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BACKCOUNTRY AVALANCHE FORECAST

STEVENS PASS

ISSUED
Friday, January 17, 2020 - 6:24PM Fri, Jan 17, 2020 - 6:24PM
AUTHOR
Andrew Kiefer
THE BOTTOM LINE

Heavy snow, strong winds, and rising temperatures will create dangerous avalanche conditions Saturday. Give the new snow time to stabilize, and avoid travel on or below large open slopes 35 degrees and steeper.

AVALANCHE DANGERi

Saturday, January 18, 2020
Above Treeline Considerable (3)
Near Treeline Considerable (3)
Below Treeline Considerable (3)

OUTLOOKi

Sunday, January 19, 2020
Considerable (3)
Moderate (2)
Moderate (2)

OUTLOOKi

Sunday, January 19, 2020
3 2 2
Danger Scalei
  • Low (1)
  • Moderate (2)
  • Considerable (3)
  • High (4)
  • Extreme (5)

FORECAST DISCUSSION

A significant winter storm will impact Stevens Pass over the next 24 hours bringing increasing avalanche danger. Danger should peak mid to late morning when the strongest winds and highest snowfall rates combine with a slight warming trend to form unstable slabs. Additional snow will add to the already impressive snow totals from the past week. Ongoing storms since the New Year began have dramatically improved coverage at low elevations, and the current snow depth at Stevens Pass is over 120% of normal for mid-January (Snow Depth Climatology).

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
Photo for Storm Slab

Example Shooting Crack (1/17/2020)

Over the next 24hrs, new snow and strong winds will build fresh slabs atop colder, lower density snow from the past few days. Avalanches will be most sensitive to human triggers during periods of intense precipitation. Expect thicker and more reactive slabs in wind affected terrain at upper elevations. Also, keep in mind that the added weight of incoming snow will further test an older storm interface deeper in the snowpack buried on January 10th.

Seek out small, inconsequential slopes to test how new snow is bonding to itself and the old snow surface. Watch for obvious signs of unstable snow like shooting cracks, collapses, and recent avalanches. Avoid wind loaded and convex slopes steeper than 35 degrees. Give the new snow time to stabilize and seek out supported and lower angled terrain. Additionally, hazards exist even away from avalanche slopes like tree well falls and snow immersion suffocation. Make sure you’re informed and travel with a partner (www.deepsnowsafety.org).

 

January 16th, 2020 (The regional synopsis is updated every Thursday @ 6 pm)

In the past week and a half, there have been five avalanche fatalities in three separate accidents in the US. One occurred near Kellog, ID and another outside of Baker City, OR. Local avalanche centers will perform accident investigations including final reports. You can find preliminary accident information at avalanche.org.

From January 9th to 16th the Pacific Northwest slid into deep winter. A cold and snowy regime brought a nearly continuous barrage of storms through the area. Temperatures bottomed out as modified arctic air made its way south from interior Canada, and many stations recorded the lowest temperatures of the season so far. A snowpack has been growing at lower elevations due to some lowland snow on both sides of the Cascades.  NWAC’s snow depth climatology report shows most stations have surpassed average depths on the ground for this time of year. Quite the comeback from two weeks ago, when most were at 25-64% of normal. 

Location

Total Snow Depth (in) 1/8/20

Total Snow Depth (in) 1/16/20

Hurricane Ridge

51

91

Heather Meadows Mt Baker

95

126

Stevens Pass

63

85

Snoqualmie Pass

33

77

Mission Ridge Mid Mtn

18

28

Crystal Mt Green Valley

66

92

Paradise Mt Rainier

105

138

White Pass Upper

69

110

Timberline

57

118

Mt Hood Meadows

53

98

Snow depths continued to rise. Total snow depths doubled in some locations.

The mountains went through a period of prolonged dangerous to very dangerous conditions as the snow kept coming. Many locations picked up over a foot of new snow per day for a number of days in a row, and storm slab instability was widely experienced across the region. At times, instabilities within new snow layers were very reactive, and you didn’t have to do much to provoke an avalanche. Many people triggered small to large soft slab avalanches, even well below treeline. The cold temperatures tended to preserve these instabilities longer than usual during this time. 

Small ski triggered storm slab near Mt Hood Meadows. January 11, 2020. Scott Norton photo.

This cold, low density snow was also susceptible to wind drifting as westerly winds buffeted the alpine zone from the 8th to the 15th. On the 15th the mean winds shifted, and a south and east wind event disturbed the powder on open, exposed terrain near the passes and at upper elevations throughout the region. This created wind slab problems in some unusual locations.

Wind slabs formed over the low density powder snow. Mt Baker Backcountry. January 15, 2020. Zack McGill photo.

Trailbreaking in undisturbed snow was often very deep and difficult. In most places at any point in the week you could step off your skis or machine and sink in up to your chest in deep powder snow. The deep snow presented hazards of its own such as tree wells, and made it very easy to get stuck on a machine or lose a ski. Many folks experienced excellent, deep powder conditions and stuck to conservative terrain choices. 

-MP

A cold winter’s day over the Chiwaukum Range, from Stevens Pass. Matt Primomo photo.

No Corresponding Mountain Weather Forecast Available