Hatcher Pass Avalanche Center

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Sat, December 29th, 2018 - 7:00AM
Expires
Sun, December 30th, 2018 - 7:00AM
Forecaster
HPAC Staff
The Bottom Line

The avalanche hazard is MODERATE this morning and may rise to CONSIDERABLE this afternoon, depending on the amount of accumulated new snow  and strength of the wind today.

A moderate hazard for human triggered avalanches 1-4 feet deep at mid to upper elevations exists. Avalanches will be possible to trigger this weekend and tricky to predict. REMOTELY triggered avalanches will be possible in some locations. Warning signs, such as whumphing and shooting cracks, may NOT be present.

AVOID STEEP SLOPES WITH TERRAIN TRAPS, and choose slopes with gentle, fanning runouts.

Moderate avalanche hazard does NOT equal safe conditions everywhere. Deciphering the avalanche puzzle will be challenging, with large (D2), human triggered avalanches possible on a multitude of weak layers in the snowpack for an avalanche to choose to fail on.

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Sat, December 29th, 2018
Upper Elevation
Above 3,500'
Moderate (2)
Avalanche risk
Mid Elevation
2,500'-3,500'
Moderate (2)
Avalanche risk
Low Elevation
Below 2,500'
Low (1)
Avalanche risk
Upper Elevation
Above 3,500'
Avalanche risk
Moderate (2)
Mid Elevation
2,500'-3,500'
Avalanche risk
Moderate (2)
Low Elevation
Below 2,500'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

A remotely triggered avalanche occurred yesterday, 12/28, on the SE face of Hatch Peak. See more details in the observation HERE.

A small, human triggered wind slab avalanche was reported on Sunday 12/23. See observations HERE.

No other avalanches have been reported.

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
Persistent Slabs
Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.
More info at Avalanche.org

Stability has increased very slowly over the last two weeks, but significant flaws in the architecture of the snowpack remain. While the probability of triggering an avalanche has decreased, the consequences have not. Avalanches will be possible, large enough to bury, injure to kill a person, and difficult to predict. Remotely triggered avalanches will be possible in some locations. Avoid terrain traps.

MODERATE avalanche hazard at mid to upper elevations for persistent slabs, 2-4 feet deep, exists this morning on all aspects, on slopes 35º+, for avalanches up to size D2. The snowpack has had a long time to adjust during an extended, mild weather pattern, however, it will still be possible to human trigger avalanches and in some locations it will be possible to remotely trigger avalanches. Predicting where and when these avalanches will occur will be difficult. Weak layers in the snowpack containing basal facets, a crust/facet combination near the base of the snowpack, mid-pack facets and buried surface hoar near a thin, old rain crust will continue to be possible human trigger. Surface hoar can be particularly difficult to find in snowpits, and located in a patchy distribution, making predicting the location for avalanche activity on this layer extremely difficult.

In a remotely triggered avalanche yesterday on Hatch Peak, with no involvement, the third skier triggered a slab avalanche large enough to deeply bury a person in a severe terrain trap, from 350 feet away. Remotely triggered avalanches are very dangerous, you may be able to trigger them from connected, adjacent terrain, or from the flats below. You do not have to be on the actual slope to trigger it.  We suspect surface hoar was the initial weak layer to be triggered in this avalanche. With so much uncertainty and difficulty predicting where and when avalanches will occur, choose safer terrain to minimize your exposure. Avoid terrain traps where the consequences of any size avalanche will be compounded. Choose terrain with gentle fanning runouts.  

Pictured below: remotely triggered avalanche on 12/28/2018. See previous forecast for more details.

 

Weather
Sat, December 29th, 2018

NWS is calling for 3-4″ of new snow, cool temps and low wind speeds.

If we get more snow or stronger wind than predicted, expect the avalanche hazard to increase abruptly to CONSIDERABLE.


NWS Rec Forecast HERE


State Parks Snow Report and Motorized Access information HERE

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