Sat, January 14, 2023 Turnagain Pass Avalanche Forecast

Sat, January 14th, 2023

Alpine

Above 2,500'

3 - Considerable

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

No new avalanches were reported yesterday. The last known activity was from the 4-6″ of new snow that fell on top of buried surface hoar on Tuesday night. This layer produced several small avalanches that were reactive to human triggers on Wednesday and Thursday. It has been 1 week since the last human triggered avalanche on a layer of buried facets 3-6′ deep on Cornbiscuit. Check out the Near Miss Report here.

Avalanche Problem 1

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

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

Human triggered avalanches 3-6′ deep on the Thanksgiving facet and crust layer remain our biggest concern. Deep persistent avalanche problems tend to take a long time to go away and can be dormant for long periods before producing very large avalanches when they get a new snow load or a trigger hits the wrong spot. When the skiing and riding conditions are good it can be hard to be patient and stay off avalanche terrain to give these layers time to heal.

To avoid this avalanche problem we are still recommending that people stick to small terrain features and low angle slopes if you are travelling at upper elevations. The most likely place to trigger a deep slab avalanche is from a thin spot in the snowpack, like where a rock is penetrating part way through the snowpack or wind scouring has created a shallower snowpack in specific areas. Using stability tests to assess deeply buried weak layers is notoriously unreliable, and is most likely to give a false sense of confidence. Last week there were several remote triggered avalanches on this layer, which means skiers or riders triggered avalanches from lower angle terrain onto steeper terrain around them. Being aware of steeper slopes above you and whether you are travelling in the runout zone of an avalanche path is important with remote triggers as a possibility.

Avalanche Problem 2

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

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

A storm moving into the area this morning is expected to bring 2-3″ of new snow during the day and elevated winds in the 10-20 mph range with gusts up to 30-40 mph. Wind slabs up to 1-2′ deep are likely with these moderate winds and could be more sensitive to human triggers than normal and propagate wider than normal due to a layer of surface hoar buried 4-6″ below the snow surface. Wind slabs are most likely at upper elevations along ridgelines and cross loaded gully features.

To assess whether wind slabs are an issue where you are travelling you can get off the beaten path to feel for hollow and wind affected snow and dig quick hand pits to look for buried surface hoar. Small test slopes can also be effective to evaluate if wind slabs are reactive in the area you are travelling. It is possible that triggering a smaller wind slab at upper elevations could trigger a larger avalanche on a buried weak layer.

NWS snowfall predictions from Saturday at 6am to Sunday at 6am. Graphic courtesy of NWS Anchorage 1.14.23

Weather

Sat, January 14th, 2023

Yesterday: Mostly cloudy with occasional breaks in the cloud cover. Warms temps in the 20s to 30s F. No measurable new snow. Winds speeds were light in the 0-10 mph range with some gusts up to 20mph at ridgetops.

Today: Light snowfall is expected to start this morning with 2-3″ in Girdwood and Turnagain Pass today and closer to 4-6″ in coastal areas like Portage and Placer. Snow line should be between 500 – 1000′ today. Wind speeds should increase with the start of snowfall with averages of 10-20 mph and gusts of 30-40 mph.

Tomorrow: By Sunday morning the new snow totals should be 6-8″ in Girdwood and Turnagain Pass with 8-12″ in coastal areas. Snow line is expected to remain between 500-1000′ throughout the weekend. Wind speeds should remain similar to Saturday with averages of 10-20 mph and gusts of 30-40 mph. Heavier snowfall is expected Sunday night into Monday with stronger winds, but forecast confidence is low past Sunday.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	30	–
Summit Lake (1400′)	25	32
Alyeska Mid (1700′)	30	52
Bear Valley – Portage (132′)	28	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	ENE	7	25
Seattle Ridge (2400′)	27	ESE	6	13

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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