Wed, January 19, 2022 Turnagain Pass Avalanche Forecast

Wed, January 19th, 2022

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

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.

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

Light snow is falling this morning bringing a nice ‘refresher’ to the mountains around Girdwood, Turnagain Pass, and even down toward Summit Lake. As of 6am, roughly 1-3″ has fallen with another 3-5″ expected through today before tapering off tonight. The easterly winds are blowing 10-20mph along the ridgetops with gusts near 30. The winds should remain through most the day and also quiet down tonight.

With this shot of snow and some moderate winds, we can expect wind slab development through the day. It’ll be important to keep a look out for slopes that are seeing active wind loading. Slabs that do form should be fairly soft and on the smaller and shallower side – up to a foot deep or so. They could be more easily triggered where they are sitting on a new batch of surface hoar that grew over the past few days. The winds also may pick up some older loose snow, which could add to the depth of the new wind slabs. Something to keep in mind if finding yourself in a particularly windy zone. As always, watch for signs of recent avalanches and cracking in the snow around you.

All in all, there are likely to be many areas that are sheltered enough from the winds to avoid the wind slab problem. Unless more snow falls than forecast, which would create a storm slab avalanche issue, we can expect small sluffs on steep slopes within the 4-8″ of new low density snow.

Graphic courtesy of the NWS showing snowfall totals through today.

Snow surface with a new crop of surface hoar. This photo is from the mid-elevations on Lipps, but small surface hoar was reported up to ridgetops. 1.17.22.

Additional Concern

Persistent Slabs

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.

More info at Avalanche.org

Thanks to the many folks writing in over the holiday weekend, we have a reasonable amount of information regarding the layers deeper in the snowpack. Evidence continues to show the snow surrounding the buried crusts (New Year’s crust and mid storm crusts from last week) are not reacting or producing avalanches. These crusts are anywhere from 1-5′ deep depending on location. They are degrading in shallower areas and are in general quite variable. Although they are not likely to cause an avalanche, there still could be an outlier lurking. This would most likely be a wind loaded slope (wind loaded during last week’s storm) and in a shallower snowpack zone where the old wind slab sits on weak snow over a crust.

Weather

Wed, January 19th, 2022

Yesterday: Overcast skies were over the region yesterday with easterly winds in the 10-15mph along ridgetops. Temperatures were in the teens along ridgelines and in the 20’sF at the lower elevations. Light snow began to fall around midnight with a slight bump in easterly winds.

Today: A weak front is pushing in from the south this morning bringing snowfall and moderate easterly winds along the ridgelines (10-20mph, gusts near 30). As of 6am, 1-3″ has fallen and we are expecting another 3-5″ through the day (snow to sea level). Temperatures are bumping up to near 30F at sea level and to 20F along the ridgelines.

Tomorrow: A break in weather is looking promising for Thursday with partly cloudy skies, mild temperatures and light to moderate east winds. A real pattern change (warm, wet windy weather….) heads in late Thursday through the weekend. Stay tuned as more precipitation is headed our way along with a rising rain line.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	26	2	0.2	80
Summit Lake (1400′)	22	1	0.1	29
Alyeska Mid (1700′)	24	3	0.2	63

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	17	NE	15	30
Seattle Ridge (2400′)	20	SE	11	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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