Fri, February 22, 2013 Turnagain Pass Avalanche Forecast

Fri, February 22nd, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

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.

Avalanche Problem 1

Dry Loose

Dry Loose

Dry Loose avalanches are the release of dry unconsolidated snow and typically occur within layers of soft snow near the surface of the snowpack. These avalanches start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-dry avalanches include point-release avalanches or sluffs.

More info at Avalanche.org

The storm that ended Wednesday left 6-8 inches of light density snow sitting on the surface. This snow will sluff easily today, primarily on North and West aspects and especially in steeper terrain. South and some East facing terrain received enough sun yesterday to melt the surface snow which has re frozen overnight where loose snow avalanches are less of a problem. Natural point releases were observed on multiple aspects above treeline yesterday. Expect more of the same today with sluffs being small to medium in volume. Pay particular attention to these above terrain traps such as cliffs, gullies and trees.

Wind slabs
There is the possibility of finding isolated older pockets of shallow wind slab in the higher elevation starting zones. Triggering one of these smaller slabs combined with sluffing will increase the volume of snow moving dowhill, making it harder to manage terrain appropriately.

Avalanche Problem 2

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

A distinct buried crust resides in many locations between ~1,500-3,000′ in elevation. On top of this crust is weak snow in some areas. On top of that weak snow is a slab up to 3 feet thick. Yesterday my partners and I tested the snow at this interface and found it to be non reactive. Other areas in the last week have shown this layer to be reactive and because of this it is still worth paying attention to. Staying off of steep rollovers and thin spots, especially slopes getting direct sun will help in avoiding this problem today.

We also looked at some thin spots in the snowpack to assess the deep slab problem. Weak snow still exists at the ground above 2,000′. Our tests yesterday showed this weak snow to be non reactive, for now.

Weather

Fri, February 22nd, 2013

In the past 24 hours the mountains around Eastern Turnagain Arm have picked up a trace of new snow. Winds have been very light out of the North and Northwest and temperatures have been in the teens at ridgetops. The sun made an appearance for several hours during the day yesterday and has created crusts on South aspects.

Today expect to see lingering snow showers giving way to clearing skies in the afternoon ahead of the next approaching disturbance. Winds will blow 10-20 mph out of the Northwest and temperatures at 1,000′ will be in the mid twenties.

Light snowfall should resume late tonight as a series of weak disturbances continue to move through the area over the next several days.

___________________________________________________

Kevin will issue the next advisory tomorrow morning, February 23rd.

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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