Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 4th, 2020 - 7:00AM
Expires
Wed, February 5th, 2020 - 7:00AM
Forecaster
Ryan Van Luit
Avalanche risk The Bottom Line

Today the avalanche danger is CONSIDERABLE above 1,000′.  Human triggered wind slab avalanches are likely on steep slopes with previous or active wind loading.  If triggered, these wind slabs have the potential to overload buried weak layers and initiate a larger slab avalanche. Where wind slabs are not present, the persistent weak layers 2-3′ down are becoming more stubborn, but it still remains possible for a person to trigger a large slab avalanche on these layers.

Special Announcements

Tonight! Soldotna Avalanche Awareness. Join CNFAIC’s Aleph Johnston-Bloom for an evening avalanche awareness chat. 6-7:30 pm at Odie’s in Soldotna. FREE! Great information for those new to recreating in the backcountry and useful review for experienced folks. Geared to all modes of travel. Hope to see you there!

Avalanche Gear in Review with CNFAIC at Black Diamond.  Swing by Black Diamond in Anchorage for a discussion on avalanche rescue gear. Thursday, Feb 6th from 6-7:30pm. Free! CNFAIC forecasters Ryan Van Luit and Wendy Wagner will be there to discuss advances, common mishaps and answer any questions you may have about your own rescue gear. BYOG – Bring Your Own Gear! This is a great opportunity to test your own gear and ask questions.

Tue, February 4th, 2020
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
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.
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

Since yesterday morning we’ve had several hours of wind near 20mph with gusts to 47mph at the Sunburst weather station.  Winds as low as 12-15mph can transport low density snow.  Wind slabs continue to form in wind exposed areas throughout the region.  Where wind slabs exist on steeper slopes, it could be easy and likely for a human to trigger an avalanche.  Although we have a warming trend, the temperatures in the Alpine have remained below freezing helping maintain loose snow.  Our 3″ of new snow over night in addition to the snow from last week is still unconsolidated in most places and easily moves around with the variable winds.

It can be difficult to predict which slopes have formed wind slabs because the region has experienced winds from many different directions.  It’s essential to look for clues where wind slabs are forming, or have already formed.  If you see the winds depositing snow onto the lee of ridges or gullies, that’s a clear indicator a slab could be forming.  Scoured exposed areas can indicate loading to the leeward side.  Where visibility is low or you can’t see your entire route, remain aware of the snow beneath you –  you could be entering a wind slab if you feel stiffening of the snowpack, see rippling on the surface, see shooting cracks, or sense hollow drum-like sounds in the snow.  Choose routes with intention and don’t hesitate to adjust your plan.

Steady winds over the previous 30 hours capable of transporting loose snow.

 

This image is looking toward the northeast aspect of Magnum.  The visible scouring suggests easterly winds cross loaded many gullies on Magnum.  Winds from this direction could have easily loaded the common northwest uptrack.  2.3.2020  Photo: CNFAIC Archive

 

Cornices:  Cornices continue to form and could be touchy to human trigger as they build with new snow and wind transport.  As always, give cornices a wide margin.

Avalanche Problem 2
  • 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 snowpack structure contains weak layers formed before the storms last week.  We’re particularly keeping an eye on the MLK Jr facets and the NYE crust.  The incremental loading and wind transported snow naturally triggered avalanches last week – the MLK Jr facets and NYE crust were the suspected weak layers.  Our testing shows these layers are becoming more stubborn but it remains possible for a human to trigger a large avalanche in these layers 2-3′ down in the snowpack.  With time and our current warming trend, the chances increase for the top 2′ of snow to consolidate and become more cohesive.  These conditions could create a more distinct slab above these weak layers.

Additionally, If a wind slab is triggered, it could step down to initiate one of these layers deeper within the snowpack.

Loose Snow Avalanches:  On steep slopes with unconsolidated snow, watch for easily triggered loose snow sluffs.

Weather
Tue, February 4th, 2020

Yesterday: Cloudy skies with scattered snow showers. Winds were easterly 10-20 mph gusting into the 40s in the morning then decreased into the evening. Temperatures were in the mid to high 20’s. Snow accumulation overnight 1-3″.

Today:  Mostly cloudy skies with a high near 30°F and low around 23°F. Winds out of the Southeast from 5 -20 mph. New snow with accumulation of 2-4″ possible.

Tomorrow:  Cloudy skies with a high near 32°F and lows in the teens. Intermittent snow showers expected throughout the day and into the evening adding 1-3″ of snow.  Winds expected to be from the east 5 – 10 mph becoming light and variable into the evening.

PRECIPITATION 24-hour data (6am – 6am)
Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 28 2 0.2 58
Summit Lake (1400′) 28 1 0.1 20
Alyeska Mid (1700′) 28 4 0.31 56

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 ENE 16 47
Seattle Ridge (2400′) 23 ESE 11 26
Observations
Recent Observations for Turnagain Pass
Date Region Location
05/13/24 Turnagain Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South
05/13/24 Turnagain Observation: Turnagain Pass non-motorized side
05/12/24 Turnagain Observation: Warm up Bowl
05/07/24 Turnagain Observation: Turnagain Pass Wet Slabs
04/29/24 Turnagain Avalanche: Turnagain aerial obs
04/27/24 Turnagain Observation: Johnson Pass
04/23/24 Turnagain Observation: Turnagain Sunny Side
04/21/24 Turnagain Observation: Bertha Creek
04/20/24 Turnagain Avalanche: Spokane Creek
04/16/24 Turnagain Observation: Cornbiscuit
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.