Turnagain Pass RSS

Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Sun, December 17th, 2023 - 7:00AM
Expires
Mon, December 18th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE today, and it is likely a person will be able to trigger an avalanche 1-3 feet deep in new and windblown snow from last night. This round of snow is adding more stress to a deeper weak layer of snow buried near the Thanksgiving crust, increasing the chances of larger avalanches failing deeper in the snowpack. Travel cautiously today, and be especially careful in areas that received the most snow or on slopes with dense wind slabs on the surface.

Roof Avalanches: The latest storm finished with rain in Girdwood, saturating feet of snow that has piled up on roofs over the past week and increasing the chances of roof avalanches. Be careful when you are entering or exiting buildings, keep an eye on children and pets, and be mindful of where you park your vehicles.

Special Announcements

Hatcher Pass:  The Hatcher Pass Avalanche Center has issued a Sunday morning forecast due to stormy weather and dangerous avalanche conditions. See it HERE.

Headed to Chugach State Park, Summit, or Seward? Be sure to check our new Weekend Avalanche Outlook products for these zones. You can find them by clicking a zone on the map on our homepage, or by using the dropdown ‘Forecast’ menu and selecting a zone.

Sun, December 17th, 2023
Alpine
Above 2,500'
3 - Considerable
Avalanche risk
Treeline
1,000'-2,500'
3 - Considerable
Avalanche risk
Below Treeline
Below 1,000'
3 - Considerable
Avalanche risk
Mon, December 18th, 2023
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
Mon, December 18th, 2023
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

The most recent observed avalanche activity was a widespread cycle of natural avalanches that occurred during Wednesday and Thursday. It is likely there was another natural cycle during last night’s snow and wind.

Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Aspect/Elevation
  • 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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

Another round of stormy weather last night brought around 12″ snow to Girdwood and 6-8″ to the rest of the forecast area and surrounding zones. The rain level made it up to around 600-800′ last night, and the storm was accompanied by intense easterly winds with the Sunburst ridgetop station recording 8 hours of sustained winds around 40-60 mph and gusts as high as 105 mph last night. For today, our main concern will be avalanches failing within the new snow. Following last night’s winds, there is potential to see some very big human-triggered avalanches today even though the weather should be fairly quiet during the day.

Travel cautiously if you head into the mountains today. With temperatures warming through this storm, we’ve seen yet another upside-down storm with warmer, dense snow sitting on top of cold fluffy snow. This is a setup that can make new snow avalanches more reactive. This includes wind slab avalanches as well as storm slabs failing in steep terrain that was sheltered from the winds. Approach steep terrain with skepticism today, especially in areas that were on the high end of the storm totals from last night, or on slopes where last night’s winds formed a fresh round of reactive wind slabs. With speeds that strong, be on the lookout for slabs forming further downslope from ridgelines than ‘normal’.

With 15.8” Snow Water Equivalent, we are currently tracking well above previous El Niño seasons at Turnagain Pass and at 148% of median SWE for Dec 17 over the past 30 years. Data: NRCS, 12.17.2023

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

Aspect/Elevation of the Avalanche Problem
Specialists develop a graphic representation of the potential distribution of a particular avalanche problem across the topography. This aspect/elevation rose is used to indicate where the particular avalanche problem is thought to exist on all elevation aspects. Areas where the avalanche problem is thought to exist are colored grey, and it is less likely to be encountered in areas colored white.

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

This latest round of snow and wind is adding stress to the weak layer of faceted snow buried near the crust that formed during the Thanksgiving storm, now buried around 3-5′ deep. This is the third major loading event over the past week. We’ve been tracking this layer for the past few weeks, and we know it exists across the forecast zone. For now the layer has been on the unreactive side of stubborn, with only two known avalanches failing on this layer since the crust was buried three weeks ago.

Avalanche problems associated with crusts like this are notoriously difficult to predict, and we don’t want anyone to be caught off guard. The likelihood of triggering an avalanche on this layer is low, but if you were to trigger something it could be very large. With high uncertainty and severe consequences, we are being just a little more conservative than we would be if we were only dealing with the types of new snow avalanches mentioned in Problem 1 above. All slopes above 1000′ should be considered suspect, since we’ve seen the same suspicious structure in virtually every snowpit that has been dug over the past two weeks on all aspects across the advisory area.

This structure on Raggedtop is similar to what we’ve seen across the advisory area. Photo shared anonymously, 12.15.2023.

Weather
Sun, December 17th, 2023

Yesterday: Skies were cloudy with increasing winds through the day, and stormy weather picking up in the afternoon and overnight. Easterly winds were blowing 30-60 mph with gusts as high as 105 mph last night, and have backed down to around 10 mph out of the west this morning. A quick moving storm favored Girdwood with 12-14” snow, bringing 6-8” for the rest of our forecast area. The rain level moved up and down while during the storm, making it as high as around 600-1000 feet for some periods.

Today: Last night’s active weather is calming down this morning, and it is looking like things should remain quiet for the next few days. Skies should be partly to mostly cloudy today with winds out of the south and west at around 10-15 mph. High temperatures will be in the high teens to mid 20’s F with lows in the low to mid teens F. We may see a trace to an inch of snow today and tonight.

Tomorrow: Mild weather continues tomorrow, with partly cloudy skies and light westerly winds at 5-10 mph. High temperatures should be in the high teens to mid 20’s F with lows in the single digits to mid teens F. We may see a trace to 2” of snow, with snow to sea level.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 26 8 0.8 77
Summit Lake (1400′) 24 8 0.6 67
Alyeska Mid (1700′) 27 10 1.3 71
Bear Valley – Portage (132′) 29 1.04
Grouse Ck – Seward (700′) 27 3 0.4 38

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 20 ENE 30 105
Seattle Ridge (2400′) 24 ESE 13 37
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.