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Archives
ARCHIVED - Forecasts expire after 24 hours.
Issued
Mon, December 19th, 2022 - 7:00AM
Expires
Tue, December 20th, 2022 - 7:00AM
Forecaster
Andrew Schauer
Avalanche risk The Bottom Line

The avalanche danger is MODERATE at all elevations. There is a weak layer of snow buried 2-4′ deep that makes it possible for a person to trigger a large avalanche. Persistent problems like this are difficult to assess, and the only way to avoid the problem is to stay on low-angle terrain.

PLACER/LYNX/JOHNSON PASS: We have very limited info for these recently opened motorized areas, and we suspect the weak snowpack is more problematic in the Lynx/Johnson Pass area. Use a little extra caution if you are getting out in these zones, and drop us a quick observation if you can.

Special Announcements

Chugach State Park: We continue to receive observations of concerning conditions in the Front Range. You can view those observations HERE. This includes recent avalanches, cracking/collapsing, and poor test results- all clear indicators that the avalanche conditions are dangerous.

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Mon, December 19th, 2022
Alpine
Above 2,500'
2 - Moderate
Avalanche risk
Treeline
1,000'-2,500'
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.
Recent Avalanches

The last known significant avalanches occurred during and just after last week’s storm. This includes multiple avalanches that failed on weak layers buried deeper in the snowpack in Girdwood, the south end of Seattle Ridge, Lipp’s, and Pete’s North.

A relatively smaller avalanche failing in the new snow from last week triggered this deeper pocket on the north side of Lipps. This is on the smaller side of the avalanches that we saw fail on the deeper weak layers- some of which were 500′ wide or more. 12.18.2022

Avalanche Problem 1
  • Persistent Slabs
    Persistent Slabs
  • Aspect/Elevation
  • 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.

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 main concern for today is triggering an avalanche on weak, faceted snow associated with a crust that formed just before Thanksgiving, now buried around 2-4′ deep. Persistent weak layers like this are difficult to predict, and are common culprits in avalanche accidents. As we get farther out from our last significant loading event (now 4 days ago), the layer is becoming more stubborn, and we are seeing fewer warning signs of unstable snow. This doesn’t mean the problem is gone. We had multiple poor test results yesterday on Cornbiscuit (details), not far from where multiple other groups observed large collapses and shooting cracks over the weekend (details here and here). These are clear signs that the snowpack is still capable of avalanching. On the other hand, there are tracks all over steep terrain around Turnagain Pass, so we know that the likelihood of triggering an avalanche is decreasing overall. We suspect the most dangerous conditions are in the mountains closer to Girdwood, as well as on the south end of the pass. Both of these zones saw the most avalanche activity following the last storm.

The only way to manage a problem like this is by careful terrain management. Give yourself wide margins for error by avoiding steep, consequential terrain. This includes big, connected terrain features and steeper slopes above terrain traps like gullies, rocks, or trees. Ask yourself, what would happen if this slope were to avalanche? Persistent slab avalanches have a nasty tendency to release after there are multiple sets of tracks on a slope, or after a person gets way out into the middle of a slab.

Dry Loose Avalanches: With several days of clear, cold, and calm weather, there is plenty of soft snow on the surface. This will make dry loose avalanches (sluffs) likely in steep terrain. While these are unlikely to become big enough to bury a person, they can be dangerous if they carry you into terrain traps.

The poor structure in this snowpit is fairly consistent across the advisory area. Those test results highlighted in red suggest the snowpack is still capable of producing an avalanche. That is the layer we are concerned about. Photo: Andy Moderow. 12.18.2022

Click here to view the video below if it doesn’t load in your browser.

Weather
Mon, December 19th, 2022

Yesterday: We had another day of clear, calm, and cold weather with temperatures struggling to get above 0 F in the valleys, but an inversion brought temperatures into the low teens F at higher elevations. Winds were light and variable, with no precipitation.

Today: Today is looking like another day of quiet weather, with high temperatures making it into the mid teens F and overnight lows getting back down into the single digits F. Winds should be light out of the east, with no precipitation during the day. We are expecting scattered clous, and there is a chance we might see some flurries tonight, but it shouldn’t be any significant precip.

Tomorrow: Cloud cover will build tonight into tomorrow, with light flurries possible and high temperatures in the low to mid teens F. Winds should be light out of the east to northeast. The next round of snow is looking to arrive Wednesday evening, with around 3-6″ overnight into Thursday.

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

Temp Avg (F) Snow (in) Water (in) Snow Depth (in)
Center Ridge (1880′) 15 0 0 39
Summit Lake (1400′) -3 0 0 28
Alyeska Mid (1700′) 13 0 0 42
Bear Valley- Portage (132′) -4 0 0

RIDGETOP 24-hour data (6am – 6am)

Temp Avg (F) Wind Dir Wind Avg (mph) Wind Gust (mph)
Sunburst (3812′) 9 W-E* 5 20
Seattle Ridge (2400′) 13 W-E 3 10

*Winds shifted directions around 6:00 p.m.  yesterday.

Observations
Recent Observations for Turnagain Pass
Date Region Location
02/29/24 Turnagain Observation: Silvertip Creek
02/27/24 Turnagain Observation: Seattle Ridge
02/25/24 Turnagain Observation: Kickstep NE Bowl
02/24/24 Turnagain Observation: TinCan Backdoor/ Center Ridge
02/22/24 Turnagain Avalanche: Lynx Creek
02/22/24 Turnagain Observation: Turnagain, Seattle, Mt Ascension
02/21/24 Turnagain Observation: Tincan Trees
02/21/24 Turnagain Observation: Sunburst
02/20/24 Turnagain Avalanche: Tincan
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.