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ARCHIVED - Forecasts expire after 24 hours.
Issued
Fri, March 11th, 2022 - 7:00AM
Expires
Sat, March 12th, 2022 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′. Light snow and moderate winds over the past 48 hours have made it possible for a person to trigger an avalanche up to 1-2′ deep. The most likely places to trigger an avalanche will be near ridgelines, convex rolls, and steep gullies. There is also a layer of buried surface hoar in the upper 2′ of the snow pack that may be capable of producing avalanches in some parts of the advisory area today. The danger is LOW below 1000′, where the primary concern will be wet loose avalanches in steep terrain.

Special Announcements

The annual Turnagain Pass Avalanche Awareness Day is happening next Saturday, March 19th!! Stop by the Seattle Ridge parking lot to chat with CNFAIC forecasters, try out some avalanche rescue gear, and demo a snowmachine or two from local businesses such as AMDS and Anchorage Yamaha and Polaris. It’s always a fun event!

Fri, March 11th, 2022
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
1 - Low
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
  • Wind Slabs
    Wind Slabs
  • 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.
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

Moderate winds and steady snowfall over the past two days have built sensitive wind slabs that will remain reactive to human triggers today. With modest snow totals, these avalanches are likely to be around a foot deep, but some areas with heavier snow and stronger winds may see slabs form up to 2′ deep. Sensitive slabs will have formed on the usual suspect terrain features- steep slopes near ridgelines, convex rolls, and steep gullies. This avalanche problem will be larger and more widespread at higher elevations where winds have been stronger. This new snow load is adding a little more stress to a recently buried layer of surface hoar, which has the potential of making slightly larger avalanches today. More on that in problem 2 below.

Be on the lookout for signs of fresh wind loading and unstable snow today. A fresh wind slab will feel slightly stiffer than storm snow that has been sheltered from the wind. The dangerous combination of stiffer snow on softer snow may feel ‘punchy’. Keep an eye out for cracks shooting out from your skis or snowmachine as key information indicating unstable snow.

Looking down at a small skier-triggered wind slab off Tincan’s CFR. Photo: Andy Moderow. 03.10.2022

Avalanche Problem 2
  • Persistent Slabs
    Persistent Slabs
  • 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.
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

The layer of surface hoar that got buried last week is still on our minds today. This layer has been gaining strength, and hopefully will evolve into a non-issue. For now it is still possible for a person to trigger an avalanche on this layer in some parts of the advisory area. The layer seems most concerning in the Seattle Ridge zone, with several avalanches failing on the layer last week, and large surface hoar grains still reactive in test pits just before this most recent storm arrived (details in this observation from Monday). We’ve also seen the layer on the skier side of Turnagain Pass, but it has been several days since we have gotten any unstable results in test pits.

For today, it is important to keep this layer in mind before heading into avalanche terrain. As mentioned above, keep an eye out for the classic warning signs like shooting cracks and collapsing, as well as fresh avalanche activity. As always, take a minute to step off the skin track or hop off your machine and assess the snow before heading into avalanche terrain. In areas where this layer is problematic, it has been easily identified in quick hand pits, and has been propagating in stability tests. If you see any of these warning signs, or if you are less confident in your snowpack assessment, it is best to avoid steep terrain for now and give this layer a little more time to heal.

Surface hoar crystal from a snowpit in the Tincan Trees yesterday. 03.10.2022

Weather
Fri, March 11th, 2022

Yesterday: We saw continued mild temperatures under cloudy skies yesterday, with highs in the upper 20’s F at ridgetops and the mid to upper 30’s at mid and low elevations. 24-hour snow totals are around 1-3″ in Girdwood with a trace to 1″ at Turnagain Pass. Rain made it up to around 1100′. Winds were out of the east at 10-20 mph with gusts of 30-45 mph.

Today: Light snowfall may continue to trickle in today, with a trace to 2″ possible. Clouds are expected to break up a little bit, with some periods of sun possible throughout the day. Winds are expected around 5-15 mph out of the east, with gusts of 15-25 mph. It is looking like winds will die down throughout the day at Turnagain Pass, but they may actually increase slightly near Girdwood and Crow Pass. The rain line is expected to hover around 1000′

Tomorrow: Overnight lows are expected in the low 20’s to 30 F, with a trace of precipitation tonight. Skies will be mostly cloudy during the day, with some sun poking through the clouds at times. No precipitation is expected during the day. Winds should be light out of the east, around 5-10 mph, with high temperatures in the mid 20’s to low 30’s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 32 0 0 94
Summit Lake (1400′) 33 0 0.1 41
Alyeska Mid (1700′) 32 2 0.15 N/A

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 22 ENE 13 41
Seattle Ridge (2400′) 26 SE 11 23
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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.
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