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ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, March 6th, 2023 - 7:00AM
Expires
Tue, March 7th, 2023 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE above 1000′ today. Warm temperatures and mostly sunny skies will make loose avalanches the main concern, and there is a smaller possibility that these loose snow avalanches could pull out bigger slabs on isolated slopes. It is difficult to predict how the snowpack will respond to the first  major warming event of the season, so it will be important to pay attention to warning signs and dial back your terrain if you see conditions changing in the heat of the afternoon. The danger will remain LOW below 1000′.

Special Announcements

Turnagain Pass Avalanche Awareness Day – 2023:  Mark your calendars for Saturday, March 18th, and swing by on your way to or from your backcountry ride or ski!! Test your beacon skills, chow down on hot dogs, and bring your questions. The Alaska Avalanche School will be there along with a chance to demo snowmachines from Alaska Mining and Diving Supply and Anchorage Yamaha and Polaris. More details HERE!

Mon, March 6th, 2023
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.
Recent Avalanches

There were two small human-triggered avalanches reported yesterday. One was a skier-triggered slab in the Goldpan area up above Magnum and Cornbiscuit. The avalanche was small and the skier was not caught. The other was a very small snowmachine-triggered slab in Lynx creek, which either occurred Saturday or Sunday.

A group skiing in Pete’s North yesterday observed a large collapse just above treeline. This didn’t lead to an avalanche, but it is the third observation in two weeks noting concerning structure that seems to be confined to Pete’s. We don’t usually forecast for such a specific piece of terrain, but it seems like there is cause for concern in that area right now that doesn’t exist for most of the rest of the advisory area.

Avalanche Problem 1
  • 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

Temperatures are on the rise again today, and uncertainty is high with just how the snowpack will respond. It is likely we will see some loose snow avalanches as things heat up later in the day. This should start out with rollerballs releasing near rocks and trees, which will likely start to entrain loose snow at the surface as the snowpack warms. This type of activity was observed yesterday, and we should expect more of the same today. These loose snow avalanches should be on the smaller side, and can easily be managed by avoiding steep southerly terrain later in the day. The first sign of deteriorating conditions will be those rollerballs- small chunks of snow rolling down steep terrain. If you notice that kind of activity, it is time to move to shaded terrain.

The bigger question will be how the snowpack responds just below the surface. There is a chance that a loose snow avalanche near the surface could pull out a bigger slab. This may be a stubborn wind slab that formed towards the end of last week, or even one of those weak layers in the upper 2-3′ of the snowpack that have been mostly unreactive. Yesterday we noted two small human-triggered avalanches in steep alpine terrain, and similar activity will be possible again today. This is the beginning of the first major warming event of the season, and we need to be paying attention to changing conditions as things heat up later in the day.

Cornice Fall: Cornices are going to heat up just like the rest of the snowpack. This will make them more tender, making natural cornice falls possible and making it even easier for a person to cause one to break. A falling cornice can be dangerous enough on its own, but there is a good chance that a falling cornice will trigger a slab avalanche as it tumbles down the hill. People noticed a cornice-triggered avalanche that was a few days old near Captain’s Chair yesterday, and there was similar activity on Goat Mtn. above Girdwood as well.

Dry Loose Avalanches (Sluffs): It is likely people will trigger sluffs in steep terrain with soft, dry snow on the surface. It is unlikely these will be big enough to bury a person, but they can be dangerous in consequential terrain where a fall would carry you over rocks, cliffs, or through trees.

Glide Avalanches: We received reports of fresh glide activity in the Summit Lake area yesterday. As temperatures continue to climb over the next few days, we may see more glide cracks open up and we may even see some glide avalanches release. These are impossible to predict and are very large and dangerous. The good news is that they are easy to manage by simply avoiding spending any time below glide cracks.

Rollerballs in steep southerly terrain in the Spokane Creek drainage yesterday. This will be the first sign that stability is deteriorating, and it is time to seek out shaded slopes. Photo: Alaska Guide Collective. 03.05.2023

Debris from loose snow avalanches below just about every gulley in the Library yesterday. Similar activity is likely as warm temperatures continue today. Photo: Rachel Heath, 03.05.2023

Additional Concern
  • Persistent Slabs
    Persistent Slabs
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.
More info at Avalanche.org

As mentioned above, we are still keeping the weak layers of snow in the upper snowpack on our radar for now. For the most part, it seems these have become unreactive for most of our advisory area. The most concerning places where these weak layers may still be lingering are in the zones with a thinner snowpack. We’ve seen multiple observations pointing towards reactive weak layers towards the south end of Turnagain Pass and Summit Lake, and we suspect there may be similar structure towards Crow Pass. As the snowpack heats up today and tomorrow, it is worth keeping these layers in mind while you are choosing your terrain.

Weather
Mon, March 6th, 2023

Yesterday: Winds were light out of the north at 5-10 mph with gusts from around 10-15 mph. Skies were mostly sunny, with some high clouds moving in during the afternoon. The coldest temperatures in the past 24 hours were yesterday morning, with temps in the single digits F in the valleys and in the low teens F at higher elevations. High temperatures made it up into the mid 20’s F at lower elevations and up into the mid 30’s F near ridgelines. As of 5:00 this morning, temperatures are in the mid teens to low 20’s F in the valleys and in the upper 20’s to low 30’s F at higher elevations. We did not receive any precipitation yesterday.

Today: The temperature inversion continues to build today, with high temperatures expected to reach the mid to upper 30’s F, and the warmest temperatures around 3000’-5000’ elevation. Winds should be light out of the northwest around 5 mph with gusts around 10 mph. Skies will be partly cloudy with some upper level clouds, and no precipitation is expected today.

Tomorrow: The inversion continues to build tonight into tomorrow. It is likely we will see temperatures stay above freezing tonight, with daytime highs tomorrow possibly getting into the 40’s F between 3000’-5000’. Skies should be mostly sunny with light westerly winds. No precipitation is expected tonight or tomorrow.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 19 0 0 67
Summit Lake (1400′) 15 0 0 38
Alyeska Mid (1700′) 18 0 0 68
Bear Valley – Portage (132′) 12 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 31 W 8 18
Seattle Ridge (2400′) 27 NNE 2 7
Observations
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02/20/24 Turnagain Observation: Seward Highway across from Johnson Pass TH
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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.