THIS AVALANCHE ADVISORY EXPIRED ON February 23, 2018 @ 6:54 pm
Avalanche Advisory published on February 22, 2018 @ 6:54 pm
Issued by Eric Morgan - Idaho Panhandle Avalanche Center

Selkirks/Cabinets
St. Regis Basin/Silver Valley

bottom line

Snowpack is consolidating with light powder on the surface where it is not wind affected.  Assess upper elevation ridgetops and wind affected areas greater than 35 degrees as it is highly variable.  

How to read the advisory

Selkirks/Cabinets
St. Regis Basin/Silver Valley

How to read the advisory

Snowpack is consolidating with light powder on the surface where it is not wind affected.  Assess upper elevation ridgetops and wind affected areas greater than 35 degrees as it is highly variable.  

2. Moderate

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

1. Low

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Near Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

1. Low

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Below Treeline
Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.
    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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  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Recent winds from the cold front passage came from the N, NE, and SW with most all extreme ridgetop aspects getting wind.  Watch for exposed areas out of the trees on steep exposed slopes greater than 35 degrees.  

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

The recent storm snow has been there for most of the week, with cold temperatures it is still light and fluffy.  No propogation was observed or seen on our extended column tests.  It is very low density and non cohesive.  Watch for the new snow coming in and assess the density of that new snowfall on the current light snow surface.  

advisory discussion
Friday through Sunday night:  Three shortwaves will drop into the
Northwestern US between Friday and Sunday night. The first wave
will usher a quick moving frontal band of snow through the region
from west to east Friday afternoon. Timing is bit slower than
previous runs however snow amounts still look light as the system
weakens while reaching the Idaho Panhandle. A second wave will
bring the potential for heavier snows Friday night into Saturday.
This will be a stronger shortwave with a much more pronounced
upper-level cold pool. Consequently, the atmosphere will become
increasingly unstable supporting bands of heavier snow showers.
Moderate midlevel flow Friday night and Saturday will highly favor
the Cascade Crest and Idaho Panhandle for the heaviest snow
amounts with a great deal of shadowing in the lee of the Cascades.
However, given the steep lapse rates and strong westerly flow
across the barrier, we anticipate a good deal of slop over snow
into the valleys of western Chelan and Okanogan Counties,
expanding as far east as Wenatchee and the Waterville Plateau at
times. Following a break Saturday night, a third and broader
shortwave sags in from the Sunday. This will be the warmest and
windiest system of the weekend with some uncertainty still
existing how strong the winds may become. Westerly flow
accompanying this system will also lead to the heaviest snow
amounts on the Cascade Crest and again Idaho Panhandle with
similar amounts to Friday/Saturday.

* Snow: Preliminary snowfall amounts for Friday into Saturday range
  from under half an inch in the southwestern Basin and Wenatchee
  Area toward 1-3 inches across northern WA and far north
  Panhandle. Amounts increase into the 3-5 inch range along the
  I-90 corridor from Cd`A to the Montana Border, Palouse (mainly
  east of St John to Mayview), Camas Prairie, and Blue Mtns. The
  heaviest amounts are expected in the Central Panhandle Mtns of
  southern Shoshone County impacting the St Joe R
recent observations

Up in Roman Nose Thursday we found surprisingly light epic powder conditions on most aspects mid and upper elevations.  The pack was very consolidated and stable where we were riding.  I was unwilling to be exposed to extreme steeper terrain with high consequences due to the variability of winds on extreme terrain.  Foot penetration was about 30 cm which made the snowmobiling quite forgiving and provided good conditions to work on skill while still being soft deep.  

Much the same conditions are being found in the Silver Valley area.  Pit tests show that the storm slabs are bonding well and there are lingering windslabs that are working on stabilizing.

Weather and CURRENT CONDITIONS
weather summary
Today......Snow, mainly after 4pm. High near 15. Wind chill values as low as -10. Southwest wind 9 to 14 mph. Chance of precipitation is 80%. New snow accumulation of less than one inch possible.
Tonight
Snow. Low around 14. Wind chill values as low as zero. Southwest wind 9 to 13 mph. Chance of precipitation is 100%. New snow accumulation of 2 to 4 inches possible.
Saturday
Snow likely, mainly before 10am. Mostly cloudy, with a high near 24. West wind 6 to 9 mph. Chance of precipitation is 70%. New snow accumulation of 1 to 2 inches possible.
Saturday Night
Snow, mainly after 4am. The snow could be heavy at times. Low around 15. Southwest wind 9 to 13 mph. Chance of precipitation is 80%. New snow accumulation of 1 to 3 inches possible.
Sunday
Snow, mainly before 4pm. The snow could be heavy at times. High near 25. Breezy. Chance of precipitation is 100%. New snow accumulation of 3 to 5 inches possible. 
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.