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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, March 27th, 2023 - 7:00AM
Expires
Tue, March 28th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is CONSIDERABLE at all elevations. We have seen multiple very large human-triggered avalanches over the past two days, and similar activity is possible today. These avalanches have been triggered remotely from low-angle terrain connected to steeper slopes, and avalanches have been running far into valley bottoms. Dangerous avalanche conditions exist right now, and the only way to manage the problem is to avoid traveling on or below steep terrain.

SUMMIT LAKE / SEWARD / LOST LAKE / SNUG HARBOR:  Dangerous avalanche conditions are suspected in these areas as well.

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Mon, March 27th, 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
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

We received word of a large remote-triggered avalanche yesterday in Palmer Creek near Hope (details here). The avalanche was triggered from flat terrain below the slope, and ran across the bottom of the valley. It carried multiple snowmachines, partially burying one. No people were caught or carried. This is the fourth very large remote-triggered avalanche in the area over the weekend, including two on the back side of Seattle Ridge, and one in the Skookum Valley.

This very large avalanche was triggered remotely from the flat terrain below the slope that released. This is the fourth remote-triggered avalanche that we know of in the past two days. Photo: Seth Kiester. 03.26.2023

Avalanche Problem 1
  • Deep Persistent Slabs
    Deep Persistent Slabs
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
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.

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

The snowpack showed us what it is capable of this weekend. We have seen four very large remotely-triggered avalanches in the past two days, and the problematic setup that is making this possible is going to take a long time to go away. These avalanches have been triggered from low-angle terrain connected to steeper slopes, and in some cases people were standing up to a half mile away when they triggered the avalanche. In some cases, people have triggered releases on multiple slopes and multiple aspects at the same time (see more info on avalanches on Seattle Ridge here and here). All of these avalanches have run far into valley bottoms (See more here from the massive avalanche in the Skookum Valley Saturday), and we are really lucky that nobody has gotten caught in any of them.

Sometimes these deep slab avalanches are hard to predict, with weak layers lurking under the surface and a high amount of uncertainty as to whether a person can actually trigger a large avalanche. This is not one of those ‘hard-to-predict’ times. All of the recent avalanche activity shows us that we are dealing with a very dangerous snowpack, and it is nothing to mess with. We’ve seen activity on both sides of the highway at Turnagain Pass, multiple large avalanches in the Placer/Skookum area, and more large avalanches around the periphery of our advisory area in Summit and Palmer Creek. For now the only way to manage the problem is to avoid traveling on or below steep avalanche terrain.

If our video from the crown of the large natural avalanche on the north side of Sunburst does not load, you can view it here.

Avalanche Problem 2
  • Wet Loose
    Wet Loose
  • Aspect/Elevation
  • Certain
    Very Likely
    Likely
    Possible
    Unlikely
    Likelihood
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
    Size
Wet Loose
Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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

We are looking at another day of warm temps and partly sunny skies. It will be a race between the warming daytime temperatures and increasing cloud cover that will determine whether we see loose wet avalanche activity this afternoon. If the clouds build early enough, it is likely the snow will stay dry even on solar aspects as it did yesterday. If things do end up heating up enough this afternoon, or if there is enough sun shining later in the day, we expect to see loose snow avalanches this afternoon. These will likely be preceded by rollerballs releasing, and it should be noticeable that the snow surface is becoming moist as things start to heat up. If things do get warm enough, there is a chance that loose snow avalanches failing near the surface may trigger something bigger deeper in the snowpack (see problem 1 for more on that). Pay attention to changing conditions while you are out today, and be ready to move to shaded slopes if you notice things heating up this afternoon.

Weather
Mon, March 27th, 2023

Yesterday: The day started off mostly sunny, but high clouds building through the day were enough to keep snow surfaces dry. Temperatures climbed from the single digits to low teens F in the morning up to the mid to upper 30’s F in the afternoon. Winds were calm, with light gusts from variable direction. No precipitation was recorded.

Today: Things are looking very similar today, with high clouds likely and building through the day. Temperatures are currently in the upper teens to low 20’s F, but should reach the upper 20’s to mid 30’s F during the day before dropping back down to the upper teens to low 20’s F tonight. Winds will be light and variable, and there is a chance for some snowflakes tonight but no accumulation is expected.

Tomorrow: A low pressure system to the west of us will increase cloud cover and chances for precipitation tonight, but it is looking like we will only get a trace of new snow. Skies should be partly to mostly cloudy during the day tomorrow with some flurries possible. Winds should be light out of the west. High temperatures will be in the upper 20’s to low 30’s F, with overnight lows dropping back into the mid teens to low 20’s F.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 25 0 0 101
Summit Lake (1400′) 21 0 0 50
Alyeska Mid (1700′) 27 0 0 93
Bear Valley – Portage (132′) 24 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 25 W-E* 3 14
Seattle Ridge (2400′) 23 ESE 4 9

*Wind direction changed around 4 p.m. yesterday.

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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.