THIS AVALANCHE ADVISORY EXPIRED ON December 30, 2017 @ 6:49 am
Avalanche Advisory published on December 29, 2017 @ 6:49 am
Issued by Melissa Hendrickson - Idaho Panhandle Avalanche Center

St. Regis Basin/Silver Valley

bottom line

Heavy snowfall has been and is currently falling and will continue throught the advisory period with snowfall rates up to an inch an hour.  Avalanche activity is expected to increase during the advisory period.  Storm slabs can be triggered easily by skiers.  Windloading has occured on the SE - N aspects, with extensive windslabs and cornices observed at the higher elevations. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential in the backcountry today. 

How to read the advisory

St. Regis Basin/Silver Valley

How to read the advisory

Heavy snowfall has been and is currently falling and will continue throught the advisory period with snowfall rates up to an inch an hour.  Avalanche activity is expected to increase during the advisory period.  Storm slabs can be triggered easily by skiers.  Windloading has occured on the SE - N aspects, with extensive windslabs and cornices observed at the higher elevations. Careful snowpack evaluation, cautious route-finding and conservative decision making are essential in the backcountry today. 

4. High

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Above Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

4. High

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Near Treeline
Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

3. Considerable

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Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.
Avalanche Problem 1: Storm Slab
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A heavy, dense storm slab, fueled by strong winds and heavy snowfall has formed and will continue to form over the next 24 hours. 

Avalanche Problem 2: Wind Slab
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Shifting winds during the storm has created wind loading on N - SE aspects at mid elevations and on all aspects at higher elevations. 

Avalanche Problem 3: Persistent Slab
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There are still facets and surface hoar lurking in the snowpack on top of that Thanksgiving crust. Stability tests showed that they are gaining strength, however this new, rapid snow loading could put them to the test. If triggered, they will create very large avalanches

recent observations

Melissa and Panhandle Backcountry host Larry Banks travelled to Glidden Ridge on the Idaho-Montana border yesterday. Pit data had storm slab failures on 1 tap on all aspects, with the storm slab only getting thicker during the advisory period.  Scouring, windslab, and cornice formation were observed, with the majority of the windslabs in the SE - N aspects.  They were able to find the persistent weak layer of facets and surface hoar on the Thanksgiving crust on all aspects.  

Silver Mountain Ski patrol reported that ski cutting was producing D1 to D2 slides from the storm slabs and windloading. 

Weather and CURRENT CONDITIONS
Weather observations from the Region
0600 temperature: 26 deg. F.
Max. temperature in the last 24 hours: 27 deg. F.
Average wind direction during the last 24 hours: SW
Average wind speed during the last 24 hours: 7 mph
Maximum wind gust in the last 24 hours: 20 mph
New snowfall in the last 24 hours: 10 - 14 inches
Total snow depth: 46 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 then Rain/Snow Rain/Snow and Breezy Snow Likely
Temperatures: 32 and dropping deg. F. 27 deg. F. 29 deg. F.
Wind Direction: East East to southwest Southwest
Wind Speed: 6 - 11 10 - 18 7 -15, gusts 25
Expected snowfall: 3 - 5 in. <0.5in in. 1 to 2 in.
For 4000 ft. to 6000 ft.
Friday Friday Night Saturday
Weather: Heavy Snow Heavy Snow and Windy Snow and Breezy
Temperatures: 29 and falling deg. F. 21 deg. F. 25 deg. F.
Wind Direction: West Southwest West
Wind Speed: 6-10 15-25, gusts 33 14-24, gusts 39
Expected snowfall: 8 to 12 in. 9-13 in. 2 - 4 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.