Wed, February 14, 2024 Turnagain Pass Avalanche Forecast

Wed, February 14th, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

Thu, February 15th, 2024

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

2 - Moderate

Thu, February 15th, 2024

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

A few wind slab avalanches were reported yesterday. These were small to large depending on the terrain. Pictured below is a small natural wind slab seen in the Tincan area. We do not have any more photos due to the poor visibility, but we can expect that many natural avalanches occurred in addition to the ones seen.

As mentioned above, there was a large human triggered avalanche in the Summit Lake area, to the south of the forecast zone. Details will be shared as soon as possible and forecasters will be visiting the site today.

Natural avalanche in the Tincan trees, likely released Feb 13 during stormy weather. Photo 2.13.2024

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 two days of very strong east winds, gusting in the 80s mph, winds are backing off ‘slightly’ today. However, they are still expected to be strong, 20 to 30 mph with 50+ mph gusts on ridgetops. Considering this is the third day of high winds, we can imagine several feet of wind blown snow has created sensitive wind slabs.

Wind slabs are not only to be found in the higher elevations above treeline, but the mid elevations including some treed slopes that are typically more sheltered. These slabs may be several feet deep and could overload a buried weak layer, which would create a larger avalanche. The stormy weather has made it difficult to see recent avalanche activity and with another day of winds and warming temperatures, choosing lower angle terrain if you decide to venture out today will be a good bet for avoiding an avalanche.

Cornices: Warming temperatures and strong winds should continue to build cornices and may push them to their breaking point. Even small pieces that break off can trigger a wind slab avalanche below.

Wet Avalanches and Sun Effect: Warmer air is streaming in today along with clearing skies that could bring sunshine. Both these factors could cause more melting in the snowpack in the lower elevations, and even possibly higher elevations on south facing slopes. In this case wet avalanches would be possible.

Strong winds blowing snow in the trees below Seattle Ridge. Photo 2.13.2024

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

The layer of sugary faceted snow from January is buried anywhere from 1-3’ deep. There is still limited information as to how reactive this layer is at Turnagain Pass and essentially, how easy it would be for a person to trigger a large slab avalanche. Snowpits have shown it to be most reactive at elevations between 1,000 and 2,000′, which is where a lot of traffic can take place during stormy weather. These areas include sheltered areas such as open areas in the trees.

We found the January faceted snow at 1,500′ at Turnagain Pass yesterday. The layer took a lot of force to make it fail, meaning it would be on the harder side to trigger it. But, we still do not have many data points and this concern deserves a conservative mindset.

Concerning results (propagating Extended Column Test at 21 and 27 taps) about 2′ deep in our pit on a sheltered slope at 1,500′ on the motorized side of Turnagain Pass. 2.13.2024

Additional Concern

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

It has been over two weeks since a glide avalanche was reported. However, glide cracks are still capable of releasing into an avalanche so it is recommended to avoid spending time under these cracks.

Weather

Wed, February 14th, 2024

Yesterday: Mostly cloudy skies, strong east winds, and light snowfall was seen above 1,000′ (light rain below 1,000′). Ridgetop winds were sustained at 25-40 mph with gusts between 50 and 90 mph. Between 2-6″ of new snow is estimated above 2,000′.

Today: Strong east winds will continue today with clearing skies and warming temperatures. Ridgetop winds are expected to be 20-30 mph with gusts 40-60 mph from an easterly direction. No precipitation is expected. Temperatures look to rise to near 30F along ridges today and into the 40s F at sea level.

Tomorrow: Another windy day with scattered showers and passing clouds is expected for Thursday. Ridgetop winds again will be easterly at 20-30 mph with gusts near 50. A trace to an inch of snow above 1,000′ is possible with rain below. More unsettled weather with mild temperatures is expected for the weekend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	32	2	0.4	88
Summit Lake (1400′)	36	0	0	43
Alyeska Mid (1700′)	33	0	0.2	97
Bear Valley – Portage (132′)	40	rain	0.76	–
Grouse Ck (700′)	36	rain	0.2	62

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	23	ENE	31	80
Seattle Ridge (2400′)	27	n/a	n/a	n/a

*Seattle Ridge wind sensor is rimed and not reporting.

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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