Avalanche forecast

Mt Hood

Feb 14 – 15, 2019Northwest Avalanche Center
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Avalanche danger

Sat
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
3 · Considerable
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Highlights

New and old avalanche problems have created a dangerous mix in the Mt. Hood area. Winds Thursday afternoon and night have created fresh wind slabs near and above treeline. The potential to trigger avalanches down several feet exists near and below treeline. Choose simple terrain to safely navigate this snowpack.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    1–2

    Fresh wind slabs will have formed Thursday and Thursday night on steep wind loaded slopes near and above treeline. Approach steep unsupported slopes with wind-drifted snow cautiously, feeling for firm or hollow sounding snow as a sign that wind slabs may be present. You can stay safe by traveling on ridges, wind-scoured areas and any slope less than 30 degrees. 

    In wind sheltered areas, storm slabs that formed over the last few days should be trending toward stubborn and unreactive. However, any avalanche triggered in the recent snow could result in a larger and more deadly persistent slab avalanche.

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Persistent slabs can break widely across terrain features, come down on top of you, and can be triggered from a long distance away. These avalanches are difficult to predict and can break wide and in surprising ways by wrapping around terrain features. Be especially suspicious near and below treeline where weak snow over a firm crust was most likely buried intact and recent avalanches have occurred. 

    If you hear large whumpfs, experience sudden collapses in the snowpack, see shooting cracks in relatively flat terrain or remotely trigger an avalanche, nature is trying to tell you deadly persistent slab avalanches are possible.

    Choose simple terrain that’s much lower angled and not connected to anything capable of producing a large avalanche. 

Discussion

Snow and Avalanche Discussion

Over 4 feet of snow fell during the 2/9-2/13 storm cycle. This new snow layered on top of a firm crust. Natural and skier triggered avalanches with the new snow and wind have tapered off during the week, but deeper avalanche problems have surfaced at the recent snow/old snow interface.

Several deep avalanches, averaging around 4 feet, were triggered Wednesday and Thursday by both skiers and explosives near and below treeline. Mt. Hood Meadows Patrol identified a layer of weak snow (1-2 mm facets) above a hard crust with at least one of these avalanches on an NE aspect.

Until we know more about the spatial distribution of this weak layer/crust combination, you will need to choose simpler terrain in all elevation bands.   

We've received a lot of snow over the last few days. The risk of tree well and snow immersion suffocation is real in the trees. Don't travel alone and always keep in contact with your partner. You can learn more about deep snow safety here.

Snowpack Discussion

Since February 8th, the mountains (and low elevation cities) of the Pacific Northwest have experienced cold and very stormy weather. Significant snowfall has added up in all forecast zones. Records from Snoqualmie Pass DOT avalanche workers back to 1973 show that February 11-12th set a record for the most snow recorded in a 24hr period at that location. The table below shows storm totals starting February 8th through the morning of the 13th 

5 day totals ending morning of Feb 13th

Water Equivalent (inches)

24hr storm totals

(inches)

Difference in Height of Snow (inches)

Hurricane Ridge

1.97

N/A

+ 30

Mt. Baker

1.94

44

 

Washington Pass

1.66

NA

+ 16

Stevens Pass

 

2.71

49

 

Snoqualmie Pass

3.91

80

 

Mission Ridge

1.86

38

 

Crystal

2.91

59

 

Paradise

4.55

N/A

 

White Pass

N/A

57 (4400ft)

+ 26 (5800ft)

Mt. Hood Meadows

4.70

43

 

Heavy precipitation brought many mountain regions to their tipping point. Avalanches ran readily with a peak of snowfall intensity. For Stevens Pass, Snoqualmie Pass, East Central, West South, Mt Hood, and possibly West Central zones we have good confirmation that this cycle happened from the night of February 11th through the 12th. In other zones, snow totals haven’t been significant enough for widespread avalanche cycles, or we lack data (like in the East South zone).

The high rates of precipitation drove avalanches in the storm snow. Notably, a persistent weak layer of facets and surface hoar was buried in most zones on February 8th. Storms produced a widespread and prolonged cycle of avalanches on the February 8th interface, involving a variety of aspects and elevations. Local ski patrols, highway workers, and backcountry travelers reported extensive avalanching with widely propagating crowns and very sensitive conditions. With less stormy weather, observers have just begun to get a sense of the extent of the avalanche activity. Triggering persistent slab avalanches will be a concern for backcountry travelers in zones where the February 8th weak layer is active for at least the near, if not distant future. Stay tuned for more updates.

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