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Sat, January 1st, 2022 - 7:00AM
Sun, January 2nd, 2022 - 7:00AM
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′, where moderate NW winds will transport the 3-5″ of new snow into fresh wind slabs up to 1′ deep. Human triggered avalanches are possible on wind loaded features and avalanches could run fast on an icy bed surface. Look for signs of wind transport on the snow surface, hollow feeling snow, and shooting cracks to identify wind loaded features and use test slopes to determine how reactive wind slabs are before stepping into exposed terrain.

Below 1000′ the avalanche danger is LOW, where winds should be weaker and triggering an avalanche is unlikely.

SUMMIT LAKE / LOST LAKE: Stronger winds could impact these areas more than the forecast zone and cause more widespread wind slabs.

Sat, January 1st, 2022
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
Wind Slabs
Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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

Happy New Year!!!

The mountains got a much needed refresh of snow yesterday, with 3-5″ falling throughout the forecast area. The depth of the new snow was on the lower end towards Johnson Pass trailhead and on the higher end north of Turnagain Pass. Today outflow winds are picking up out of the NW and temperatures are dropping. Outflow winds can affect some areas of the forecast zone more than others, and Seattle Creek drainage along with areas on the southern end of the forecast zone like near Johnson Pass trailhead tend to see higher wind speeds. The primary concern is fresh wind slabs forming in areas exposed to the wind. Thanks to the melt/rain crust from last week there is not that much snow available to be transported by the wind, so wind slabs should be on the small side at up to a foot deep. It is likely that the new snow will not bond well to the icy surface that it fell on, which could make fresh wind slabs touchy to human triggers today. Look for signs of wind transport on the snow surface, hollow feeling pillows of snow, and shooting cracks or collapsing to identify recently wind loaded areas.

Even though we expect wind slabs to be on the small side today, the icy bed surface will make them run fast and could make it difficult to arrest or get out of the way of a flowing avalanche. Use caution in exposed terrain because the underlying crust is quite slick and firm in some areas. There is also a possibility that isolated pockets of surface hoar developed prior to the latest storm, which would make triggering an avalanche even easier and could lead to wider than expected propagation. So far we have only seen this in a few specific locations and don’t anticipate that it is a widespread problem.

3-5″ of new snow over variable melt/rain crust. The thickness of the crust is variable but overall it seems like it is more supportable at higher elevations. Photo 12.31.21

Additional Concern
  • Deep Persistent Slabs
    Deep Persistent Slabs
Deep Persistent Slabs
Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.
More info at Avalanche.org

We checked in on the November faceted layer on Tincan yesterday and found that it continues to gain strength and be mostly unreactive in stability tests. The hardness of the weak layer is increasing and the faceted grains are continuing to round. Reports of avalanche activity on this layer have also stopped since the melt/rain crust on the snow surface froze in the middle of the weak.  In areas with a thicker slab on top of the faceted layer and where the melt/rain crust is thicker it is very unlikely to trigger an avalanche on this old layer of facets. However, on the southern end of the forecast area it is feasible to find a location where the snowpack has a combination of a thin slab on top of the facets (< 2′ deep) and a thin melt/rain crust that could make it possible to trigger a deeper avalanche 2-5′ deep. We are optimistic that this layer is becoming dormant, but recognize the outside chance that it could cause a large avalanche if the perfect combination of snowpack conditions exists somewhere.

Snowpack structure from 1600′ on Tincan. Photo 12.31.21 

Sat, January 1st, 2022

Yesterday: Moderate snowfall throughout the day with total storm accumulations around 3-5″. Light to moderate winds which switched from a E direction during the snowfall to a W direction at around 4 pm. Temperatures stayed in the teens to low twenties yesterday and started to drop in to the low teens and single digits overnight.

Today: Another round of NW outflow winds are setting up today as the low pressure system from yesterday’s snowfall moves out of the area. Temperatures should drop into the single digits and winds will pick up to the 15-30 mph range. In areas exposed to local gap winds the speed could be higher, with gusts up to 60+ mph. There is a chance of snow showers today but no new accumulation is expected.

Tomorrow: Temperatures will continue to drop tonight and into tomorrow, with highs in the positive and negative single digits expected tomorrow. Winds will remain out of the NW tomorrow but look to decrease in speed. Cold temperatures should ease off a bit early next week but no new snow is in the forecast through the middle of the week.

PRECIPITATION 24-hour data (6am – 6am)

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 23 2 0.2 66
Summit Lake (1400′) 19 2 0.2 24
Alyeska Mid (1700′) 21 1* 0.1 39*

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 12 E until 1600 Then W 7 29
Seattle Ridge (2400′) 16 SE until 1600 then NW 4 14
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This is a general backcountry avalanche advisory issued for Turnagain Arm with Turnagain Pass as the core advisory area. This advisory does not apply to highways, railroads or operating ski areas.