Sat, March 15, 2014 Turnagain Pass Avalanche Forecast

Sat, March 15th, 2014

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

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

It’s been snowing – a lot! Anchorage got a significant dump last night. That snow extended to Girdwood and beyond. This is the kind of maritime storm pattern that we are famous for, and we’ve been missing during this drought winter.

The storm snow problem is least stable during the active part of the storm, and tends to stabilize quickly over time. The big message today is that we got a LOT of snow and it will need time to settle out, bond, and stabilize. We are still within the 24 hour window since active storming, and still within the window of high probability to trigger avalanches in the new storm layers.

Storms also create wind slabs and build cornices. Cornices are likely to be bigger and less stable than they were last weeekend.

Time will make these storm layers stable, but today is not the day to test them in big and dangerous terrain.

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

Underneath all the fresh snow from the last 5 days is the prominent crust layer that formed in February. Just above this crust is a weak layer of faceted snow mixed with buried surface hoar.

We did some snow pit testing yesterday. Results indicated the most concerning weak layer (above the Feb. crust) is difficult to initiate, but propagation potential is high. The triggering is difficult because our slab layer (40-50 inches of new snow) is thick and strong. This information tells us that avalanches may be difficult to trigger, but when they do the resulting avalanche can be large and deep.

This kind of deep slab problem is most likely to be triggered from an area of shallower snow. Wind loading patterns during the storm caused scoured ridges which quickly transition to deeply loaded slopes on the downwind side. A skier or snowmachiner is more likely to trigger this problem near the scoured ridge than far into the deep pocket. Once initiated, it could propagate across into the deeper snow.

Larger triggers are also more likely to initiate the deep slab. Snowmachines have the disadvantage here with 600+ pounds of sled and rider weight impacting the slope.

Weather

Sat, March 15th, 2014

This has been a great week for snowfall. Turnagain Pass more than doubled the total snow on the ground from 42 inches on Sunday to 88 inches last night. Total new snow water equivalent is 5.9 inches. Wind during the storm was predominately from the east on Sunburst. Rain did reach up above 1000 feet at times during the storms, but the snow dried out at the tail end of the storm all the way to sea level.

Last night we got a final shot of snow during a cooling temperature trend. This last bit of the storm was widespread from Anchorage to eastern Turnagain Arm.

A chance of snow continues today, with a couple more inches possible. Decreasing clouds through the day may allow the sun to poke through at times. Temperatures should be cooler, in the low 20s. Wind will be light from the south.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
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
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

Riding Areas

The riding areas page has moved. Please click here & update your bookmarks.