THIS AVALANCHE ADVISORY EXPIRED ON December 15, 2018 @ 7:06 am
Avalanche Advisory published on December 14, 2018 @ 7:06 am
Issued by Melissa Hendrickson - Idaho Panhandle Avalanche Center

St. Regis Basin/Silver Valley

bottom line

Last week's cold, dry weather left us with a blanket of well-developed surface hoar that was subsequently buried by 10 to 15 inches of snow from the Monday through Thursday storms. Especially at higher elevations, this surface hoar was buried intact forming a weak layer under our new storm slab.  Strong winds accompanied the new precipitation that came in yesterday and will continue to move snow around creating wind slabs on the ridges and mountain tops.  

How to read the advisory

St. Regis Basin/Silver Valley

How to read the advisory

Last week's cold, dry weather left us with a blanket of well-developed surface hoar that was subsequently buried by 10 to 15 inches of snow from the Monday through Thursday storms. Especially at higher elevations, this surface hoar was buried intact forming a weak layer under our new storm slab.  Strong winds accompanied the new precipitation that came in yesterday and will continue to move snow around creating wind slabs on the ridges and mountain tops.  

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.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Wind Slab
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Strong winds were creating wind slabs on the ridges and mountain tops yesterday.  Winds were primarily from the south-southwest, depositing snow on the north to northeast aspects, but the local weather observation stations recorded periods of swirling winds.  Keep your eyes peeled for wind slabs which look like smooth, rounded pillows of snow that are chalky white in color.  They may sound hollow as you are skiing over them on more mellow terrain.  

Avalanche Problem 2: Persistent Slab
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Surface faceting during last week's cold spell was widespread around the region.  These delicate crystals got buried intact at the higher elevations where the storm came in colder than it did at the mid and lower elevations.  Stability tests yesterday showed this layer to be easily triggered.  Natural avalanches were evident on multiple aspects that had slid on this layer.  It is important to dig down at your location to assess if this layer is present before you commit to larger slopes.  As the season progress and we build up more snow, we will have to keep an eye on this layers behavior. 

recent observations

We travelled to West Willow yesterday and found around 30cm of new snow from the storms this week, which brings the pack total to around 90cm at 6000ft.  There were multiple natural avalanches that had slid on Wednesday, including one which the crown spanned much of one of the bowls above Lone Lake (picture).  All aspects had buried surface hoar present as well as two ice crust layers a little further down in the pack that had rounding facets under them. These were also reactive in pit tests, but not as reactive as the surface hoar layer.  In areas that don't have the buried surface hoar, these might be more of a problem.  As always, check your location to see what layers are in the snowpack.  At the lower and mid elevations, stumps and trees are still a major problem with the low snow amounts and are working well to anchor the pack the lower you get!

Submit observations at the button to the left or feel free to send them to my email, mrhendrickson@fs.fed.us

Weather and CURRENT CONDITIONS
Two-Day Mountain Weather Forecast Produced in partnership with the Spokane NWS
For 2000 ft. to 4000 ft.
Friday Friday Night Saturday
Weather: Partly Sunny Rain Likely then Rain/Snow Likely Slight chance of Snow then partly sunny
Temperatures: 40 deg. F. 30 deg. F. 34 deg. F.
Wind Direction: E becoming S SW SW
Wind Speed: 9-11 14-16, G32 5-9, G21
Expected snowfall: 0 in. <0.5 in. 0 in.
For 4000 ft. to 6000 ft.
Friday Friday Night Saturday
Weather: Partly Sunny and Windy Snow and Windy Chance Snow and Windy then slight chance snow and breezy
Temperatures: 32 deg. F. 24 deg. F. 26 deg. F.
Wind Direction: S SW SW
Wind Speed: 24-30, G41 31-34, G46 23-28, G37
Expected snowfall: 0 in. 2-4 in. <.5 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.

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