THIS AVALANCHE ADVISORY EXPIRED ON January 19, 2019 @ 5:35 am
Avalanche Advisory published on January 18, 2019 @ 5:35 am
Issued by Ben Bernall - Kootenai National Forest

Kootenai

bottom line

The stable snow conditions of the past week will deteriorate as new snow falls on a bed surface of crust and well developed surface hoar. Thin, soft snow slabs will be wide spread and reactive Friday and likely to build through the weekend. Use caution in steep terrain and pay attention to the potential consequences of being caught in small slides as you travel. Avalanche danger has the potential to rise this weekend if predicted snowfall materializes!

How to read the advisory

The stable snow conditions of the past week will deteriorate as new snow falls on a bed surface of crust and well developed surface hoar. Thin, soft snow slabs will be wide spread and reactive Friday and likely to build through the weekend. Use caution in steep terrain and pay attention to the potential consequences of being caught in small slides as you travel. Avalanche danger has the potential to rise this weekend if predicted snowfall materializes!

3. Considerable

?

Above Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

?

Near Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

3. Considerable

?

Below Treeline
Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
    Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.
Avalanche Problem 1: Storm Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Snotel sites area wide are showing approximately 3-5" of new snow on average and Bear Mountain crushing the competition with 8" of fresh snow. This new snow is falling on a variety of very weak surfaces that have the potential to be highly reactive as the snowfall continues to build this weekend. The snow amounts as of Friday morning are less than what was predicted and slabs are likely to be thin, soft and benign in most locations. Expect them to become thicker, more cohesive and more reactive as more snow falls and temperatures rise on Friday and Saturday. 

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

New snow falling on crusts and weak surface hoar crystals will move easily in steep terrain. It is unlikely to bury you; but, it can push you down the hill and cause a loss of control. Pay attention to what is below you in steep terrain (cliffs, trees etc.)

Avalanche Problem 3: Persistent Slab
  • Type ?
  • Aspect/Elevation ?
  • Likelihood ?
    Certain
    Very Likely
    Likely
    Possible
    Unlikely
  • Size ?
    Historic
    Very Large
    Large
    Small

Both persistent slabs and deep slab weaknesses are lurking out there. Sugary snow can be found at the base of the snowpack in areas where coverage is thin and there are some thin faceted layers in the middle of the snowpack in the Purcell mountains. They continue to heal and I have observed little reactivity out of these layers in recent weeks.  Continue to pay attention to these possibilities during rapid warming trends and heavy loading events (rain/heavy snowfall) that will bring them back to life.

recent observations

It's all about the weather this weekend! We are set up perfectly to have very dangerous avalanche conditions, especially at treeline and below. There is a crust layer prevalent up to 5,500' across the forest, and there is well developed surface hoar on sheltered locations up to  6,500'. On southerly aspects the surface hoar is most likely to be found below 5,000' where the inversion layer kept it shaded from the sun. Above treeline we have a sun crust on southerly aspects. So, with a crust layer that is building facets below it and growing feathers on top of it, all we are missing is a cohesive slab of snow to put on it to create an avalanche. As of this Friday morning the snowfall totals are just not substantial enough to create a real problem in most locations. But, with the forecasted weather this is likely to change and we may be moving to HIGH DANGER if the storm snow continues to build. So, my best advice is to pay attention to the depth of snow as you travel this weekend and avoid being on or in steep terrain where even smaller slides can carry you into cliffs or trees that can beat you up. This past week conditions have been optimal for playing in steep terrain on all aspects and elevations, moving forward into the weekend it will be time to dial back your terrain selection and pay close attention to the new snow as it falls on very weak surfaces across the mountains. Click on the link below to see a short video displaying the conditions out there on Monday.

https://youtu.be/ZyBn8QEzXSw



Surface hoar crystals. Wednesday I observed crystals up to an 1" tall in the East Cabinets. 

 

Weather and CURRENT CONDITIONS
weather summary
Backcountry Forecast from NWS Missoula issued:
340 AM MST Fri Jan 18 2019

DISCUSSION: Scattered snow showers will continue to move across
the Northern Rockies through this afternoon. We will see an
increase in westerly winds in the higher terrain, particularly 
along the Continental Divide and Mission Mountains. Showers will
diminish by this afternoon. A weak disturbance will move into the
region again late tonight, and continuing through the day 
Saturday. Westerly winds will continue to increase, with the 
higher wind gusts confined along the Divide. Temperatures will be
slightly warmer for this event, with snow levels rising to around
4500 feet by the afternoon.

Another significant winter storm will move in late Sunday, 
through most of the day on Monday. Winds are not expected to be 
nearly as strong, though significant snow accumulations are 
likely. Northwest Montana, north of Highway 2, may miss out on the
heaviest precipitation with that storm.

Kootenai:
--------------------------- 5000-7000 FT ----------------------------
                      Today        Tonight      Sat      
Cloud Cover           85%          85%          90%      
Hi/Lo Temps           28 to 33     23 to 27     31 to 36 
Winds(mph)            SW 14G31     S 14G30      SW 22G52 
Precip Chc            80           90           100      
Precip Type           snow         snow         snow     
Liquid Amt            0.19         0.11         0.31     
Snow Ratio(SLR)       14:1         13:1         11:1     
Snow Amt(in)          2-8          1-3          3-7      

Snow Level            3000         2500         3500     
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.