Sat, February 13, 2016 Turnagain Pass Avalanche Forecast

Sat, February 13th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

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

Glide Avalanches

Glide Avalanches

Glide Avalanches are the release of the entire snow cover as a result of gliding over the ground. Glide avalanches can be composed of wet, moist, or almost entirely dry snow. They typically occur in very specific paths, where the slope is steep enough and the ground surface is relatively smooth. They are often proceeded by full depth cracks (glide cracks), though the time between the appearance of a crack and an avalanche can vary between seconds and months. Glide avalanches are unlikely to be triggered by a person, are nearly impossible to forecast, and thus pose a hazard that is extremely difficult to manage.

More info at Avalanche.org

Our primary concern continues to center around glide avalanches. These are popping out both small and large over the past several days. They are mostly in the mid-elevation band and the warm weather has kept them active. The last known glide crack to release on Turnagain Pass that we know about, releasing in areas people recreate, was two-three days ago on Eddies Ridge. The only way to manage this avalanche problem is to limit, or avoid, time under glide cracks.

Photo below: Glide cracks and one release on Peak 3640′ just Southeast of Gilpatrick in the Summit Lake zone.

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

Over the past two days we have seen 1.5+” of rain fall up to 2,500, possibly higher in some areas; this is the highest rain line we have seen this season. Yesterday afternoon temperatures at treeline (2,400′ on Tincan) reached 34 degrees! The snowpack is slowly decreasing at the mid-elevations, but there is still plenty to ride out this warm spell.

Wet avalanches continue to be a concern. With little visibility yesterday we are uncertain as to the extent of any natural wet activity. As the temperatures remain warm, the rain-on-snow will continue to weaken the snowpack and naturally occurring wet loose, and even some wet slabs avalanches, are possible. These slides can be quite large on sustained slopes such as the East face of Seattle Ridge. Steering clear of runnout zones will be key if you are getting out today.

Left photo: Tincan Ridge, still plenty of snowcover despite the rain. Right photo: The motorized lot is slick but has been plowed out nicely.

Additional Concern

Storm Slabs

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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

At the high elevations where it is snowing (this is above 2,500′) there are a variety of storm snow avalanche issues:

Storm Slabs: This warm, wet snow should bond quickly to the surfaces below but the warmer snow over slightly colder snow may create storm slabs. Quick hand pits are a good way to determine if the new snow is sticking to the old snow.

Wind slabs: Over the past two days we have received 15-20″ of new snow with sustained winds. Although wind slabs are stabilizing quickly with the sticky snow, it may still be possible to trigger a wind slab in steep wind-loaded terrain. Be on the lookout for stiff, pillowed snow and shooting cracks.

Cornices: The fresh snow/wind combination will also add to already large cornices that may be very tender due to warm temperatures. Avoid travel on or below these behemoths.

Weather

Sat, February 13th, 2016

Yesterday was another mostly cloudy day with rain falling off and on at the Pass. Around .5″ of rain fell up to 2,500′ with ~5″ of wet snow above this. Ridgetop winds were strong to moderate through the day from the East and were blowing in the 20-35mph range. Temperatures were warm….up to 35F at 2,000′. This is all due to a series of low-pressure systems moving over us and entraining warm and moist air from the South.

Overnight, light precipitation has continued and temperatures have remained warm. The rain/snow line looks to have dropped slightly to 2,000′. Another shot of precipitation and wind is on tap again today. It has been difficult determining how much precipitation will make it over the mountains from PWS, but so far we seem to get a bit more than forecast. We may see up to .5″ today and another .5″ tonight, with the rain/snow line between 1,800 and 2,000′ (equating to another 5-10+” in the Alpine). The Easterly ridgetop winds should pick up again to the 25-35mph range with stronger gusts.

For Sunday, this warm and wet weather pattern looks to continue.

PRECIPITATION 24-hour data (6am – 6am)

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	rain	0.5	105
Summit Lake (1400′)	35	rain	0.1	30
Alyeska Mid (1700′)	34	rain	0.6	86

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	NE	21	51
Seattle Ridge (2400′)	28	–	–	–

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/14/24	Turnagain	Observation: Sunburst	T. Olsen-Lund, R. Sullivan I. Adams
04/14/24	Turnagain	Observation: Turnagain Pass Snomo	K. Gallaher
04/13/24	Turnagain	Observation: Spokane Creek	Everet Megli
04/11/24	Turnagain	Observation: Tincan	John Sykes Forecaster
04/10/24	Turnagain	Avalanche: Seattle Ridge	Schauer/ Keeler Forecaster
04/10/24	Turnagain	Observation: Cornbiscuit South Face	Todd Kelsey
04/10/24	Turnagain	Avalanche: Tincan	N. Dumont J. Carlberg
04/10/24	Turnagain	Avalanche: Cornbiscuit	Tyler Grundstrom
04/07/24	Turnagain	Observation: Seattle Creek Headwall	Troy Tempel

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