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Wed, March 3rd, 2021 - 7:00AM
Thu, March 4th, 2021 - 7:00AM
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE today, and it is still possible to trigger an avalanche on persistent weak layers buried 1-3’ deep. Without a new load, these layers are becoming more stubborn but they are still capable of producing avalanches. Safe travel will require careful terrain evaluation and good group management, which means only exposing one person at a time to steep slopes and avoiding terrain where getting caught in an avalanche would have severe consequences.

Seward/Lost Lake/Portage Valley: These areas are expected to see more wind today, which will make it possible to trigger fresh wind slab avalanches forming during the day.

Wed, March 3rd, 2021
Above 2,500'
2 - Moderate
Avalanche risk
2 - Moderate
Avalanche risk
Below Treeline
Below 1,000'
2 - Moderate
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
  • Persistent Slabs
    Persistent Slabs
  • Certain
    Very Likely
  • Historic (D4-5)
    Very Large (D3)
    Large (D2)
    Small (D1)
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

Well, it looks like March hasn’t yet received Aleph’s letter from Monday…

With another day of clear, calm, and cool weather on the way, and two persistent weak layers in the upper snowpack, today’s avalanche conditions are going to look very similar to yesterday’s. Our main concern is triggering an avalanche on persistent weak layers that formed during late January and early February and are now buried 1-3’ deep. These layers are slowly gaining strength, which means it is becoming more difficult to trigger an avalanche, but it is still possible. We saw human-triggered avalanches failing on these layers at Tincan and near the Girdwood Valley over the weekend, and similar activity will be possible today.

Persistent weak layers require patience and good decision making. Since we have found them at most locations in our advisory area, it is not really reasonable to rule out any chunk of steep terrain as potentially dangerous. So how do you manage a problem like this? Stick with the status quo that we have been talking about for several weeks now– be careful with your route finding and smart with your group management. This means avoiding consequential terrain exposed to terrain traps, only exposing one person at a time to steep slopes, and watching your partners from safe spots.

Wind Slabs: You may still find small and isolated pockets of wind-loaded snow that are capable of avalanching. These are most commonly located below ridgetops, convexities, and in cross-loaded gullies, and will be more likely at higher elevations. Steep terrain with smooth pillows of wind-drifted snow should still be treated with caution today. As mentioned in the bottom line, gap winds today will be building fresh wind slabs around Seward, Lost Lake, Snug Harbor, and the Portage Valley.

Sluffs: Steep slopes that have been protected from the winds now have 2-6” of soft snow on the surface. With continued cool temperatures, this snow is still poorly bonded, which makes it easier to trigger dry loose avalanches (sluffs). Be aware of the potential for sluffs to gain volume and speed in steep terrain, since these can be dangerous if they take you for a ride.

A group of two working their way up Sunburst above the valley fog yesterday. 03.02.2021

Wed, March 3rd, 2021

Yesterday: High temperatures reached the mid teens to upper 20s F, with a few hours above 30 F recorded at the Seattle Ridge weather station. Skies were mostly sunny with some thin upper level clouds and a thick layer of valley fog up to around 2200’ that stayed in place until the early afternoon. Winds were light at around 5 mph gusting to 18 mph, with variable direction.

Today: Temperatures this morning are generally in the single digits to low teens F, with the coldest temperatures near Summit Lake at -1 F. Highs are expected in the mid teens to low 20s F, with slightly warmer temperatures near Seward. Northwesterly winds are expected to remain light at 5 mph, with stronger winds near Seward, Portage, and Whittier. Skies will be mostly sunny, with a layer of valley fog lasting until mid day.

Tomorrow: Active weather will start to ramp up late in the day or overnight tomorrow. Easterly winds will be light at around 5 mph for most of the day before picking up to 15 mph in the evening. Skies will be mostly sunny during the day, with clouds expected to move in with the increasing winds in the evening. No snowfall is expected during the day, but chances improve overnight and into Friday. It’s not looking big, but hopefully we will get something out of it.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 13 0 0 113
Summit Lake (1400′) 8 0 0 46
Alyeska Mid (1700′) 16 0 0 118

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 13 var. 5 18
Seattle Ridge (2400′) 16 NE 1 8
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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.