Thu, February 02, 2023 Turnagain Pass Avalanche Forecast

Thu, February 2nd, 2023

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

1 - Low

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

The last human-triggered avalanches were 12 days ago, when multiple people were caught, carried, and some partially buried in avalanches failing on the layer of buried surface hoar we are still concerned with. You can find details from some of these avalanches here and here.

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

It’s Groundhog Day today, literally and figuratively. We’re looking at another cloudy day with cooler temps and light winds, and nothing has changed in the snowpack since yesterday. Without any big changes expected in the weather today, our primary concern is the lingering possibility of triggering a large avalanche on the layer of surface hoar buried 2-3′ deep across our advisory area. We know this layer is slowly gaining strength and becoming more stubborn to trigger, but it is not quite to the point where we can write it off as being unreactive. Part of the uncertainty we are dealing with right now comes from the fact that there just hasn’t been a whole lot of traffic at Turnagain Pass lately– which means observations on this layer have been sparse since the string of human-triggered avalanches almost two weeks ago.

For now, we are starting to feel comfortable pushing into some steeper terrain, but we are doing it very carefully. This means taking the time to assess the weak layer where we are traveling by digging down and testing it before getting on steeper slopes. Any red flags like shooting cracks or collapsing should be enough reason to back off steep terrain. Because of the uncertainty associated with this weak layer, we are starting really small with steep terrain. This means smaller features and shorter slopes without any terrain traps that increase the consequences of getting caught in an avalanche– things like gullies, rocks, trees or cliffs in the avalanche path. You can avoid the problem entirely by simply sticking to slopes less than 30 degrees. If you do get out and assess this weak layer, consider taking the time to submit an observation. That will help us paint a better picture of how well this layer is healing.

A sample of the buried surface hoar from Tenderfoot yesterday. This is outside of our advisory area, but the structure was similar to what we’ve been seeing around Turnagain Pass and Girdwood. Photo Megan Guinn. 02.01.2023

Phil Connors would understand how we are feeling right now.

Additional Concern

Deep Persistent Slabs

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.

More info at Avalanche.org

It’s been nearly a month since the last confirmed activity on the Thanksgiving crust/facet layer. The layer hasn’t gone away, but at this point it is becoming very unlikely a person could trigger an avalanche that deep. As we continue in our stretch of very quiet weather, it is feeling appropriate to file this layer as an additional concern– something that is present in the snowpack but would be really surprising to see a person trigger an avalanche on it. If someone were to be able to find a spot to make a really big avalanche, it would be at a higher elevation in an area with a thin snowpack, where the weight of a person can still impact the weak layer. Things can change if we see a major loading event or a significant warming event down the road, but for now it is a layer we are tracking but not expecting to see any activity on.

Weather

Thu, February 2nd, 2023

Yesterday: Skies were mostly cloudy with light winds blowing 5-10 mph out of variable directions. Periods of precipitation brought a trace of snow in some parts of the advisory area, with snow to sea level. Temperatures were coldest yesterday morning, with lows in the low 20’s F and highs getting up to the low 30’s in the valleys and mid to upper 20’s at higher elevations.

Today: We’re expecting a similar day to yesterday, with mostly cloudy skies and periods of light snow bringing a trace to 2” snow during the day. Winds will be light out of the south with high temperatures in the upper 20’s F and lows in the low 20’s F.

Tomorrow: More of the same tomorrow, with cloudy skies and light winds out of the south. Temperatures should be a little cooler than today, with highs in the mid 20’s F and lows dipping into the high teens to low 20’s F. Light precipitation should only bring a trace of snow, with snow to sea level. Chances are still looking good for a more significant storm starting Sunday, stay tuned for more.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	28	tr	0	62
Summit Lake (1400′)	24	tr	0	34
Alyeska Mid (1700′)	30	tr	0.02	61
Bear Valley – Portage (132′)	29	tr	0.07	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	E	4	15
Seattle Ridge (2400′)	24	E	4	11

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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