Sat, December 10, 2022 Turnagain Pass Avalanche Forecast

Sat, December 10th, 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.

Recent Avalanches

Turnagain Pass: We saw a bunch of fresh wind slabs releasing naturally yesterday as the strong outflow winds gained enough strength to start reaching into the lower elevations in the Turnagain Pass area. Most of the activity we observed was along the South and East aspects of Seattle Ridge, but that is also where there was good light for viewing avalanches so there were likely many more hiding in the shadows. Here are a few examples, see this observation for more photos.

Natural wind slab on the E aspect of Seattle Ridge at about 2500′. Photo 12.9.22

Partially filled in wind slab along the E aspect of Seattle Ridge at 2600′. Photo 12.9.22

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

After several days of outflow winds, they finally built up enough wind speed to reach into the treeline elevations of Turnagain Pass yesterday. We observed several natural avalanches along Seattle ridge and saw active transport along all the ridgelines in the area. Surface conditions range from soft snow in protected areas to areas where the wind has blown off all the fresh snow down to a melt freeze crust.

The main concern for today will be lingering wind slabs 1-2′ deep from yesterdays wind event. These are most likely to be found on the leeward side of ridgelines and wind loaded gully features. The distribution of wind slabs in Turnagain Pass is more widespread than the past several outflow wind events because the winds affected lower elevation terrain yesterday.

To identify features that are potentially holding onto lingering wind slabs it is important to step out of the skin track and feel the surface snow conditions around you. Look for stiff and hollow feeling snow on the surface and areas where the winds have transported the snow into large drifts or pillows. Using small test slopes can be a good way to see how reactive wind slabs are before committing to more consequential terrain. These wind slabs were deposited on top of a layer of surface facets which could make them release on lower angle slopes and remain reactive for longer than normal.

Using a small test slope to check how reactive wind slabs were yesterday. This feature on Sunburst easily produced shooting cracks and small pockets of wind slab. Photo 12.9.22

Slippery skinning conditions along Sunburst ridge where the winds stripped off all the fresh snow down to a melt freeze crust. Photo 12.9.22

Weather

Sat, December 10th, 2022

Yesterday: Clear, cold, and windy. Winds were averaging around 10 mph out of the NW in Turnagain Pass with gusts to 20-30 mph. Much stronger winds were transporting snow along upper elevation ridgelines and in areas exposed to gap winds.

Today: We are transitioning from cold and clear with outflow winds to the onset of our next storm. Winds will switch to the South and decrease to 5-10 mph this morning. Temperatures will remain in the single digits to low teens. Cloud cover is expected to move into the area today, starting at higher elevations and gradually descending. Snowfall associated with our next system should start either late tonight or early Sunday morning.

Tomorrow: Heavy snowfall is expected on Sunday. Depending on the timing of the storm we could see anywhere from 6-12″ during the day on Sunday. From Sunday morning through Monday afternoon we are expecting 2-4′ of new snow, with higher totals in coastal areas. Temperatures will increase to the teens to low twenties on Sunday, and snowline is expected to remain at sea level. Winds are also expected to increase with the storm, with averages in the 30-40 mph range and gusts of 60+ mph.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	15	30
Summit Lake (1400′)	14	20
Alyeska Mid (1700′)	14	28
Bear Valley – Portage (132′)	21	–

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	6	WNW	10	34
Seattle Ridge (2400′)	13	NW	9	30

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

Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.