Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, December 29th, 2022 - 7:00AM
Expires
Fri, December 30th, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. Strong winds overnight combined with dry snow on the surface will form fresh wind slabs up to 2′ deep that are likely to produce human triggered avalanches. It is also possible for buried weak layers from 1.5 – 3′ deep to create large avalanches. From 1000′ to 2500′ the avalanche danger is MODERATE. Wind slabs are possible at the upper end of this elevation band. Below 1000′ the avalanche danger is LOW.

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Thu, December 29th, 2022
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Low (1)
Avalanche risk
Alpine
Above 2,500'
Avalanche risk
Considerable (3)
Treeline
1,000'-2,500'
Avalanche risk
Moderate (2)
Below Treeline
Below 1,000'
Avalanche risk
Low (1)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Recent Avalanches

Turnagain Pass:

Several large natural avalanches released sometime during or after the storm on Sunday/Monday. Yesterday we observed 4 large avalanches along the E and SE aspects of Seattle Ridge. The furthest north was approximately across from the Sunburst parking lot and the other three were in gully features on the SE aspect of Peak 4940′.  At 2200′ on the NW aspect of Magnum we saw another recent avalanche but it was hard to tell if it started at higher elevation. All these avalanches were roughly size D2 to D2.5 and likely released at the interface with the old snow surface or on a deeper weak layer.

Natural avalanche at 3200′ on SE aspect of Seattle Ridge that ran down into treeline elevations. You can see some brown color in the bed surface of this avalanche which could indicate it released on a deeper weak layer but it is hard to tell from afar. Photo 12.28.22

One of the avalanches off Peak 4940′ that released at about 3000′. This area is heavily wind loaded and it is difficult to see the exact extent of the crown, but the debris runs down into the small evergreens in the gully. Two more very similar avalanches were just N of this one along the SE face of Peak 4940′. Photo 12.28.22

Natural avalanche at 2200′ on NW face of Magnum. Due to the visibility it is hard to tell if this avalanche released up high and ran into lower elevations or just released on the steep lower roll on the NW ridge of Magnum. Photo 12.28.22

Avalanche Problem 1
  • Wind Slabs
    Wind Slabs
  • Aspect/Elevation
  • Almost 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.

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

Winds have picked up overnight coming out of the E and SE with averages of 15-25 mph and gusts to 45 mph at upper elevations. Above 2000′ there is 6″ or more of dry new snow on the surface which could easily be transported into fresh wind slabs up to 2′ deep. At higher elevations the new snow should be lighter and colder and will be easier for the wind to transport. To identify wind loaded features keep an eye out for shooting cracks, hollow feeling snow, and active wind loading. It is important to get off the beaten path to feel the snow surface around you and get a sense for areas that are more wind affected. Small test slopes can be a great way to determine if wind slabs are a concern in the area you are travelling. Wind slabs are most likely to be found along upper elevation ridgelines and cross loaded gullies.

At Turnagain Pass yesterday we found a breakable melt freeze crust 1-2″ thick up to about 2000′. There should be another couple inches of fresh snow on top of that now, but it definitely made for challenging travel at lower elevations. Above 2000′ the crust became very thick (6″) and supportable with about 6″ of new snow on top. Travel conditions were much improved once that melt freeze layer became supportable!

Below 1000′ the snowpack looked pretty saturated and wet loose avalanches are possible on steeper terrain features.

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

With the addition of 2″ of water since last weekend the structure of our snowpack is looking quite different. This is especially true at elevations below 3000′ where some of the recent precipitation fell as rain or wet snow. As the wet snow and melt freeze layers continue to freeze, the upper snowpack will become very strong and initiating an avalanche on a deeper buried weak layer will become much more difficult.

