Bulletin d’avalanche

Northern Wallowas

Wallowa Avalanche Center
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Danger d’avalanche

Alpin
2 · Modéré
Limite forestière
2 · Modéré
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 4 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

Triggering a 1.5-3' thick avalanche remains possible on some slopes. Avalanches are more likely on shady slopes facing E-N-W and could occur on both sheltered mid-elevation slopes and in wind-affected terrain. Recent winds have formed fresh, hard drifts that are likely to be small, but could be easy to initiate, with the potential of triggering persistent weak layers deeper in the snowpack.

This forecast is sponsored by the fine folks who brew good beer at Terminal Gravity in Enterprise, OR.

Problèmes avalancheux

  • Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    We have multiple known layers of buried surface hoar in the upper 3' of the snowpack in the Southern Wallowas.  There is some spatial variability, and this sensitive weak layer doesn't exist everywhere in the terrain.  There is a layer of surface hoar that was buried on Jan. 4th that produced a natural avalanche at Fish Lake on Jan 15th.  Another layer was buried on Jan 18th and has produced two snowmobile-triggered avalanches 1-3' deep this past week.  You can read a local rider's account of an avalanche his group triggered on the 24th.  Thanks to this rider for submitting observations this winter!

    You will likely not observe any Red Flags associated with the buried surface hoar, and it can be a very tricky weak layer.  A couple of options exist to increase your safety and decrease your chances of triggering an avalanche on this weak layer.

    1. Avoid slopes greater than 30 degrees near and below the treeline on W-N-E aspects. 

    2. Dig down into the snow to look for buried surface hoar, and conduct compression tests (CT) or extended column tests (ECT) to look for the initiation of a crack.  If you have a failure on the buried surface hoar, then you know it exists, is touchy, and should be avoided.  

    3.  If Step 2 is above your pay grade, or doesn't make sense, then sticking to Step 1 would be advisable.  

    You can read the observation from forecaster Victor McNeil on 1/25 and the reactivity of the buried surface hoar here.  

     

    (1/25/2023)

    Victor found the 1/18 layer of buried surface hoar reactive in his snowpack tests.  North aspect 7,000'.

    Photo: VM

  • Wind Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Likely
    Taille
    1–1.5

    Moderate westerly winds, 10-20mph and gusting in the 30's at ridgetop, have moved snow onto leeward terrain features at and near ridgeline. These pockets of hard drifted snow may be reactive to the weight of a rider. Wind slabs could be over a foot thick in places. An additional consideration is a wind slab triggered in the upper snowpack could step down to a persistent weak layer, like buried surface hoar, and produce a large destructive avalanche. Carefully evaluate N-E aspects in the alpine for reactive wind slab and buried surface hoar layers before committing to a slope. Wind slabs reactivity will increase throughout the day as the storm system drops up to 3" today and another 6" tomorrow.

    (1/25/2023)

    Winds from the N-NW-W were moving snow to S-E aspects on Wednesday.  The winds overnight have been mostly out of the west loading east-facing slopes.

    Photo: VM

Avalanche Discussion

We are in a tricky spot related to avalanche hazard right now. Throughout the ranges of northeast Oregon we have several widespread layers of buried surface hoar. The most reactive layer of buried surface hoar is down 1.5 to 2 feet in the snowpack. It was buried on 1/18. Buried surface hoar is a notorious persistent weak layer and has the added hazard of propagating fractures over large distances. What is tricky about surface hoar is that it isn't consistent across the snowscape. It largely lurks on more shaded and protected slopes. The likely place to find buried surface hoar is on E-N mid-elevation slopes below the ridgeline. Another tricky thing about surface hoar is that it is hard to see in the snowpack when digging a pit. The best way to test the upper snowpack for the presence of surface hoar is to do snowpack tests like the compression test (CT) and extended column test (ECT). If you get clean planar fractures on a thin weak layer, then you've likely found the buried surface hoar.

This doesn't mean surface hoar may not exist in the alpine or on more sunny slopes. That is what makes it tricky too. We are in a period right now where careful terrain evaluation and selection is needed to avoid the possibility of triggering a large and destructive avalanche. It is possible to trigger the surface hoar layer in the upper snowpack and have the avalanche step down into weaker layers in the lower snowpack. There are other buried weak layers deeper in the snowpack.

An example of this is a snowmobile triggered avalanche in the southern Wallowas on Tuesday that was 3' deep, 50 yards wide, and ran over a 100 yards. This slide was big enough to bury, injure, or kill a rider. If you are going into terrain steeper than 30 degrees, then you need to carefully evaluate the slope for buried surface hoar. And, if you don't know, then don't go. Keep your slope angles below 30 degrees to be extra safe.

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The 11 Annual Eastern Oregon Backcountry Festival is coming up.  Join us for our biggest fundraiser of the year February 3-5th. 

  • Friday, Feb 3rd: HQ in La Grande we are showing "Buried" the 1982 Alpine Meadows Avalanche.  Doors Open @ 5:30, Pie Auction 6:30, Movie starts at 7! Tickets are $5 at the door. There will be a pie auction, so if you have some fine baking skills and want to donate a pie - please email us.
  • Saturday, Feb 4th: Kip Rand Memorial Race registerhere.  Winners will receive $100 cash or an Anthony Lakes season pass for 23/24.  Mens and womens division.   (You must show up 15 minutes before the race starts at the EOBF tent near the rental shop. )
  • Snow safety clinics 10 AM Avalanche Companion Rescue Clinic.  Register here.  
  • 1 PM Snowpack Observation Clinic.Register here.  Space is limited, reserve your spot.  (You must show up 15 minutes before the clinics start at the EOBF tent near the rental shop. ) 
  • Bag of Hammers 3 PM at the Star Bottle Saloon.  Live auction and raffle.  
  • On Sunday you can join the forecasters for a tour into Angel Basin.  Register Here.  

If you aren't able to make it out for the events you can support the WAC by purchasing raffle tickets or bidding on items in our online auctionhere.  The online auction and raffle will run from Jan 20th at Midnight to February 5th at 8PM. 

Régions couvertes