Mon, February 10, 2014 Turnagain Pass Avalanche Forecast

Mon, February 10th, 2014

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

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 bump in wind this morning will be the main player in the avalanche game today. There has been a change in the weather overnight and skies are cloudy with a chance for 1-2″ of snow. The winds have just begun to increase from the East and are expected to reach the 25-30 mph range before decreasing this afternoon. Though this is a relatively small bump in wind with little new snow, we do have ample light snow available for transport – especially in the Turnagain Pass area. This is from Friday’s localized snow storm that deposited up to 18″ on Turnagain Pass.

The real concern, however, is how the wind may form slabs that can overload the weak faceted snow which sits underneath the recent storm snow. Friday’s storm snow has become very loose due to Saturday and Sunday’s clear and cold weather (see a couple more obsevations sent in yesterday HERE and HERE). This has decreased the slab properties that were present on Saturday and subsequently no new avalanche activity was seen on the Pass yesterday. Today’s winds however could change that by forming new wind slabs. Any fresh slabs formed have the potential to be quite sensitive to human triggers as they will be be sitting on weak snow.

For anyone getting out today, keep an eye out for areas where Friday’s snow is cohesive and especially where it is supportable to your weight. Watching for recent wind deposited snow, cracking or collapsing as well as quick hand pits are good ways to assess this.

Avalanche Problem 2

Deep Persistent Slabs

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.

More info at Avalanche.org

At the upper most elevations, weak snow exists near the ground under the majority of the snowpack (4-6+’ deep). This is responsible for the deep slab problem. There is a low likelihood of triggering a deep slab in comparison to the shallow persistent slab. However, the possibility lingers for triggering a slab that can pull out snow to the ground. Avoiding likely trigger points, especially areas where slabs are thinner, will lower the likelihood of triggering a deep slab avalanche.

This problem is not a concern below 3000ft where the previously water saturated layers have now frozen into a very strong and stable crust layer.

Weather

Mon, February 10th, 2014

Clear skies and ample sunshine greeted folks that were out yesterday. Winds were calm and though temperatures were in the 10F range, it felt quite warm. Valley bottoms remained cold and in the single digits.

Overnight, clouds have moved in and a trace of snow has fallen with a possible 1-2 inches expected through the day. Winds have just starting to increase this morning and are forecast to be in the 25-30 mph range with stronger gusts from the East. Temperatures should increase as well to 20F at 1,000′ and the low teens on the ridgetops. This change in weather is due to a low pressure center spinning in the Northern Gulf that is just strong enough to send a bit of moisture our way.

This system should exit this afternoon and a return to dry weather and mostly sunny skies are in store for Tuesday and Wednesday. For later in the week, we might start seeing more of a classic wintertime pattern with a low setting up over the Aleutians – which means possible snow in the forecast.

Sun effect?
Believe it or not the sun has been able to create a crust on southerly slopes. This was seen mainly in the mid and lower elevations (2,500′ ish).

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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