Thu, March 26, 2020 Turnagain Pass Avalanche Forecast

Thu, March 26th, 2020

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

Wet Loose
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Terms such as "unlikely", "likely", and "certain" are used to define the scale, with the chance of triggering or observing avalanches increasing as we move up the scale. For our purposes, "Unlikely" means that few avalanches could be triggered in avalanche terrain and natural avalanches are not expected. "Certain" means that humans will be able to trigger avalanches on many slopes, and natural avalanches are expected.

Size of Avalanches

Avalanche size is defined by the largest potential avalanche, or expected range of sizes related to the problem in question. Assigned size is a qualitative estimate based on the destructive classification system and requires specialists to estimate the harm avalanches may cause to hypothetical objects located in the avalanche track (AAA 2016, CAA 2014). Under this schema, "Small" avalanches are not large enough to bury humans and are relatively harmless unless they carry people over cliffs or through trees or rocks. Moving up the scale, avalanches become "Large" enough to bury, injure, or kill people. "Very Large" avalanches may bury or destroy vehicles or houses, and "Historic" avalanches are massive events capable of altering the landscape.

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Yesterday skies were mostly overcast and the temperatures were warm with weather stations recording temperatures above freezing as high as 4000′. Observers in the mid and lower elevations reported saturated snow and some natural wet loose avalanches in the afternoon. The skies have cleared overnight and temperatures have cooled. Expect melt-freeze crusts on surfaces that had wet to moist snow yesterday. In the Alpine northwest winds should generally keep things cool and locked up. What to watch for today is protected lower elevation slopes that receive direct sunshine. Daytime heating and solar radiation could soften the crust, you could sink into the saturated snow below and initiate a wet loose avalanche on a steep slope. If your snowmachine/skis/splitboard starts punching deep into the snowpack, it’s time to choose a different aspect. This is when wet loose avalanches will become possible to trigger. These wet sluffs could start quite small and if conditions are right, they can entrain enough snow to cause a larger avalanche than expected. Steep slopes below rocky areas are most suspect. Watch for small natural roller balls. These are a sign that things are heating up!

Wet saturated surface snow over moist snow at 600′. North end of Turnagain Pass. 3.25.20.

Avalanche Problem 2

Wind Slabs
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

Likelihood of Avalanches

Size of Avalanches

Signal Word	Size (D scale)	Simple Descriptor
Small	1	Unlikely to bury a person
Large	2	Can bury a person
Very Large	3	Can destroy a house
Historic	4 & 5	Can destroy part or all of a village

More info at Avalanche.org

Outflow (northwest) winds are in the forecast again today. There is not much snow available for transport at this point. However, it is still a good idea to be on the lookout for any blowing snow and watch for lingering stiff wind slabs on steep slopes in the Alpine. These are from the strong winds on Sunday and Monday. These slabs could be sitting on buried surface hoar may still be possible to trigger. Watch for cracking, hard snow over soft snow or spots that sound or feel hollow.

Additional Concern

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 shallow snowpack zones, triggering a larger slab that breaks in weak snow in the mid and base of the snowpack is still a concern. This is at the higher elevations where drier snow exists. The recent warm weather is changing the character of the slab on top, which can increase the chance a person can initiate a failure in the weak facets below and create an avalanche. Areas with a shallow snowpack are on the south end of Turnagain Pass to Summit Lake. This zone also could be more impacted by outflow winds today, watch for wind loading with the caveat that there isn’t very much snow available for transport.

Weather

Thu, March 26th, 2020

Yesterday: Overcast skies with some pockets of sun poking through. Temperatures in the high mid 30°Fs to mid 40°Fs. Winds were mostly light and southwesterly. Overnight skies were partly cloudy becoming mostly clear. Temperatures were in the mid 30°Fs to mid 20°FS. Winds were light and shifted to the northwest.

Today: Skies are forecast to be mostly clear with temperatures in the mid 20°Fs to high 30°Fs. Winds will be northwesterly picking up mid morning, blowing 10-20 mph with gusts into the 30s. Clouds will move in overnight and temperatures will be in the 20°Fs. Winds will be northwesterly 5-10 mph with gusts into the 20s.

Tomorrow: Mostly cloudy skies with a chance of snow showers and northwest winds 5-10 mph becoming calm in the afternoon. Temperatures will be in the mid 20°Fs to low 30°Fs. Overnight snow showers temperatures in the 20°Fs and east winds 5-15 mph. Looking ahead to the weekend the pattern remains unsettled with snow showers and cooler temperatures.

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

	Temp Avg (F)	Snow Depth (in)
Center Ridge (1880′)	37	64
Summit Lake (1400′)	36	29
Alyeska Mid (1700′)	35	72

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	29	W	8	27
Seattle Ridge (2400′)	32	VAR	3	12

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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