Fri, March 20, 2015 Turnagain Pass Avalanche Forecast

Fri, March 20th, 2015

Alpine

Above 2,500'

3 - Considerable

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

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

In the Alpine above 2500’ a slab 2-3’ has formed over the last four days. The majority of this snow fell on March 16th, but strong Northeast winds and additional precipitation have likely made slab depths closer to 4-5’ on leeward starting zones. Below this slab lies weak faceted snow sitting on a crust bed surface. This weak layer was very touchy on Tuesday, but as we move away from the initial loading event the slab has become denser and more supportable. The scary part about this avalanche problem is if the right trigger point was found the consequences could be very serious. Obvious signs like shooting cracks, collapsing and natural avalanches might not be present today making it easier for us humans to be lured into steeper terrain.

Today’s travel advice is simple: Avoid traveling in steep terrain and keep your slope angles under 35°.

The combination of sunny beautiful weather following a four-day storm cycle is our biggest hazard today. It will be tempting to venture into bigger terrain making it easy to “talk yourself” into thinking the conditions are more stable than they really are. Here are some classic traps to be aware:

“Someone just skied that line and it didn’t slide.”

“I’ve skied this slope a 100 times and I’ve never seen it slide.”

“Our snow pit results were good, therefore this slope must be safe.”

“I just heard/felt a “woomph”, but my partner has a lot more experience than I do and he/she doesn’t seem to be concerned.”

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

Two days of Northeast winds averaging 30-40 mph have loaded South and Western slopes and fresh wind slabs up to 2’ thick could be easy to trigger on leeward features. If a wind slab is triggered it could be enough force to initiate the larger problem described above. This will be an additional reason to avoid steep terrain.

Additional Concern

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

If temperatures reach the mid 40’s F as forecasted for today, wet point-release avalanches on sun-exposed slopes are possible. They will likely be seen on steep Eastern aspects first and then on Southern aspects as the Sun moves throughout the day.

There is currently a lot of water draining through the snow pack at mid elevations and temperatures could be warm enough to start meling the newly formed surface crust. It is possible that a small point release from the Alpine could pick up enough volume and momentum to entrain wet snow at this elevation band. Today might be a good to day to avoid places like Seattle Ridge where access into and out of the Alpine is on a steep Eastern slope.

Yesterday large puddles and flowing water were observed near the road along the Seward Hwy in Turnagain Pass.

Weather

Fri, March 20th, 2015

Yesterday we received 0.7 € of water in Turnagain Pass. Rain/snow line was near 1500′ and temperatures below this elevation averaged in the mid 30’s F. At higher elevations temps were in the mid to high 20’s F and snow accumulation was likely around 7 €. Winds were 30-40mph from the Northeast along ridgetops.

Overnight skies cleared and no new precipitation fell. Temperatures dipped into the low 30’s F at mid elevations and NE winds were 15-20 mph.

Today will be mostly sunny and day-time temperatures could reach the mid 40’s F. Ridgetop winds will be 5-15 mph from the East and no new precipitation is expected today.

Tomorrow there is a chance for rain showers at lower elevations. Temperatures are expected to remain warm, high 30’s to mid 40’s near sea level. This could mean snow in the upper elevations, but not much accumulation is expected. Winds will be light to moderate from the East along ridgetops.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	33	0	.7	56
Summit Lake (1400′)	34	0	.1	12
Alyeska Mid (1700′)	34	0	.22	35

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	ENE	22	68
Seattle Ridge (2400′)	27	NW	18	50

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster

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