Hatcher Pass Avalanche Center
Hatcher Pass

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Issued
Sun, December 26th, 2021 - 7:00AM
Expires
Mon, December 27th, 2021 - 7:00AM
Forecaster
Jed Workman
Avalanche Warning
Issued: December 26, 2021 12:00 pm
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

A backcountry avalanche warning and High Avalanche Danger will go into affect from 12pm today through 12 pm Monday.

The avalanche hazard will increase throughout the day and overnight.

Travel in avalanche terrain is not recommended.  Avalanches may run long distances.  Backcountry travelers should stay off of steep slopes and out from underneath slopes 30º or steeper.

NWS has issued a Winter Weather Advisory for today from Dec 26 at 6am through Dec 27 at 12am. A warm subtropical flow will deliver a “mess of precipitation” in the form of rain, freezing rain, rain and snow mix, snow and winds Sunday through Monday. Heavy precipitation and strong winds will overload a weak snowpack at all elevations resulting in natural avalanches large enough to bury a person. Large human triggered avalanches will be very likely.

Sun, December 26th, 2021
Upper Elevation
Above 3,500'
4 - High
Avalanche risk
Mid Elevation
2,500'-3,500'
4 - High
Avalanche risk
Low Elevation
Below 2,500'
4 - High
Avalanche risk
0 - No Rating
1 - Low
2 - Moderate
3 - Considerable
4 - High
5 - Extreme
Avalanche risk Avalanche risk Avalanche risk Avalanche risk Avalanche risk
Travel Advice Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features. Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern. Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding, and conservative decision-making essential. Very dangerous avalanche conditions. Travel in avalanche terrain not recommended. Extraordinarily dangerous avalanche conditions. Avoid all avalanche terrain.
Likelihood of Avalanches Natural and human-triggered avalanches unlikely. Natural avalanches unlikely; human-triggered avalanches possible. Natural avalanches possible; human-triggered avalanches likely. Natural avalanches likely; human-triggered avalanches very likely. Natural and human-triggered avalanches certain.
Avalanche Size and Distribution Small avalanches in isolated areas or extreme terrain. Small avalanches in specific areas; or large avalanches in isolated areas. Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas. Large avalanches in many areas; or very large avalanches in specific areas. Very large avalanches in many areas.
Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.
Likelihood of Avalanches
Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.
Size of Avalanches
Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word Size (D scale) Simple Descriptor
Small 1 Unlikely to bury a person
Large 2 Can bury a person
Very Large 3 Can destroy a house
Historic 4 & 5 Can destroy part or all of a village
More info at Avalanche.org

Our unstable snowpack continues to respond with avalanches each time it is loaded with precipitation. We expect this next round of precipitation to result in large natural avalanches and for human triggered avalanches to be very likely. Old avalanche paths may repeat.

Freezing levels may be as high as 3500-4000+’  today dropping this evening to 2500′. Winds may build to S-SW 28mph. Upper elevations may receive up to 6-10″ of snow by tommorow.

Widespread avalanches will be 1-3 feet deep, failing on old buried sugary snow (facets) on all aspects at all elevations on slopes 30º and steeper. It will be possible to remotely trigger large avalanches which may also trigger additional avalanches, making safe travel difficult to impossible in avalanche terrain. Predicting avalanche behavior will be difficult. Avalanches may run long distances, making even flat terrain, trails or roads susceptible to avalanche runout.

All week long we have been observing an unstable snowpack. Whumphing, shooting cracks and human triggered avalanches on all aspects and at all elevations demonstrate that the snowpack remains at a tipping point. We have seen a number of avalanches occur on slopes we do not usually see slide. Any time we see new or unusual avalanche behavior we need to employ more conservative decision making and take a large step back from unnecessary exposure.

More information in recent avalanche forecasts HERE.

NWS weather graphics for this storm

 

Weather
Sun, December 26th, 2021

NWS AVG Forecast here.

NWS Rec Forecast here.

NWS point forecast here.

State Parks Snow Report and Motorized Access information here.

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