissa didn't see extensive development where they traveled yesterday, but reports from Silver Mountain had windslabs building. Assess your riding terrain and look for pillowy appearance to the snow below ridgelines and in gullies.

recent observations

We traveled to West Willow today, hitting multiple different aspects around the 5800' elevation range.  Pack is consistent on all aspects, with our surface hoar and facets over the Thanksgiving crust.  Extended column tests showed propegation on the top of the surface hoar/facet layer.  The significant loading of earlier in the week has ended, but the persistent weak layer will remain a concern. 

Thanks to Gabe White, IPAC volunteer extrodinaire for helping do observations today.  And a huge thanks to Ian St. John, local pro snowmobiler, for helping bust trail and get further into the backcountry than we were expecting with such a deep new snowpack!

Weather and CURRENT CONDITIONS
Weather observations from the Region
0600 temperature: 19 deg. F.
Max. temperature in the last 24 hours: 20 deg. F.
Average wind direction during the last 24 hours: W
Average wind speed during the last 24 hours: 6 mph
Maximum wind gust in the last 24 hours: 18 mph
New snowfall in the last 24 hours: 2-4 inches
Total snow depth: 37 inches
Two-Day Mountain Weather Forecast Produced in partnership with the Spokane NWS
For 2000 ft. to 4000 ft.
Friday Friday Night Saturday
Weather: Snow Slight chance of snow then partly cloudy Sunny
Temperatures: 16 and falling deg. F. 3 deg. F. 14 deg. F.
Wind Direction: North Northeast North
Wind Speed: 5 to 9 8 5 to 8
Expected snowfall: 1-3 in. 0 in. 0 in.
For 4000 ft. to 6000 ft.
Friday Friday Night Saturday
Weather: Chance of snow Partly cloudy Sunny
Temperatures: 23 and falling deg. F. 6 deg. F. 18 deg. F.
Wind Direction: Northeast Northeast Northeast
Wind Speed: 6 to 9 7 to 9 6
Expected snowfall: <1" in. 0 in. 0 in.
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.