Above 3000′ we still have limited recent information about avalanche activity and how weak layers are reacting after the new snow load. Our stability tests yesterday indicated that the interface with the old snow surface which was about 1.5′ deep is the most concerning weak layer. We were not able to get any results on the layer of facets above the Thanksgiving melt freeze crust (3′ deep), but it may be possible to get a failure on this deeply buried weak layer at upper elevations or in parts of the forecast area with a thinner overall snowpack. Those typically thinner areas include Crow Creek in Girdwood and the southern end of Turnagain Pass near the Johnson Pass trail head.

We recommend a conservative approach to terrain selection and decision-making until we learn more about how the buried weak layers are reacting to the recent storm, especially at upper elevations where we have no information.

Snowpack structure at 2200′ on Tincan on a N aspect. The stand out features are the super thick melt freeze crust buried about 6″ deep and the interface with the old snow surface about 1.5′ deep. Photo 12.28.22

Weather
Thu, December 29th, 2022

Yesterday: Light rain from sea level to about 1000′. Girdwood and Turnagain Pass received 0.15 – 0.2″ of water while Portage recorded 0.9″ of water over the past 24 hours. Winds SE at 5-15 mph with gusts to 35 mph during the day, then increased to 15-25 mph in the alpine overnight with gusts to 45 mph. Cloud cover was mostly obscured during the day with occasional breaks in the clouds.

Today: Periods of light snowfall are possible today, especially in areas closer to the coast which could get up to 2″ of new snow. Snow line will be between sea level to 500′ today. Winds will remain moderate out of the SE with averages of 15-25 mph at upper elevations and gusts to 45 mph. Cloud cover should remain through the day but we may see some periods of higher cloud levels or broken clouds. Temperatures should remain in the twenties to low thirties today and drop slightly overnight to the low twenties.

Tomorrow: Continued periods of light snowfall and cloudy conditions are expected to persist. Areas near the coast could see a few inches of additional snowfall. Wind speeds are expected to decrease to E at 5-15 mph on Friday and temperatures should remain steady in the low to mid twenties.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 31 2 0.2 42
Summit Lake (1400′) 31 1 0.1 28
Alyeska Mid (1700′) 31 2 0.15 35
Bear Valley – Portage (132′) 37 0 0.9

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 23 ENE 17 44
Seattle Ridge (2400′) 26 SE 4 12
Observations
Recent Observations for Turnagain Pass
Date Region Location
02/08/23 Turnagain Observation: Eddie’s
02/07/23 Turnagain Observation: Seattle Ridge
02/07/23 Turnagain Avalanche: Pete’s North
02/06/23 Other Regions Observation: Johnson Pass to Bench Lake
02/05/23 Turnagain Observation: Rookie Hill
01/31/23 Turnagain Observation: Johnson Pass area
01/29/23 Turnagain Observation: Tincan Backdoor
01/28/23 Turnagain Observation: Sunburst
01/28/23 Turnagain Avalanche: Seattle Ridge
01/28/23 Turnagain Observation: Tincan Common
Riding Areas
Updated Fri, January 06th, 2023

Status of riding areas across the Chugach NF is managed by the Glacier and Seward Ranger Districts, not avalanche center staff. Riding area information is posted as a public service to our users and updated based on snow depth and snow density to prevent resource damage at trailhead locations. Riding area questions contact: mailroom_r10_chugach@fs.fed.us

Area Status Weather & Riding Conditions
Glacier District
Johnson Pass
Open
Opened Dec 13th.
Placer River
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Skookum Drainage
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Turnagain Pass
Open
Opened Dec 13th.
Twentymile
Closed
Closed Jan 5th due to lack of snow (holiday storms rained away the snow at sea level).
Seward District
Carter Lake
Open
Opened Dec 13th.
Lost Lake Trail
Open
Opened Dec 13th.
Primrose Trail
Open
Opened Dec 13th.
Resurrection Pass Trail
Closed
Closed to motorized use for the 2022/23 winter season per Forest Plan. Open next season.
Snug Harbor
Open
Opened Dec 13th.
South Fork Snow River Corridor
Open
Opened Dec 13th.
Summit Lake
Open
Opened Dec 13th.

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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.