Tue, February 19, 2013 Turnagain Pass Avalanche Forecast

Tue, February 19th, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

1 - Low

Below Treeline

Below 1,000'

1 - Low

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

Wind Slabs

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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

For anyone stricken with Powder Fever – President’s Day was just what the doctor ordered. It was one of those great days to enjoy the backcountry. The only avalanche activity seen/reported in the Turnagain area was confined to loose snow sluffs and very small and manageable wind slabs. However, outside of the Turnagain area there was one significant avalanche in the Carter Lake region south of Summit Lake toward Seward. This is outside of our forecasting zone but in our neck of the woods nonetheless. Alex Mclain, Summit Lake’s CNFAIC forecaster, will try to get a closer look this afternoon.

Today, fresh wind slabs will be our main concern as the east winds ramp up. There is a plethora of loose snow out there to be blown into soft and sensitive slabs. These should be easy to identify by watching where the wind is blowing and visibly loading slopes. Cracking in the snow around you will likely be your next clue. Wind patterns get pretty complex around Turnagain but suspect areas are upper elevation ridgelines and over rollovers on south, west and northerly aspects.

Loose snow avalanches in areas out of the wind will be an additional concern. With the decrease in temperature overnight, these could run further and faster than they did yesterday. This issue pertains to below treeline elevations as well.

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

There remain two layers buried below the surface we still have our minds on:

First, a thin layer of weak snow that sits on a late January crust. This is now buried 2-6’ deep and we have not seen avalanche activity within this layer in the Turnagain region. This has been more of an issue in the Girdwood Valley where avalanche activity has been seen and possibly in other surrounding locations (i.e., Placer Valley and 20-mile).

Second, the weak snow near the ground from our early season. This is the deep slab problem we have not been talking about much lately. It has gone dormant for now in the Turnagain and Girdwood areas, but we are concerned with the possibility of it coming back to life with a large multi-day storm cycle and/or in the spring. However, in shallower snow pack areas, such as Summit Lake, it is still more up front in our minds. It looks as though the Carter Lake avalanche mentioned above broke in the weak snow near the ground. Hopefully we will get more information on this today.

Weather

Tue, February 19th, 2013

Once again our break between storms is short lived. Yesterday’s mostly clear skies, light northerly winds and temps in the teens are being replaced by another system headed this way. Winds have already shifted to the east overnight but are still light (~10mph). These will pick up through the day into the 20-40mph range. Temperature is on rise at the ridgetops, going from the single digits to the mid-teens. An inversion has set in at the lower elevations where temps are hovering around 10F. Clouds may hold back enough for good visibility for the first part of the day but look to fill the skies by this afternoon.

Tonight and into tomorrow another quick hitting system will move through. It looks as though we will pick up another 6-12 € with snow to sea level and strong east winds on the ridgelines. Stay tuned.

Kevin will issue the next advisory tomorrow morning, February 20^th.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
05/13/24	Turnagain	Observation: Eddie’s, Sunburst, Seattle, Cornbiscuit, Pete’s South	H Thamm
05/13/24	Turnagain	Observation: Turnagain Pass non-motorized side	Amy Holman
05/12/24	Turnagain	Observation: Warm up Bowl	Tony Naciuk
05/07/24	Turnagain	Observation: Turnagain Pass Wet Slabs	A S
04/29/24	Turnagain	Avalanche: Turnagain aerial obs	Tully Hamer
04/27/24	Turnagain	Observation: Johnson Pass	Noah Mery
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

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