Sun, March 21, 2021 Turnagain Pass Avalanche Forecast

Sun, March 21st, 2021

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

Persistent Slabs
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.

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

Our main concern today is the lingering potential to trigger an avalanche 1-3’ deep on the layer of buried surface hoar and near-surface facets that were buried about two weeks ago. As we move further out from the last major loading event, these weak grain types are slowly gaining strength, becoming more stubborn and difficult to trigger. Although the likelihood for triggering these avalanches is decreasing, we still do not have the confidence to forget about this problem. The most likely place to run into trouble will be in terrain that has been recently wind-loaded, with relatively stiff snow sitting on top of relatively soft snow. It may also be a bit more sensitive on steep southerly aspects, where there are weak facets above and below a sun crust that formed earlier in the month. If you are trying to step out into steep terrain today, you can minimize your risk by being mindful of safe travel protocol:

Make sure only one person is exposed to steep terrain at a time. Regroup in safe zones out of the way of avalanche paths and runout zones.
Avoid steep slopes with terrain traps that will increase the consequences of triggering even a small avalanche.
Pay attention to warning signs of poor stability. This includes recent avalanche activity, cracks shooting out from your machine or feet, and collapsing or ‘whumpfing’.

Wind Slabs: Winds have shifted back to the northwest. With speeds expected to stay in the 5-15 mph range, we might see some smaller wind slabs forming today. Be on the lookout for signs of wind loading, and avoid steep slopes that are being actively loaded.

Sluffs: Steep slopes that have been sheltered from the wind have around a foot or more of loose snow sitting on top of firm surfaces. It will be easy to trigger dry loose avalanches today, and they can pick up enough volume and speed to carry a person. While it is unlikely they will be big enough to bury you, they can be dangerous if they drag you into terrain traps like cliffs, trees, rocks, or gullies.

Buried weak layers in the upper snowpack from a snowpit in Zero Bowl. 03.21.2021

Weather

Sun, March 21st, 2021

Yesterday: Skies were cloudy with high temperatures in the low teens to upper 20’s F. Low temperatures were in the single digits to mid teens F, and all the way down to -8 F near Portage yesterday morning. Easterly winds were 5-15 mph at ridgetops with gusts to 33 mph. No precipitation was recorded.

Today: We are expecting mostly sunny skies as winds shift back to the northwest at 5-15 mph. High temperatures are expected in the upper teens to mid 20s F, with lows in the single digits to low teens F tonight. No precipitation is expected today.

Tomorrow: Winds are expected to be calm for most of the day, increasing slightly and shifting back to the east in the afternoon. Skies are expected to start out mostly sunny, with increasing cloud cover in the afternoon. High temperatures are expected to be in the upper teens to mid 20s F, and no precipitation is expected.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	21	112
Summit Lake (1400′)	17	45
Alyeska Mid (1700′)	20	115

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	9	NE	10	33
Seattle Ridge (2400′)	13	SE	8	25

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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