Mon, November 21, 2016 Turnagain Pass Avalanche Forecast

Mon, November 21st, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

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

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

More human triggered avalanches occurred yesterday with reports coming in from both Tincan and Sunburst, including the slope below Taylor Pass sliding. The buried layer of surface hoar continues to be the problem layer. It sits below the new snow from Thursday and has a few additional inches added from the weekend. Slabs have been soft and releasing while people are riding them as well as being triggered remotely from above or the side. With all the snow available for transport and an increase in wind speeds last night the slabs could be even more developed today, stiffer and more hazardous. Slab depths near ridgelines and in leeward areas could be deeper. Look for cracking in the snow, whumpfing and recent avalanche activity. Low angle slopes have been releasing which is a common with buried surface hoar. Pay attention to slope angle and what the terrain you traveling on is connected to, above and below. Avalanches were triggered onto and close to the skin track on Tincan both Saturday and Sunday. Please think about where you put skin tracks in and when you are descending make sure you are not skiing or riding on top of other people.

The new snow and wind will also make it harder to tell what slopes have slid already and wind slabs may be sensitive and exacerbate the problem. Today is another day to be conservative. Remember the buried surface hoar is widespread and is a persistent weak layer. This means it doesn’t heal/settle quickly and can be reactive for extended periods of time.

Backlit cross section of snow on Sunburst that shows the buried surface hoar. Photo W. Wagner

Looking up the skin track towards Tincan Common. Low angle avalanche from Saturday below the skin track.

Avalanche Problem 2

Wind Slabs

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.

More info at Avalanche.org

The winds have ramped over night gusting into the 40’s from the ENE. The light fluffy snow that we have enjoyed over the weekend will easily blow around and create fresh sensitive wind slabs that may or may not be sitting on the buried surface hoar. Wind slabs could be reactive either way and may make the slopes with surface hoar even more prone to avalanche. It will be important to pay attention to how the snow feels underfoot. Is it stiff? Does it feel upside down i.e. hard over soft? Do you see shooting cracks? Does it feel or sound hollow? Look for recent cornices, wind pillows and drifts. Remember recent wind is a RED FLAG and means something has changed. This is another reason to be conservative today. How are the mountains channeling the winds? Are slopes being wind loaded? Can you tell if the slopes are top loaded or cross loaded? Has the wind blown and affected the snow in the trees?

Photo: National Avalanche Center

Weather

Mon, November 21st, 2016

Yesterday was mostly cloudy with snow showers and a few windows of clearing. The winds were light and temperatures were in the low 20Fs. Overnight the winds picked up from the ENE blowing in the 20s and gusting into the 40s. Temperatures rose to the high 20s. 2-5 inches of snow fell in the last 24 hrs.

Today will be mostly cloudy with a chance of snow showers tapering off in the afternoon. 0-2 inches of snow possible. Winds will be in the 20s and gusty. These should also taper off during the day. Temperatures will be in the high 20Fs.

There is a clearing trend Tuesday into Thanksgiving Day with sunshine forecasted, light winds and temperatures in the 20Fs. An unsettled pattern returns over the weekend with a chance of snow.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	27	5	.4	21
Summit Lake (1400′)	27	1	.1	3
Alyeska Mid (1700′)	28	2.5	.2	5

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	22	ENE	22	44
Seattle Ridge (2400′)	23	N/A (sensor rimed)	N/A (sensor rimed)	N/A (sensor rimed)

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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