Mon, November 28, 2022 Turnagain Pass Avalanche Forecast

Mon, November 28th, 2022

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.

Avalanche Problem 1

Wind 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

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

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 will be triggering an avalanche on wind slabs that formed during the past few days of northwest winds. For the next few days, it is looking like our advisory area is going to see lighter winds than most of the rest of Southcentral. During this quiet spell, the stability will depend on how quickly those wind slabs that formed over the weekend heal. In some places these wind slabs buried a layer of surface hoar (details in this observation from Eddie’s), which would make them stay reactive longer than usual.

Safe travel today will require some work. Avalanche conditions will be more dangerous on slopes that were wind loaded over the weekend. The most suspect terrain features will be near ridgelines, convex rollovers, and in gullies. That northwest wind pattern will load slopes where we don’t always expect to see wind loading, so be on the lookout for dangerous conditions in unusual places. Seek feedback from the snowpack as you travel to see if those lingering wind slabs are still reactive. This can mean stepping off the skin track to feel for stiff snow on top of softer snow, or using test slopes to see if you can get shooting cracks or a small wind slab to fail. Be on the lookout for shooting cracks or collapsing as you travel. Any of these pieces of evidence would indicate unstable snow. Luckily, for now the best snow conditions will also be the most stable. This will be on slopes that are sheltered from the wind, with soft snow on the surface.

The front side of Seattle Ridge has some great examples of terrain features where you might find unstable wind slabs today. 11.27.2022

This little chunk of a wind slab on a micro terrain feature shows that wind slabs were still reactive yesterday. Small terrain features that could not produce an avalanche large enough to injure a person are a great way to get some snowpack feedback. 11.27.2022

Avalanche Problem 2

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

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 surface problems mentioned above, we are tracking that layer of facets at the ground that formed in October. It is becoming less likely to trigger an avalanche on this layer, but we still can’t rule it out. It seems like this layer is more of a concern at elevations above 3000′. It is unclear just how reactive the layer still is, so for now we should be careful with snowpack evaluation and terrain use in the high alpine. This means choosing routes that minimize exposure and as always, only exposing one person at a time to steep avalanche terrain. If you are trying to get into steeper terrain during this spell of decent weather, it is worth taking the time to dig a quick pit and look for that weak snow right at the bottom of the snowpack.

Weather

Mon, November 28th, 2022

Yesterday: Northwest winds backed off a bit yesterday, with ridgetop speeds around 5-15 mph and gusts of 15-30 mph. Skies were clear and high temperatures were in the teens F, with overnight lows in the single digits to low teens F.

Today: Expect quiet and cold conditions today. Scattered clouds should clear up through the day, with high temperatures in the low teens F and overnight lows in the single digits above and below 0 F. Winds will be light out of the north at around 5 mph. No precipitation is expected for the next few days.

Tomorrow: Cold and clear conditions continue, with daytime high temperatures in the single digits to mid teens F and overnight lows staying in the single digits. Winds should be around 5-10 mph out of the northwest with mostly sunny skies.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	12	25
Summit Lake (1400′)	8	14
Alyeska Mid (1700′)	12	21
Bear Valley – Portage (132′)	17	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	5	W	7	23
Seattle Ridge (2400′)	10	NW	5	21

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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