Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, January 26th, 2018 - 7:00AM
Expires
Sat, January 27th, 2018 - 7:00AM
Forecaster
Heather Thamm
Avalanche risk The Bottom Line

Today there is CONSIDERABLE  avalanche danger above 1000′ (in the Alpine and Treeline zone) where triggering a storm slab 1-2 feet deep will be likely in areas exposed to recent wind. If ridge top winds remain elevated today, natural slab avalanches and loose snow avalanches will be possible. Evaluate snow conditions as you move up in elevation and keep your terrain choices mellow, less than 30 degrees. Cautious routefinding, and conservative decision making are essential. In places protected from wind triggering a loose snow avalanche will be likely on steep features. Also don’t forget – high in the alpine above 3000′, Deep Slab avalanche (3-8+ feet) will be stubborn to trigger, but could have high consequences.  

Below Treeline (1000′) and in places protected from recent wind the avalanche danger is MODERATE where triggering a storm slab 1-2 feet deep or loose snow avalanche is possible. Be aware of runout zones, terrain traps and other people around you.  

Special Announcements
  • Tomorrow (Saturday) January 27th, 11:00 am – 12:30 pm:  Join CNFAIC forecasters for a FREE hands-on and in-the-snow avalanche beacon practice!!  This 1.5 hour  informal rescue practice is geared for all user groups. Grab your friends and join us  before hitting the hills!! Great intro or refresher!  Hosted by the Anchorage Snowmobile Club!  At  Turnagain Pass (motorized parking lot) €“ Look for the blue CNFAIC snowmachine trailer.
  • Roads and parking areas in Turnagain Pass and Portage Valley may take awhile to clear. Be courteous to plow drivers and their efforts to clear snow from these areas.  

Fri, January 26th, 2018
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
  • 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

A sneaky storm overnight produced an estimated 10-20”  (0.5”-1.0” water weight) of low-density snow across our region and ridge top winds increased into the 20-40mph range last night. This snow started out with light wind and single digit temps, but temperatures suddenly bumped into the 20F’s along with a spike in Easterly winds. This means storm slabs in the alpine could range from 1-2’ deep, have an upside down quality, and could be easy to trigger. This snow fell on 5” of low density snow that was covering a widespread layer of buried surface hoar and near surface facets. Below 2000′ these layers are sitting on a slick bed surface crust. Bonding along these older interfaces is expected to be poor. Triggering a storm slab could be big enough to bury a person, but will depend on how deep the snow in the area you are traveling. The deeper the new snow the bigger the consequence. Clearing skies combined with high quality skiing/riding conditions may be hard to resist. Evaluate snow conditions as you move up in elevation and avoid terrain traps and being on or underneath larger steep slopes. Triggering a storm slab could run farther and faster than expected, which is the nature of cold snow. Shooting cracks, ‘whumpfing’, and any avalanche activity will be obvious clues that the snow is unstable.  Be aware of other groups of people in the same area and practice safe travel protocols. 

Notice the sudden spike in temps and winds last night. This combined with an estimated 10-20″ of new snow are all red flags warning signs that avalanche danger is elevated. 

Web cam at DOT weather station is one of the only views of how much snow has accumulated overnight at Turnagain Pass.  24 hr snow water equivelent was not reporting at this site this morning. 

 

Avalanche Problem 2
  • Dry Loose
    Dry Loose
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Dry Loose
Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

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 places protected from the winds loose snow avalanches ‘sluffing’ will be likely on steep terrain features. Similar to a storm slab, this dry loose snow could run faster and farther than expected. This hazard could bury a person in a terrain trap or underneath a large slope. 

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

Unfortunately, the snowpack structure above 3000′ is composed of a hard slab (3-8 feet thick) sitting on a variety of weak layers in the mid pack (including buried surface hoar) and old November facets near the ground. Deep persistent slab avalanches remain a concern on these upper elevation slopes. Triggering a deep slab is becoming difficult, but is still possible. The most likely trigger spots are thin areas in the snow cover, often near rocks, or where the slope rolls over.  South of Turnagain Pass the snow cover is thinner, triggering a slab in this area could be more likely as well. Remember, this is a ‘low probability, high consequence’ situation. This issue can simply be avoided by sticking to terrain below 3000’ (which is a good portion of terrain at Turnagain) and is secondary to triggering a storm slab avalanche today. Choosing low-consequence terrain in the Alpine is recommended. 

 

Weather
Fri, January 26th, 2018

Yesterday a storm brought an estimated 10-20 € of snow across our region. Center Ridge weather station picked up 0.5 € of water and Alyeska Midway, 0.7 € water, and Portage Valley (at Bear Valley) had 1.1 € of water. This storm also started light winds and single digit temperatures. Yesterday evening temperatures suddenly increased into the 20F’s and Northeasterly ridge top winds picked up into the 15-40mph range yesterday evening and overnight.  

Today ridge top winds are expected to decrease, but could range from 5-20 mph from the East. Skies could range from partly cloudy to overcast and temperatures are expected to be in the 20F’s. Scattered snow showers are expected this evening.

Snow showers are expected through Saturday morning with only a few inches of accumulation expected. Temps will be in the teens (F) and moderate to strong winds are in the forecast for the weekend. In the long term forecast there is talk of warming temps and a chance for more precipitation mid week.  

*Snow totals are estimated from the Center Ridge Weather Station. They could be deeper, but snow depth sensor was not reading depths as of 6am.  

Web cam at Bear Valley in Portage. Looks like almost a 1.5′ of snow in Portage overnight.  

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

  Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 11   *10   .5   *67
Summit Lake (1400′) 6   7   .3   22  
Alyeska Mid (1700′) 10   12   .7   59  

RIDGETOP 24-hour data (6am – 6am)

  Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 5   ENE   13   44  
Seattle Ridge (2400′) 3   E    8 21  
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
02/19/24 Turnagain Avalanche: Base of Seattle Ridge
02/18/24 Turnagain Observation: Lynx creek
02/18/24 Turnagain Observation: Tincan Trees
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.