Wed, April 03, 2019 Turnagain Pass Avalanche Forecast

Wed, April 3rd, 2019

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

Glide Avalanches
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

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.

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

Glide cracks are scattered throughout the advisory area and have been avalanching daily. Yesterday morning two new glide avalanches were seen in Turnagain Pass on Southwest aspects of Eddies and Corn Biscuit. In the early evening Magnum’s Southwest face had a fresh new glide avalanche. Glide avalanches are full depth avalanches that have the potential to be very dangerous. They are not associated with human triggers and occur spontaneously without warning. Glides can release even if a hard surface crust is present (unlike the wet loose and wet slab avalanche problems). Many glides are releasing in areas where folks are entering/exiting popular terrain. The best way to manage this problem is to identify them and avoid travel under their runout zone. Remember they can release at any time!

New glide avalanche on Magnum’s SW face released yesterday afternoon.

Corn Biscuit (left) has a lot of new glide cracks and a new glide avalanched overnight on Monday. Lipps (right) glide crack has widened significantly in the last two days.

Seattle Ridge has seen a lot of glide avalanches and wet avalanches over the last week and a half. Be aware that glide cracks are still opening up and have the potential to cross the uptrack, like one that released on Saturday.

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

LOOSE WET: Overall the possibility of natural wet loose and wet slab avalanches has decreased over the last two days. The snowpack has seen many days of a springtime melt-freeze pattern and many low to mid elevation terrain has shed (avalanched) a lot snow. In the Alpine, where night time temps have dropped well below freezing, a firm surface crust has formed. Today with daily warming and sunny skies there is still potential for a person, on skis or a machine, to trigger an avalanche in the afternoon/evening on solar aspects. If the snow surface breaks down and becomes wet and punchy, it’s time to get onto shaded slopes or off the one you are on.

CORNICES: Cornices are very large and direct sunshine can make them easier to trigger in the afternoon. Give cornices a wide berth and avoid travel directly below where one might fall.

South of Turnagain in Summit Lake and areas in the interior Kenai Peninsula have a very poor snow structure with variety of old weak layers within the snowpack. This poor structure is most suspect in the alpine above 3000’ – on shaded aspects any time of the day or on steep solar aspects late in the afternoon when surface crusts start breaking down. Triggering a persistent slab 2-3’ deep is becoming less likely with time, but not out of the question. In the mid and lower elevations where a stout crust as formed, monitor surface conditions and adjust your plans if the surface snow is unsupportable on Solar aspects later in the day.

Weather

Wed, April 3rd, 2019

Yesterday: Skies were sunny in the morning with high clouds moving in the afternoon. Temperatures reached the mid 40Fs in the mid and lower elevations. Ridgetop temps reached the mid 30Fs and dropped to the mid 20Fs overnight. Ridgetop winds were 5-15mph from the West. No precipitation fell.

Today: Skies will be partly cloudy to clear. Daytime temperatures are expected to reach the mid 40Fs in the mid and lower elevations. In the alpine daytime temps will be in the 30Fs and overnight will drop into the 20Fs. Winds are expected to be light from the Northwest with some areas seeing moderate NW winds (20s mph) like Turnagain Arm. No precipitation is expected.

Tomorrow: Skies could range from mostly cloudy with broken skies at times. There’s a chance for a few flurries in the alpine, but no accumulation is expected. Winds will shift to an Easterly direction and increase into the 10-20mph range in the afternoon. Saturday looks like our first opportunity for a storm to bring a few inches of snow to the alpine and rain showers to lower elations. Stay tuned!

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	37	0	0	66
Summit Lake (1400′)	36	0	0	21
Alyeska Mid (1700′)	38	0	0	58

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	W	6	18
Seattle Ridge (2400′)	34	WNW	2	10

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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