THIS AVALANCHE ADVISORY EXPIRED ON January 4, 2020 @ 5:54 am
Avalanche Advisory published on January 3, 2020 @ 5:54 am
Issued by Melissa Hendrickson - Idaho Panhandle Avalanche Center

St. Regis Basin/Silver Valley

bottom line

Complicated weather makes for complicated snowpack layers. Simplified, there are lots of windslabs and crossloading out there, with more forming over the weekend.  We have a multitude of buried persistent weak layers, the most reactive being a buried surface hoar layer from earlier this week. Avoid both these problems by riding conservative terrain.

How to read the advisory

St. Regis Basin/Silver Valley

How to read the advisory

Complicated weather makes for complicated snowpack layers. Simplified, there are lots of windslabs and crossloading out there, with more forming over the weekend.  We have a multitude of buried persistent weak layers, the most reactive being a buried surface hoar layer from earlier this week. Avoid both these problems by riding conservative 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.

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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While the winds have been predominantly out of the S-SW, we have had swirling winds that have deposited windslabs and crossloading on anywhere it can. With more snow and very high winds forecasted for the weekend, expect this problem to increase in danger. Watch for chalky snow that sounds hollow. If triggered, it is likely that the avalanche will step down to our persistent weak layers to cause a much bigger avalanche. 

Avalanche Problem 2: Persistent Slab
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As soon as our lower pack layers were starting to heal, we had surface hoar layers that formed during the inversion early in the week get  buried with the recent snow. The rain we got on New Years took care of this problem down lower, but at higher elevations this is widespread on all aspects. Check each location you are riding to see if these layers are there. The more you know, the better informed your riding will be.

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Yesterday we traveled to the Grouse Peak area. At the higher elevations, we found crossloading and windslabs on every aspect, not just the north sides. These were up to several feet thick in some locations. Wednesday there was a snowmobile triggered avalanche on a windslab in the Dominion area, no one was injured. These slabs take time to stabilize: don't expect it to happen this weekend. The storms coming in are the perfect recipe for more windslabs and crossloading.

The persistent weak layers got a couple new ones to bundle in with the others. The buried surface hoar is the most reactive and was predominant above 5800' in our location yesterday on all aspects. We were getting full propagation in our extended column tests on all aspects as well. This is enough for us to step back and be conservative. The storm coming in this weekend looks to be a little on the heavy side, so I expect more weight will continue to make this layer likely to be triggered. Red flags include cracking and whumphing, and a sure fire way to know is to dig down to find it with pit tests. One avalanche was triggered on Wednesday on this layer by a snowmobile (everyone OK). 

2020 is off to a tumultuous start with a complicated snowpack! But at least we are getting snow!

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: Chance rain /snow then mostly cloudy Chance rain /snow then rain /snow and breezy Snow and windy then chance snow and breezy
Temperatures: 40 deg. F. 33 deg. F. 37 deg. F.
Wind Direction: S SW SW
Wind Speed: 7-9 9-18 18-25, G36
Expected snowfall: 0 in. <.5 in. <.5 in.
For 4000 ft. to 6000 ft.
Friday Friday Night Saturday
Weather: Windy. Snow likely then mostly cloudy Windy. Chance snow then heavy snow Heavy snow and blowing snow
Temperatures: 35 deg. F. 23 deg. F. 26 deg. F.
Wind Direction: SW S SW
Wind Speed: 28-33, G50 23-33, G55 37-43, G60
Expected snowfall: <1 in. 1-3 in. 3-7 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.