Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, December 6th, 2020 - 7:00AM
Expires
Mon, December 7th, 2020 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

Today’s avalanche danger is CONSIDERABLE in the Alpine, and MODERATE at and below Treeline. Human-triggered wind slab avalanches will become likely as a storm moves into the area throughout the day. Pay close attention to changing conditions as winds and new snowfall build sensitive slabs, especially later in the day. Be on the lookout for clear indicators of increasing avalanche danger, and get out of harm’s way by sticking to low angle terrain out of the way from any steeper slopes overhead.

SUMMIT LAKE: The snowpack in the Summit Lake area is generally thinner and weaker than the rest of the advisory area, making it easier to triggering a deep slab avalanche near the ground. Be extra cautious with your terrain choices down here, and avoid steep, rocky terrain where these avalanches will be most likely.

Sun, December 6th, 2020
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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.
Recent Avalanches

• A snowboarder triggered an avalanche near the ground, 1.5-4′ deep, on a east-southeast facing slope on Silvertip yesterday. Nobody was caught or carried.
• During the past few days of clear weather, multiple skiers and riders noted widespread activity during or immediately after the previous (11/30-12/1) storm. More photos here, here, and here.

Silvertip. A snowboarder triggered this avalanche near the ground on Saturday (12/5). The slab was 1.5-4′ deep, and it failed in weak snow near the ground. Nobody was caught. Photo: George Creighton. 12.05.2020

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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

The mountains will receive 4-6” new snow by the end of the day and another 4-6″ tonight, which will fall on a layer of weak facets and surface hoar. Since midnight, sustained easterly ridgetop winds of 20-33 mph with gusts to 51 mph have already started moving existing snow into sensitive slabs, and the new snow will provide more ammunition for slab building. By the end of the day, we can expect to see fresh wind slabs 1-2’ deep on top of weak snow. Mountain temperatures are going to rise to right around freezing during the storm, so this next pulse of snow is going to come in upside down, with heavier snow sitting on top of lighter snow.  At elevations up to 2500 feet, this suspect setup will be sitting on a low-friction rain crust, which will act as an optimal bed surface for avalanches failing in the new snow. As the storm moves into our area through the day, it will become easy to trigger an avalanche, especially on wind loaded slopes.

It will be important to pay attention to changing conditions today, and to be on the lookout for clear signs that the avalanche danger is increasing. These can be in the form of cracks shooting out from your snowmachine or skis, a collapse or ‘whumpf’ below your feet, and recent avalanches. If you start to notice any of these signs, it is time to move to low angle terrain (less than 30 degrees), avoiding runout zones below steeper slopes.

Click here for a video discussing the conditions in the Summit Lake area on Friday.

Avalanche Problem 2
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.
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

Weak, faceted snow persists at the bottom of the snowpack at many locations throughout our advisory area, and we cannot rule out the potential for large avalanches failing at the ground. Although it is slowly becoming less likely to trigger an avalanche in this deep persistent weak layer, we are still seeing reports of poor structure, and occasional unstable test results within this weak layer. In areas with a thinner snowpack, this weak layer is still collapsing under the weight of a person. Thursday’s skier-triggered avalanche on Tincan, and yesterday’s snowboarder-triggered avalanche on Silvertip should serve as reminders that there is a lingering possibility of triggering a deep slab avalanche. Avoid steep, rocky terrain with a thin snowpack, as this will be the most likely place to trigger a large avalanche near the ground.

Weather
Sun, December 6th, 2020

Yesterday: Clear to partly cloudy skies, light winds, and high temps in the single digits made for excellent (if not a bit chilly) riding conditions yesterday. Easterly winds picked up around midnight last night, with sustained speeds of 20-33 mph and gusts to 51 mph. It started snowing early this morning, with 2″ on the ground at 6:00 am.

Today: Snowfall will continue today, with 4-6″ expected during the day and another 4-6″ tonight. Easterly winds will calm down slightly, with sustained speeds of 10-20 mph and gusts to 30 mph. Mountain temperatures are in the upper 20’s this morning, and will rise to low 30’s through the day and into tonight. Rain/snow line is expected to rise to 500 feet today, and we could see rain up to 1000 feet tonight.

Tomorrow: Snow will continue tomorrow, with another 2-5″ expected. Temperatures should hover right around freezing, with easterly winds blowing 20-25 mph starting tonight.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 16 1 0.1 55
Summit Lake (1400′) 4 0 0 21
Alyeska Mid (1700′) 10 2 .12 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 14 N 10* 51
Seattle Ridge (2400′) 14 S 3 20

*Easterly winds have picked up to 20-33 mph, with gusts to 51 mph since 2:00 AM this morning.

Observations
Recent Observations for Turnagain Pass
Date Region Location Observer
10/27/24 Turnagain Observation: Tincan Michael Kerst
10/21/24 Turnagain Observation: Turnagain Pass Road Observation Trevor Clayton
10/19/24 Turnagain Observation: Tincan – Below Todds Run Andy Moderow
10/18/24 Turnagain Observation: Taylor Pass Eli Neuffer
10/15/24 Turnagain Observation: Tincan Common John Sykes Forecaster
10/14/24 Turnagain Avalanche: Tincan CNFAC Staff
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South H Thamm
05/13/24 Turnagain Observation: Turnagain Pass non-motorized side Amy Holman
05/12/24 Turnagain Observation: Warm up Bowl Tony Naciuk
05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs A S
Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.


Subscribe to Turnagain Pass
Avalanche Forecast by Email

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.
Become a Member
If you think a public avalanche center is important please support our organization.
Donate Now
Become a Sponsor
Supporting the CNFAIC proudly shows that your business or organization values the safety of our snow sports community.
Become a Sponsor