Sun, December 07, 2014 Turnagain Pass Avalanche Forecast

Sun, December 7th, 2014

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

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

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

It is the dreaded rain-on-snow that is in our future today, and into the early part of the week. With climbing temperatures overnight and periods of heavy rain expected at sea level, the question is, “How high will the rain get?” The answer is, 1,200′ for sure, likely 1,500′ at times and possibly a bit higher.

Wet loose snow avalanches will be the most likely type of wet avalanche to be triggered. These can entrain significant amounts of heavy dense snow if the slope is sustained and steep enough (> 35 degrees). If you are getting out today, watch for areas where the snow is becoming saturated and heavy. Steering clear of steep saturated slopes will be good ways to avoid a wet sluff. Also, keep in mind terrain traps, such as steep narrow gullies in the Tincan Trees. These steep walled and narrow terrain features can pose a threat if even a small amount of heavy snow slides down onto you.

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

In the Alpine terrain, above treeline, we are expecting around 6-10″ of wet to moist snow to fall. Along with this, winds are forecast to be strong from the East and Northeast which will quickly form wind slabs, drifts and cornices. The warm nature of the new snow will allow it to bond rather quickly to the preexisting surface, however with the rapid loading expected today, be wary of fresh slabs and drifts. Watching for current wind loading and cracks shooting from your skis/board will be good ways to suss out if slabs are sensitive.

Additional Concern

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

It is time to put glide avalanches back on our radar. With warming temperatures we could see a number of glides cracks open up and release in the next several days. Yesterday, we saw a slab that has moved during the past week and looks ready to avalanche. Staying out from under glide cracks will be key this week.

Glide slab in the Seattle Creek drainage (East facing ~2,000′).

Weather

Sun, December 7th, 2014

Weather yesterday was relatively mild with overcast skies, light winds from the East and Northeast and only a trace to an inch of snow accumulating above 1,000′ (rain below).

Overnight, temperatures and winds have increased at all elevations as the leading edge of a large and complex low pressure system moves in from the Gulf. We can expect up to an inch of rain to fall throughout the day below 1,500′ with 6-10″ of wet snow above. Winds have already begun to climb and will be blowing from the East in the 35-45mph range. Temperatures are also climbing and should top out around 30 deg. F on the ridgetops and the upper 30’sF at 1,000′ on Turnagain Pass.

For Monday, precipitation intensity will diminish slightly with forecast amounts around .5″ of rain and 3-5″ of snow (rain/snow line ~1,200′). Winds will continue from the East and should diminish slightly as well. Temperatures will remain warm, near 30F on the ridgetops and the upper 30’s at 1,000′. It looks as though it will be Wednesday before temperatures cool back off for snow to make it down near sea level.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	34	1	0.1	20
Summit Lake (1400′)	33	0	0	5
Alyeska Mid (1700′)	33	1	0.22	17

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	29	E	16	55
Seattle Ridge (2400′)	29	NE	18	46

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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