Mon, February 13, 2017 Turnagain Pass Avalanche Forecast

Mon, February 13th, 2017

Alpine

Above 2,500'

4 - High

Treeline

1,000'-2,500'

4 - High

Below Treeline

Below 1,000'

4 - High

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

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

New snow and wind have combined to create very unstable slabs, 1-3’ thick. Ridgetop winds from the East (SE to NE) picked yesterday afternoon and ramped up into the 40s and 50s mph overnight with several gusts in the 90s at Sunburst weather station. An additional 5-15″ of snow is forecasted for the higher elevations today and will increase the size of these slabs. These slabs will release naturally in steep terrain and could step down into older layers in some locations. Natural avalanches could run the full length of a slope, thus it will be important to avoid being near any runout zones today. Winds and continued precipitation will make natural avalanche activity likely throughout the day. There is some uncertainty with rain/snowline today. It is already 32F at Center Ridge and raining in Girdwood. Rain may fall as high as 2000′ today and the warming trend is forecasted to continue into tomorrow. Rain on snow will also increase the likelihood of natural avalanche activity at lower elevations. It is important to remember that the heavier, wetter new snow and/or rain is falling on lighter low density snow from Friday’s storm and loading a layer of buried surface hoar and small facets. Avalanche activity is expected at all elevations and aspects. This set up could be a hazard even in the Tincan Trees.

This is not a complicated situation. Avoidance of avalanche terrain is the only way to “manage” this problem today.

Sunburst Weather Station this morning. Strong winds and dramatic temperature increase. Note the gusting into the 90s.

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

Weak snow (facets and depth hoar) in the lower layers of the snowpack continues to be a concern in our advisory area. Today avalanches occurring in the upper layers have the potential to step down and release the entire snowpack in some places. If this does happen the volume will be large and could run long distances.

Travel in avalanche terrain is not recommended today including being in the runout of a steep slope, like in the flats below Seattle Ridge.

Question of the day: When will we reach the tipping point to activate these weak layers at the base of the snowpack?

Weather

Mon, February 13th, 2017

Yesterday started out with clear skies in the early morning. Clouds moved in and precipitation started early afternoon. Snowfall and winds picked up around 2 pm with over a foot of snow falling overnight. Easterly (SE-NE) winds averaged in the 40s and 50s with gusts into the 90s. Temperatures dramatically rose throughout the day starting around 0F or single digits in the morning and rising to the high 20Fs to low 30Fs by late afternoon.

The storm continues today with another 5-15″ of snow forecasted at upper elevations. Winds will continue to be easterly 20-40 mph with gusts into the 60s. Temperatures will be in the 30Fs in the valleys and the high 20s at ridgetops. The mixing of cold and warm air with the system is causing some uncertainty about the precipitation type and amount. Rain/snowline is hard to determine. There may be rain up to 2000′ or higher or the cold air could stay in place and keep most of the precipitation snow. If you want to read more about it check out the NWS discussion this morning HERE.

The unsettled weather continues as another a wave of moisture is supposed to impact the area tonight into tomorrow. An additional 1-2′ of snow is forecasted but the temperatures and timing are still uncertain. Stay tuned and think cold thoughts…

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	25	9	1	66
Summit Lake (1400′)	22	2	.4	25
Alyeska Mid (1700′)	23	14	1	62

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	12	ENE	40	93
Seattle Ridge (2400′)	14	SE	25	59

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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