Thu, January 21, 2021 Turnagain Pass Avalanche Forecast

Thu, January 21st, 2021

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

As mentioned above in the bottom line, a snowmachiner was caught and carried in an avalanche at Snug yesterday. This is out of the forecast area. We hope to get more information on this close call today.
There was a small skier triggered wind slab on Tincan on a NW slope below Common Bowl and a small skier triggered wind slab on Magnum west face yesterday.
Small skier triggered wind slab, NW Tincan below Common Bowl, 1.20.21. Photo: Kellie Okonek.

Avalanche Problem 1

Wind Slabs
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.

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

With easterly ridgetop winds remaining elevated today, human triggered wind slabs will continue to be the concern. There is still soft snow to transport. Yesterday observers reported gusty ridgetop winds and blowing snow. There were two small skier triggered wind slabs that were 3-6″ deep. With additional wind-loading overnight and today the wind slabs could be 1-2′ deep. These will found in wind exposed terrain on steep unsupported slopes and cross-loaded gullies. You may be able to travel out onto the slab before it breaks above you, as is often the nature of hard wind slabs. Even a small slab can be very dangerous if you are in high consequence terrain. Looking for signs of wind effect and wind slab habitat will be key to safe travel today.

What to look for:

Wind texture and stiff snow
Rounded and pillow-like surfaces (wind deposited snow)
Hollow feeling or drum-like feeling on the snow due to stiff snow over softer snow
Cracks in the snow that shoot out from your machine, skis or board
Any collapsing in the snow or ‘whumpfing’

From Monday’s storm there is around 2′ of snow on a weaker storm snow interface. This interface, which was the low density snow from 1/15 and buried on 1/16, was the likely culprit in many of the natural avalanches that occurred on Monday. This interface is showing signs of bonding but a person triggering a large slab that breaks 2′ or more below the surface is still possible. Additional wind-loading may add stress and at this point it may be a situation where an avalanche fails with tracks already on the slope or if multiple people are on the slope at the same time. As always, practice safe travel protocols and expose only one person at a time.

Cornices: These are now very large and dangerous and there were a number of cornice falls during the storm on Monday. Some cornices are very wide along ridgelines and it is easy to not notice you are traveling out onto one. Be sure to give them an extra wide berth and know where you are in relation to them. They often break farther back than expected. The cornice at top of the Seattle Ridge up-track is one of these monsters to watch out for. Limit time spent underneath cornices as well. With continued wind-loading there is a chance one may fall naturally, which is dangerous on it’s own but could also trigger a wind slab on the slope below.

Blowing snow along the Sunburst ridge, 1.20.21

Cracking along a small wind-loaded feature on Sunburst, 1.20.21.

Weather

Thu, January 21st, 2021

Yesterday: Skies were mostly cloudy trending to partly cloudy skies with very light rain/snow showers in the morning. Rain/snowline was around 300′. Winds were easterly 15-25 mph with gusts into the 30s and 40s and eased a bit in the afternoon. Temperatures were in the 20°Fs in the alpine and the mid 30°Fs at sea level. Overnight skies remained partly cloudy and temperatures were in the high 30°Fs at sea level and the mid 20°Fs at ridgetops. Winds were easterly 10-15 mph with gusts into the 20s and 30s.

Today: Skies will partly to mostly cloudy with snow and rain showers in the afternoon. Winds will be easterly 10-20 mph with gusts into the 30s. Temperatures will be in the mid 30°Fs at 1000′ and mid 20°Fs in the alpine. Temperatures cool slightly overnight and snow showers continue. Winds remain easterly 10-20 mph with gust into the 30s.

Tomorrow: Another day of mostly cloudy skies with snow and rain showers and east winds 10-20 mph gusting into the 30s. Temperatures will be similar to Thursday. Winds and precipitation look to increase overnight as a front pushes into the area.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	31	134
Summit Lake (1400′)	27	47
Alyeska Mid (1700′)	31	134

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	21	NE	14	50
Seattle Ridge (2400′)	25	E	10	23

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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