Mon, January 23, 2023 Turnagain Pass Avalanche Forecast

Mon, January 23rd, 2023

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

0 - No Rating

1 - Low

2 - Moderate

3 - Considerable

4 - High

5 - Extreme


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

Tincan South Side: We remotely triggered an avalanche near the Snake Pit on the south side of Tincan yesterday. We were digging pits on a low-angle bench when the avalanche released about 50′ below us where the slope rolled over into steeper terrain. The avalanche was about 2′ deep and 75′ wide, running only 150′ before piling debris up on a flat bench. Nobody was on or below the slope that failed. More details here.

Lynx Creek: We received details yesterday of a snowmachine-triggered avalanche in the Lynx Creek drainage on Saturday. The rider noticed the slope cracking around him and was able to ride off the slab without getting buried. The avalanche was 300′ wide and 2′ deep, likely failing on the 1/10 buried surface hoar layer that has been so reactive for the past week. It is worth mentioning that the group had put multiple sets of tracks on the same slope before the last rider triggered the avalanche. Thanks to the rider for sharing the information from the avalanche. There are more details in this observation.

Photo from the crown of the avalanche we triggered on Tincan yesterday.

Avalanche Problem 1

Persistent Slabs
N E S W NW NE SE SW

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

This layer of buried surface hoar is proving to be quite the persistent problem. There have been natural and human-triggered avalanches on this layer for 8 days in a row now, and it will remain reactive today. With another 0.5-.75″ snow water equivalent (SWE) and strong winds in the past 24 hours, the snowpack continues to see more stress added to this weak layer. Although winds and precipitation are expected to back off for most of the day today, dangerous conditions continue to exist.

As the layer gets buried deeper, it is slowly becoming more stubborn to trigger. However, with this impressive string of human-triggered avalanches, there is no question that it is still reactive throughout our advisory area. Over the past week we’ve seen activity in almost every part of Turnagain Pass– including Seattle Ridge, Eddie’s, Tincan, Sunburst, Magnum, Cornbiscuit, Pete’s North, and Lynx Creek. Now that the layer is around 2′ deep or deeper, it is becoming harder to detect with common travel tests like hand pits. It is also giving fewer warning signs like shooting cracks or collapsing. Case in point- I was unable to find the layer with hand pits along the skin track yesterday in the Tincan trees, and had been stomping around on the top of a convex roll without any results just minutes before we triggered a large avalanche remotely on the same terrain feature.

The snowpack continues to show its potential for making avalanches, and with continued snow and wind the avalanches are only getting bigger. The only way to manage a dangerous setup like this is by avoiding traveling on or below steep terrain.

Wind Slabs: Winds are backing off slightly this morning, but will be picking up again this afternoon. Pay attention to active wind loading later in the day, and be aware of an increased likelihood of natural and human-triggered avalanches on wind loaded slopes as the wind returns.

The1/10 buried surface hoar was still reactive in this pit (ECTP 25). The test result was less important than the fact that we triggered a big avalanche just below the pit. 01.22.2023

Avalanche Problem 2

Deep Persistent Slabs
N E S W NW NE SE SW

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

Likelihood of Avalanches

Size of Avalanches

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

In addition to the buried surface hoar layer mentioned above, we are also still concerned with the Thanksgiving crust/facet layer– now buried 4-8′ deep on average. At this point, the layer is so deep that a person would need to find just the right (wrong?) spot to trigger it. Deep slab problems are tricky, since they are so stubborn but if you do find a thin spot where the weight of a person can collapse the weak layer, the avalanche could take down the entire mountainside. Stability tests tell us very little about the layer, and it will almost never give warning signs like shooting cracks or collapsing. They are also notorious for releasing after there are multiple sets of tracks on the slope.

As time goes on it is becoming less likely that a person will trigger an avalanche on this layer, but it is still on our radar for now. Given the widespread persistent slab problem mentioned in problem 1 above, this monster is just one more reason to avoid traveling on or below steep terrain for now.

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Weather

Mon, January 23rd, 2023

Yesterday: Sustained snow showers brought 4-8″ new snow equaling 0.4-0.75″ snow water equivalent (SWE). Easterly winds were blowing 20-35 mph with gusts of 45-55 mph, backing down to 5-15 mph this morning. High temperatures were in the mid 20’s at upper elevations and mid 30’s at lower elevations. The rain line reached around 800-1000′.

Today: Winds are backing off this morning, currently blowing 5-15 mph out of the southeast. They are expected to pick up to 15-20 mph and shift more southerly later today through tonight. Most of today’s precipitation will miss the advisory area, with only a trace to 2″ of snow above 1500′ equaling up to 0.15″ SWE. Skies will be cloudy with high temperatures in the upper 20’s to low 30’s F and slightly increasing through the day into tonight.

Tomorrow: Stronger southeasterly winds will continue for most of the day tomorrow, with sustained speeds around 15-25 mph and gusts of 20-35 mph. We should see light precipitation during the day bringing another trace to 2″ snow. Precipitation should pick up a bit tomorrow night, with 3-5″ snow possible at higher elevations, but the rain line is going to start moving up to close to 2000′. Skies should be mostly cloudy with temperatures hovering in the upper 20’s at higher elevations and mid 30’s at lower elevations.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	31	4	0.4	71
Summit Lake (1400′)	31	2	0.2	34
Alyeska Mid (1700′)	31	5	0.4	70
Bear Valley – Portage (132′)	37	rain	0.8	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	19	54
Seattle Ridge (2400′)	26	SE	10	29

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
04/23/24	Turnagain	Observation: Turnagain Sunny Side	Travis SMITH
04/21/24	Turnagain	Observation: Bertha Creek	Anonymous
04/20/24	Turnagain	Avalanche: Spokane Creek	Schauer/ Mailly Forecaster
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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