Thu, March 13, 2014 Turnagain Pass Avalanche Forecast

Thu, March 13th, 2014

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

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

There are 2 interfaces in today’s snowpack that may act as sliding layers. They can be separated out by the 2 storms we’ve seen this week.

Storm snow that started falling last night may slide at the old surface layer we were skiing on yesterday. Yesterday we had a sunny break in the weather that built sun crusts on southerly aspects. With new snow building, this could become a sliding interface.

This morning the new storm snow is less than a foot deep, but is expected to reach closer to 2 feet by the end of the day.

Avalanche Problem 2

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

Monday’s storm fell on the old February crust, which has some buried surface hoar acting as a weak layer above the crust. Yesterday we experienced frequent collapsing (whumphing) on this layer at elevations between 1000 and 2500 feet. Some avalanche activity on Tuesday was reported up to 2 feet deep from this storm.

A worst case scenario today would be avalanches that slide 3-4+ feet deep at the crust interface. This would include snow from both storms this week.

Weather

Thu, March 13th, 2014

The storm that ended Tuesday dropped about 2 feet of snow in Girdwood and Turnagain Pass. That snow transitioned to rain at lower elevations at the end of the storm.

This morning, Center ridge weather station has already recorded about 9 inches of snow and up to 0.8 inches of water equivalent. Sunburst station saw wind gusts to 105mph overnight from the East.

Snow/rain line is predicted to stay at sea level today, but temperatures are right on the threshold. Some rain is possible at sea level. Snow above 1000 feet is expected to reach 11-16 inches today and another 9-14 inches tonight. An east wind will stay strong while this storm continues.

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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