Turnagain Pass Avalanche Forecast RSS

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ARCHIVED FORECAST - All forecasts expire after 24 hours from the posting date/time.
Issued
Thu, March 3rd, 2022 - 7:00AM
Expires
Fri, March 4th, 2022 - 7:00AM
Forecaster
John Sykes
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE above 2500′. Strong winds and new snow over the past 12 hours have created fresh wind slabs up to 2′ deep that are likely for human triggering and possible for natural avalanches. This storm buried a layer of surface hoar that existed on all aspects and elevations and could cause wind slabs to be larger than normal and possibly release on lower angle slopes if the surface hoar was buried intact. Below 2500′ the avalanche danger is MODERATE, where lighter winds will make natural avalanches unlikely and wind slabs will be shallower.

PORTAGE/PLACER: The Portage and Placer zones could see up to a foot of new snow by the end of the day today and elevated avalanche danger exists at all elevations. This will cause wind slabs to be up to 3′ deep and create the potential for natural and human triggered storm slabs in the new snow in areas protected from the wind.

SUMMIT LAKE: Strong winds over the past 12 hours have created fresh wind slabs at upper elevations that have the potential to release naturally and trigger deeper avalanches on buried weak layers. Careful evaluation of the snowpack and conservative decision-making is recommended.

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Thu, March 3rd, 2022
Alpine
Above 2,500'
Considerable (3)
Avalanche risk
Treeline
1,000'-2,500'
Moderate (2)
Avalanche risk
Below Treeline
Below 1,000'
Moderate (2)
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
Moderate (2)
Danger Scale:
No Rating (0)
Low (1)
Moderate (2)
Considerable (3)
High (4)
Extreme (5)
Avalanche Problem 1
  • Storm Slabs
    Storm Slabs
  • Almost Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic
    Very Large
    Large
    Small
    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 quick pulse of wind and snowfall over the past 12 hours has added some much needed new snow on top of the mostly crusty and wind hardened surfaces in the forecast area. Turnagain Pass and Girdwood received 3-5″ of new snow overnight with Portage and Placer getting closer to 6-8″ of new snow. An additional 1-3″ is forecast today for Turnagain and Girdwood with 5-7″ of additional snow in Portage and Placer. Accompanying this new snowfall are strong winds at ridgetops, averaging 20-35 mph with gusts into the 60s over the past 12 hours. In the core forecast area the snowpack is generally stable and surface avalanche problems associated with the new snow and wind will be the main concern (see additional concerns for discussion of weaker snowpack in periphery areas).

This storm will have created fresh wind slabs up to 2′ deep at upper elevations that are likely for a person to trigger today and possible for natural avalanches. A layer of surface hoar was observed up to ridgetop elevations early this week which could cause wind slabs to propagate more widely than usual if the surface hoar is still intact. Stopping to check whether this layer of surface hoar is upright or was knocked over by winds in the area you are travelling today should give you a better sense of whether the wind slabs will have normal character or perhaps more of a persistent weak layer character with wider propagation and the potential for triggering avalanches on lower angle slopes. Wind slabs are most likely to be found on upper elevation ridgelines, cross loaded gullies, and under convex rolls.

In protected areas storm slabs are possible, especially where the surface hoar was buried intact and was deposited on a firm surface. In Turnagain Pass and Girdwood storm slab avalanches will be less likely today because of limited new snow on top of the buried surface hoar. However, in Portage and Placer total storm snow could be close to a foot by the end of the day today which will make triggering larger storm slabs more likely.

Surface hoar over a thin crust on Seattle Ridge from 3.1.22

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

In shallow snowpack areas of the forecast zone, like Crow Pass in the far north and Lynx Creek in the far south, we are still concerned about a layer of facets from November that are in between the New Years crust and Halloween crust. The potential for human triggered avalanches on this layer is pretty low because of multiple strong crust layers in the upper snowpack, but if an avalanche was initiated on this layer it has the potential to propagate widely and create a very large avalanche. This layer of facets is more of a concern in the Summit Lake area, which is outside the forecast zone, where an overall shallower snowpack exists and the upper snowpack is much weaker.

Glide Avalanches: A few glide cracks have opened back up on Seattle Ridge above the motorized up track. These are highly unpredictable and can produce very large and destructive avalanches, so we recommend minimizing your time spent underneath them.

Snowpack structure in Summit Lake area showing November facets sandwiched between the New Years and Halloween crusts (see ob here). Photo Aleph Johnston-Bloom 2.27.22

Weather
Thu, March 3rd, 2022

Yesterday: Winds started to pick up in the afternoon with averages in the 20-35 mph range and gusts up to 50-60 mph overnight. Snowfall started in the evening with 0.3″ of water falling overnight in Girdwood and Turnagain Pass which should be about 3-5″ of snow. Portage and Placer have seen 0.6″ of water over the past 12 hours which fell as snow down to sea level and should amount to about 6-8″ of snowfall.

Today: Peak precipitation rates and winds should be in the early morning with snowfall tapering off throughout the morning and ending in the afternoon. Winds will also taper off throughout the day and switch to a more southerly flow this afternoon. Winds will be in the 10-30 mph range with gusts up to 50-60 mph during the tail end of the storm. Another 1-3″ of snow accumulation is possible today in Turnagain and Girdwood with up to 6″ of snow possible in Portage and Placer. Snow level could rise up to 100′ today but most of the snowfall should be over by the time the temperatures increase.

Tomorrow: Unsettled weather is expected to persist Friday, with snowfall continuing in coastal areas. Another low pressure system is going to impact the area overnight on Friday into Saturday morning bringing additional snowfall and increased winds.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 30 4 0.2 94
Summit Lake (1400′) 25 0 0.3 40
Alyeska Mid (1700′) 29 3 0.2 NA

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 18 ENE 22 62
Seattle Ridge (2400′) 22 SE 12 27
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Riding Areas
Updated Fri, May 13th, 2022

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
Closed
Closed as of May 1 per Forest Plan.
Placer River
Closed
Closed as of April 25th due to insufficient snow coverage.
Skookum Drainage
Closed
Closed as of April 1st per Forest Plan.
Turnagain Pass
Open
Open. Extended opening through May 31.
Twentymile
Closed
Closed as of April 6th due to insufficient snow coverage.
Seward District
Carter Lake
Closed
Closed as of May 1 per Forest Plan.
Lost Lake Trail
Closed
Closed as of May 1 per Forest Plan.
Primrose Trail
Closed
Closed as of May 1 per Forest Plan.
Resurrection Pass Trail
Closed
Closed as of May 1 per Forest Plan.
Snug Harbor
Closed
Closed as of May 1 per Forest Plan.
South Fork Snow River Corridor
Closed
Closed as of May 1 per Forest Plan.
Summit Lake
Closed
Closed as of May 1 per Forest Plan.

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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.