Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Tue, February 18th, 2020 - 7:00AM
Expires
Wed, February 19th, 2020 - 7:00AM
Forecaster
Ryan Van Luit
Avalanche Warning
Issued: February 18, 2020 6:00 am
Travel in avalanche terrain is not recommended. Avoid being on or beneath all steep slopes.
Avalanche risk The Bottom Line

We have issued a BACKCOUNTRY AVALANCHE WARNING through the National Weather Service for the Turnagain Pass area and surrounding mountains.

Heavy snowfall, rain, and strong winds have created a HIGH avalanche danger in the mountains surrounding Turnagain Pass, Girdwood Valley, Portage Valley, and areas on the Kenai including Summit Lake and the Seward zone. Dangerous avalanche conditions are expected on all slopes 30 degrees and steeper – including runout zones. Avalanches are expected to release naturally, be easily triggered by people and send debris to valley floors. Travel in avalanche terrain is NOT recommended. Areas with steep slopes above should be avoided, such as the Byron Glacier Trail and the Seattle Ridge Uptrack. Even small terrain features could act as deadly traps.

SUMMIT LAKE TO SEWARD REGION: Expect the avalanche danger to remain elevated due to warm temperatures, strong winds and recent precipitation.

*Roof Avalanches:  Warming temperatures and rain could cause roofs to begin to shed their snow. Pay special attention to children, pets and where you park your car.

Special Announcements

Increased avalanche danger exists region-wide, outside of our forecast area. Very strong wind was seen overnight and the NWS has issued a winter storm warning for Chugach State Park through tomorrow morning.

Tue, February 18th, 2020
Alpine
Above 2,500'
4 - High
Avalanche risk
Treeline
1,000'-2,500'
4 - High
Avalanche risk
Below Treeline
Below 1,000'
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
  • Storm Slabs
    Storm Slabs
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Storm Slabs
Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

In the last 24 hours temperatures have increased to above freezing, pushing our snow line to 1300′.  The mountains around Girdwood have seen over 1″ of storm water in this time while Turnagain pass is showing 0.3″ of storm water.  These numbers could translate to 12-24″ of snow where it’s cold enough to accumulate.  We’re expecting up to another 1″ of storm water, which could mean an additional 12-24″ of snow in the Alpine in the coming 24 hour period.

When we add these warm temperatures and precipitation with steady winds ranging from 20-40mph gusting up to 83mph, we’ll have storm snow issues, wet avalanches concerns, and large wind slabs developing.

Natural activity is expected throughout the day with continued weather impacting our region. This includes large natural slab avalanches 2-5’ thick in the alpine and wet avalanches below 2000’ due to heavy rain and above freezing temperatures. Avalanche activity could run the full length of a slope, thus it will be important to stay off any slopes greater than 30 degrees and avoid being near any runout zones today. This set up could be a hazard even in the Tincan Trees where small terrain features could have high consequences. In channeled terrain an avalanche from above could easily entrain wet snow in the lower elevations and run further than expected. This will be especially important in places like Portage Valley, Johnson Pass trail and the flats below Seattle Ridge.

Avoidance of avalanche terrain is the only way to “manage” this problem today.  It’s a great day to hit the slopes of Alyeska, or do your taxes!

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 layers of facets and buried surface hoar within the snowpack continue to be a concern throughout the region.  With new snow accumulating over the existing snowpack, the region-wide Persistent Slab is transitioning into a Deep Persistent Slab. Significant weak layers now sit at least 3′ deep in the snowpack in many places.  Will this new load of snow and rain tip the balance and cause widespread avalanches?  Today avalanches occurring in the upper layers of storm snow have the potential to step down and release deeper layers. If this does happen the volume will be large and could run long distances.

Travel in avalanche terrain is not recommended today including being in the runout of a steep slope.

Weather
Tue, February 18th, 2020

Yesterday: Cloudy skies with 5-10″ of snow accumulation overnight.  Winds were easterly at 20-30 mph gusting into the 50s. Temperatures ranged from the low 30°Fs to the high teens. Winds and precipitation intensity increased overnight and temperatures climbed into the 20°Fs and 30°Fs. An inch of storm water (10-12″ of snow) was recorded with rain at sea level and as high as 1000-1300′.

Today: Heavy snow and rain continue today into tomorrow with a snow line forecast at 1300′. Additional snow accumulations ranging from 12-24″ are expected in the Alpine.  Winds will remain strong in the morning and slowly diminish later in the day.  Temperatures at sea level will hover in the 30°Fs to low 40°Fs during the day and shift into the upper 20°Fs in the evening.

Tomorrow: Tuesdays storm is expected to taper by tomorrow before the next storm picks up Wednesday evening.  Temperatures are likely to cool into the 20°Fs with southerly winds ranging from 10-30mph.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 3 0.33 64
Summit Lake (1400′) 33 2 0.3 26
Alyeska Mid (1700′) 29 8 1.1 68

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 ENE 37 83
Seattle Ridge (2400′) 25 SE 18 35
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.