Tue, February 05, 2013 Turnagain Pass Avalanche Forecast

Tue, February 5th, 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

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

There were a couple very small skier triggered wind slab avalanches yesterday on freshly wind loaded rollovers/wind lips near treeline. One natural wind slab, a bit bigger (30-40’ across, ~1′ deep and running around 150’), was seen in a cross-loaded gully on the east face of Seattle Ridge (looker’s left of the motorized “up-track”). Keep in mind, the low visibility kept folks to the mid and lower elevations leaving the upper, and more concerning, slopes untouched.

Today, triggering a lingering wind slab will be the primany concern. The wind has backed off considerably this morning but it did load its fair share of slopes over the past several days. These slabs are most likely to be 1-2 feet in depth and found just off ridgelines, rollovers and cross-loaded in gullies. Watching for smooth “pillowy” surfaces, hollow feeling snow and cracking in the snow around you will be keys to recognizing these slabs. With the potential for good visibility today and travel to steeper slopes, even a small avalanche triggered can be dangerous if one gets washed into a terrain trap (i.e., over a cliff or into a gully).

Cornices: With several days now of warm temperatures, snow and wind, cornices have been building. Giving these monsters a wide berth will be prudent as they could be close to the tipping point.

Below treeline: It will be unlikely to trigger an avalanche below treeline. A few inches of low density snow sits on multiple crust layers that extend up to 2,000’-2,500’. The most recent crust was formed February 2^nd and is somewhat breakable with a stouter rain crust from 1/30 below.

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

Ah, the deep slab problem… Yes, it has been 3 weeks now since the last deep slab avalanche and yes, it would be nice to put this broken record away, but time will tell. We have been tracking the weak October and November facets at different elevation bands the past couple days. These are buried 4-7’ deep in general and continue to show gains in strength. Reports from the 2,400′ and 3,000’ band show the facets remain dry and intact but are rounding, bonding and gaining in hardness. This is all good news and what we want – but these pits are only small snapshots. Due to the severity of this type of avalanche, and the rule that facets can come back to bite one, it is a guilty untill proven innocent situation. In the mean time, steering clear of thin spots, exposing only one person at a time and moving efficiently through avalanche terrain are good practices.

Weather

Tue, February 5th, 2013

Over the past 24 hours we have seen a trace to an inch of new snow with moderate to strong easterly wind. Skies have been overcast and temperatures mild, in the 30’s below treeline and mid 20’s on the ridgetops.

Today we should see a break in precipitation, wind and cloud cover. The sun is even on tap to make an appearance. Wind has backed off and barely blowing, in the 0-10mph range, from the east where it should remain light but shift to the northwest during the day. Temperatures look to remain in the low 30’s at 1,000′ and mid 20’s on the ridgetops.

Tomorrow looks like clouds will head this way again as the next system pushes in from the southwest for another shot of precip on Thursday.

Kevin will issue the next advisory tomorrow morning, February 6th.

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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