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BACKCOUNTRY AVALANCHE FORECAST

WEST SLOPES SOUTH - SOUTH OF I-90 TO COLUMBIA RIVER

ISSUED
Wednesday, December 11, 2019 - 6:14PM
AUTHOR
Andy Harrington
THE BOTTOM LINE

Conditions are changing in the mountains. Temper your excitement, choose conservative terrain, and ease into winter. The first major snow event of the season will bring several feet of snow, particularly in areas near Paradise, and increase the avalanche danger.

AVALANCHE DANGERi

Thursday, December 12, 2019
Above Treeline Considerable (3)
Near Treeline Considerable (3)
Below Treeline Moderate (2)

OUTLOOKi

Friday, December 13, 2019
Considerable (3)
Considerable (3)
Moderate (2)

OUTLOOKi

Thursday, December 12, 2019
3 3 2
Danger Scalei
  • Low (1)
  • Moderate (2)
  • Considerable (3)
  • High (4)
  • Extreme (5)

FORECAST DISCUSSION

Paradise is forecasted to receive more water than other areas in the zone, but the story remains the same throughout. A variable early season snowpack, with recent avalanche activity, will become buried throughout the forecast period. A natural avalanche cycle is possible during the height of the storm at higher elevations. Be conservative and ease into terrain by starting with small test slopes and evaluating what is happening with the snow. Tomorrow will be stormy with low visibility, it is not a good day to travel under features that you cannot see the top of. Recognize that until this storm, very low snow conditions existed, and early season hazards will persist despite the new snow.

This storm has the ability to change the avalanche danger quickly over space and time. With periods of high precip rates and fluctuating freezing levels, pay attention to how the storm snow sets up. Is it rightside up or upside down? Are there interfaces within the storm snow as winds or precip rates change? As the snow piles up, a day that starts out as moderate can develop into considerable quickly. Likewise, with high amounts of water forecasted, High avalanche danger could be reached by day’s end in the Paradise area. Anchors will become buried, and slab depth will increase throughout the storm. Pay attention to wind affected snow and look for collapses, cracks, and recent avalanches.

Lots of early season hazards at Rainier before the storm. Photo: Dallas Glass 12/8/19

AVALANCHE PROBLEM #1i

  • Storm Slab

    Avalanche Problemi
  • Above Treeline
    Near Treeline
    Below Treeline
    Aspect/Elevationi
  • Unlikely
    Possible
    Likely
    Very Likely
    Almost Certain
    Likelihoodi
  • Small (D1)
    Large (D2)
    Very Large (D3)
    Historic (D4-5)
    Sizei

A few feet of new snow is forecasted to fall, making the formation of storm slabs likely on all aspects at all elevations. Slabs as deep as 3 feet, more than enough snow to bury a person, are expected. Changes in temperature, precipitation rate, and wind affect the bonding of snow. These bonds, whether in new snow, or at the old snow interface, will dictate the reactivity of storm slabs. Avoid traveling on slopes greater than 35 degrees when you find strong snow over weak snow. Below treeline, storm snow will be falling on a thinner existing snowpack, minimizing the avalanche danger.

 

Regional Synopsis Coming Thursday, December 12, 2019
 

No Corresponding Mountain Weather Forecast Available