Fri, March 22, 2019 Turnagain Pass Avalanche Forecast

Fri, March 22nd, 2019

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

Wet Slab
Certain

Very Likely

Likely

Possible

Unlikely

Likelihood
Historic (D4-5)

Very Large (D3)

Large (D2)

Small (D1)

Size

Wet Slab

Wet Slab avalanches are the release of a cohesive layer of snow (a slab) that is generally moist or wet when the flow of liquid water weakens the bond between the slab and the surface below (snow or ground). They often occur during prolonged warming events and/or rain-on-snow events. Wet Slabs can be very unpredictable and destructive.

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

Heavy rain and strong winds will remain the primary weather factors initiating a wet avalanche cycle below 2500’ today. Numerous large and very large wet slab avalanches have been releasing over the last two days and will continue through today. In some areas wet slab avalanches are taking the entire winter snowpack and leaving behind impressive piles of dirty debris. In other places, drier avalanches are releasing in the alpine and taking out the entire avalanche path – like Lipps West face seen yesterday. Many popular slopes are still intact, hanging in balance and may avalanche at any time. Today’s message is simple – stay well away from any avalanche terrain including runout zones! Wet slab avalanches are unpredictable and unsurvivable if someone was to get caught.

Storm Slabs:
Today expect rain/snow line to fluctuate between 2000’ and 2500’. In the alpine, above 2500’ where 2-3+ feet of new snow has fallen over the last few day storm slabs are expected to be unstable. Strong Easterly winds 30-40mph and up to another 1-2’ of snow will be adding stress to the upper elevation snow pack. Natural storms slabs are likely where the snow is dry and could initiate very large avalanche in an older deeper layer of the snowpack.

South of Turnagain in the Summit Lake and areas in the interior Kenai Peninsula have a very poor snow structure with variety of old weak layers (facets and buried surface hoar) in the mid and base of the snowpack. Warm temps and rain have saturated the snowpack below 2000’ and numerous large wet slab and dry slab avalanches have released. Today up to .5” of rain is forecasted below 2500’ in the interior areas of the Kenai and with it more natural avalanche activity.

Natural avalanche on Lipps seen yesterday morning 3/21/19

Many wet slab avalanches have been releasing on Seattle Ridge (SE aspect) over the last few days, but many slopes still remain intact and could release at any time.

Dirty wet debris seen on the SW facing terrain of Goat Mt shoulder in Girdwood Valley. This avalanche released sometime early Thursday morning (3/21/18). Photo courtesy of G. Creighton.

Additional Concern

Glide Avalanches

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.

More info at Avalanche.org

In addition to wet slab avalanches glide cracks have been releasing over the last few days including one on Seattle Ridge and many in Girdwood Valley. Similar to wet slab avalanches these are very unpredictable and impossible to manage and another reason to avoid avalanche terrain today.

New glide avalanche on a South aspect of Goat Mt in Girdwood. Photo courtesy D. Nelson

Weather

Fri, March 22nd, 2019

Yesterday: Skies were overcast and light to heavy rain was observed throughout our region. Easterly winds were strong (30-40mph) increasing into the 50s mph overnight and several gusts in the 100’s at ridgetops. During the day precipitation was heavier near Turnagain Arm, Portage and Girdwood Valley. Overnight intensity increased for a total of 1″ of rain in Turnagain and 1.6″ of rain at Alyeska Midway station in Girdwood. In Portage 2.27″ of rain was recorded near Bear Valley. In the alpine these water totals translate to 1-3′ of new snow. Temperatures have remained in the low-40Fs at sea level, mid-30Fs at 1000′ and rain/snow line has dropped around ~2000′.

Today: Rain will be heavy in the morning and early afternoon with another 0.5″ – 1.5″ or rain is expected today. This is 1-2′ of snow in the alpine. Higher precipitation totals will favor Girdwood, Portage and the North side of Turnagain Pass – more coastal areas. Temperatures at sea level will be in the 40Fs and upper 30Fs at 1000′. Rain/snow line will fluctuate between 2000′ and 2500′ today. Easterly Ridgetop winds will remain strong 30-40mph with gusts in the 50-60s mph.

Tomorrow: Rain is expected through the weekend with lighter rain on Saturday. Coastal areas like Portage Valley will see another dose of heavy rain Saturday evening into Sunday. Temperatures will remain in the 40Fs at sea level and mid to upper 30Fs at 1000′. Rain/snow line will be around 2000′. Ridgetop winds from the East will still be elevated, 20-35 mph through Sunday morning. High pressure is in the forecast for Monday and Tuesday, but very warm above freezing temperatures will continue.

*Seattle Ridge weather station anemometer has been experiencing some issues and may be under reporting wind data.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	36	rain	1.0	76
Summit Lake (1400′)	38	rain	0.3	27
Alyeska Mid (1700′)	36	rain	1.6	70

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	27	ENE	41	103
Seattle Ridge (2400′)	32	*SE	19	75

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

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