Mon, December 31, 2012 Turnagain Pass Avalanche Forecast

Mon, December 31st, 2012

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

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

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

The past week has been a tough one for the snowpack. Weak unconsolidated snow close to the ground has been covered up with a very thick and heavy slab. With a break in the action today, those weak layers will get a (slim) chance to adjust to the new load. What this means is that triggering one of these deeply buried layers will be just slightly harder to do today. However, the fact remains that triggering one of these slabs will carry with it severe consequences. On Friday we were able to see evidence of the most recent avalanche cycle. Since then we have seen enough precip and wind to reload many of those areas. A few observations from yesterday reveal a snowpack that is still struggling to adjust to this newest load of snow and rain.

Avalanche Problem 2

Wet Loose

Wet Loose

Wet Loose avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

More info at Avalanche.org

Wet Slabs below 1500′
After a major shock to its system in the form of rain, the snowpack below 1500′ is very weak. I observed a handful of smaller wet slabs in the lower elevations yesterday. While they were smaller, they were still big enough to bury, injure or kill a person. With continued mild temps in the forecast today, it will be best to avoid avalanche terrain in areas where the thermometer reads above freezing.

Wind Slabs above 1500′
The last 24 hours has brought significant winds to the region. Above treeline today we should expect to see areas of newly formed dense wind slab to be sensitive to the weight of a person or snowmachine.

Weather

Mon, December 31st, 2012

The mountains have received rain up to the 1500′ elevation with snow above. Water amounts are in the .8 to 1 inch range. Winds have been blowing out of the East averaging 35 mph with gusts to 98. Temperatures have hovered above freezing at 1500 feet and been in the mid 20s at ridgetops.

This morning winds have calmed to the 20s, freezing level has dropped to the 1000′ elevation and precipitation has abated.

In the mountains today we will get a break in precip, with winds out of the east at 20 to 30 mph. Temperatures will remain mild with freezing line climbing back up to the 1500′ elevation.

Tonight and into tomorrow expect another shot of precip with up to a foot of new snow and wind to increase the likelihood of triggering avalanches.

Wendy will issue the next advisory on Tuesday morning, January 1st.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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