Sun, December 22, 2013 Turnagain Pass Avalanche Forecast

Sun, December 22nd, 2013

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

We had no reports of avalanche activity yesterday, however the visibility was poor and it looked as though most folks were staying in the trees and out of steep avalanche terrain.

Another small shot of precipitation has added 3-5″ of dense snow to our snowpack since Friday night and we have another 1-2″ possible for today. The new snow is sticking rather well to the surface but it’s the weak snow buried 12-16″ down that we are worried about. This new snow is not likely to be enough to overwhelm the buried weak layers but the added weight of a person could be. In fact, we know a person can overwhelm these weak layers by the widespread collapsing that continues at all aspects and elevations in the mountains. For a closer look at our weak foundation click this link and check out the video and see this report from the north side of the Pass.

For today, sticking to lower angle terrain, without steeper slopes above you, will be your best bet at avoiding a potential avalanche.

Avalanche Problem 2

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

Though the snow is heavy and wet at the parking lots on Turnagain Pass, it is dry at the upper elevations and able to be transported by the wind. Winds are forecast to shift and start bumping up from the Northwest by noon today and fresh wind slabs may start forming above treeline. This flow direction is prime for loading the Southeast face of Seattle Ridge – the slopes right above the motorized parking lot. By tonight the Northwest flow may reach over 50mph averages, so keep your eyes peeled in case the wind is ahead of schedule.

*Fresh wind slabs will have the potential to overload the weak snow deeper in the pack and larger and more dangerous avalanches could be triggered. Steer well away from any area with fresh wind deposited snow.

Weather

Sun, December 22nd, 2013

Yesterday we had light snowfall which turned to rain at sea level in the afternoon. We picked up around 3″ of heavy wet snow above 500′. Rain snow line was around 200′. Temperatures were in the mid 20’s at the ridgetop stations and low 30’s at sea level. Winds were blowing 10mph with gusts to 30mph from the East during the day and have dropped to ~5mph overnight.

During the past 36 hours precipitation totals: 3-5″ of heavy wet snow (.3-.6 water equivalent).

It will start out as another soggy day today but cool down by this afternoon as the warm area of low pressure over us moves off to the East. We might pick up 1-2″ of snow as this system exits. Winds should shift to the North by mid-morning and increase to the 15-20mph range. With this we should see the temperature drop to the teens on the ridges and mid 20’s at sea level.

On Monday skies should clear up and temperatures continue to drop back to the single digit range with the North flow. Another system looks to brush by us on Christmas Eve and Christmas.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
11/27/23	Turnagain	Avalanche: Tincan Ridge	Schauer/ Stiassny Forecaster
11/26/23	Turnagain	Observation: Road report: Slide with dirt on Repeat offender	Anonymous
11/26/23	Turnagain	Observation: Pete’s North	Ben Sullender
11/25/23	Turnagain	Observation: Tincan trees	John Sykes Forecaster
11/21/23		Observation: Spokane Creek	John Sykes Forecaster
11/20/23	Turnagain	Observation: Sunburst	Anonymous
11/19/23	Turnagain	Observation: Magnum – PMS Bowl	Schauer/ Cullen/ Jonas Forecaster
11/19/23	Other Regions	Observation: Sunnyside/Penguin	Jose Ramos-Leon
11/19/23	Turnagain	Observation: Eddies	Andy Moderow
11/19/23	Turnagain	Observation: Cornbiscuit	Anonymous

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