Tue, March 19, 2019 Turnagain Pass Avalanche Forecast

Tue, March 19th, 2019

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

3 - Considerable

Below Treeline

Below 1,000'

3 - Considerable

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
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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 the large natural avalanches kept occurring with notable avalanches observed in Crow Creek, on Tincan, Seattle Ridge, Petes North, Twin Peaks, and through Summit Lake. These had very deep crowns, and were running into the flats in many locations. This was the second day in a row of very large slab avalanches. Today is a break in the barrage of storms after 6 days of HIGH avalanche danger. Temperatures are dropping this morning but are expected to rise again this afternoon and it should be partly sunny today. The natural avalanche activity should decrease but the potential for a very large human triggered slab avalanche remains. The current snowpack needs some time to adjust to all the loading from multiple feet of snow, strong winds and rain. Be patient! We are optimistic that at some point it will stabilize but today is definitely not the day test it out. Choose terrain very wisely. The slabs could be very deep, there may be no signs of instability and it could be the 1st or the 10th skier or snowmachine on the slope that triggers the avalanche. Avalanches could be triggered remotely from thin spots. In addition, pay attention to solar warming and the potential for roller balls and wet loose avalanches on sunny aspects.

Tincan avalanche. Occurred sometime between 12:15-12:25 pm. 3-18-19. Photo: Corey Anderson

Avalanche to the ground on Seattle Ridge, 3-18-19.

Large avalanches, Templeton – Summit Lake, 3-18-19.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Stay away from cornices. They have grown large and could be very tender and dangerous today. Triggering a cornice fall also has the potential to trigger a deep avalanche on the slope below.

Weather

Tue, March 19th, 2019

Yesterday: Mostly cloudy skies and rain/snow showers on and off throughout the day favoring Portage and Girdwood. Temperatures were in the 30Fs and 40Fs. Winds were northeasterly 15-25 mph with gusts into the 50s. Overnight skies became broken and temperatures dropped slightly. Easterly winds decreased blowing in the teens with gusts into the 30s.

Today: Partly sunny skies with temperatures in the 20Fs to high 30Fs. Sea level temperatures will be around 40F. Winds will be easterly 5-15 mph with gusts into the 20s. Clouds move back in tonight and winds pick up early morning Wednesday as the next warm wet storm moves over the region. Snow should start overnight.

Tomorrow: Mostly cloudy with rain and snow showers that could be heavy at times. Rain/snowline is forecasted around 2000′. Easterly winds blowing 20-30 mph gusting into the 50s. The warm wet pattern is forecast to continue into the weekend.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	35	0	0.1	88
Summit Lake (1400′)	37	0	0.1	30
Alyeska Mid (1700′)	34	0	0.46	78

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	25	NE	20	62
Seattle Ridge (2400′)	30	*N/A	*N/A	*N/A

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
04/16/24	Turnagain	Observation: Cornbiscuit	Krueger / Matthys Forecaster
04/15/24	Turnagain	Observation: Taylor Pass	John Sykes Forecaster
04/15/24	Turnagain	Observation: Seward Highway – Tern Lake to Portage	Joel Curtis
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

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