Wed, February 19, 2014 Turnagain Pass Avalanche Forecast

Wed, February 19th, 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

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

We have received a plethora of snowpack and avalanche observations from the skier side of Turnagain pass over the last several days thanks in part to the Alaska Avalanche School hosting a couple different courses in the Turnagain region over the weekend. A common theme since Saturday has been parties remotely triggering avalanches that are failing on a thin layer of facets above the January rain crust. This persistent weak layer seems to be most evident at elevations greater than about 2500’.

With a moderate load of new snow overnight and forecasted through today, this known weak layer will move closer to its tipping point. Terrain (such as the backside of Seattle ridge, snowmachiner side) that has not seen much traffic this season warrants extra caution today as the weak snow in these areas has not been tested by skiers or snowmachiners like it has in areas such as Tin Can and Sunburst. Slopes greater than 35 degrees deserve a wide berth when travelling on or underneath, specifically for the possibility of remotely triggering an avalanche.

For sledders, there is a lot of fun to be had in the flats without exposing your party to avalanche terrain today.

Avalanche Problem 2

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

Snowfall amounts varied significantly during the last 24 hours across our zone with Girdwood picking up 12-16 inches, Turnagain pass picking up 1-2 inches and for comparison Anchorage accumulated about 6 inches. The lion’s share of this snow fell during a short but intense period yesterday evening and through the early morning hours though totals fell well short of the forecasted storm.

Storm slab avalanches will be of increased concern in areas that have seen favorable accumulation, spanning all elevations today. Included in this will be the possibility to trigger a wind slab on leeward slopes or cross-loaded gullies, as there is ample snow available for transport to build tender wind slabs. Though Turnagain saw less snow than other zones overnight, that area has been favored over the last several days of storms (since Friday).

Furthermore, loose snow avalanches are likely today in steep terrain above 35 degrees. Though usually a manageable problem, loose snow avalanches prove most hazardous when initiated above a terrain trap.

Additional Concern

Cornice

Cornice

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

More info at Avalanche.org

Cornices are growing quite large as of late. These “backcountry bombs” not only have a tendency to break much further back on a ridge than one expects but also have a great potential to initiate an avalanche on the slope below. Do not test your luck with cornices today (or ever for that matter!), as a fortunate outcome is highly unlikely.

*Note: The AKDOT webcam is working again on Turnagain Pass! Keep tabs on snowfall as well as the road conditions with this link.

Weather

Wed, February 19th, 2014

Though yesterday’s winter storm warning was canceled mid-day and we didn’t quite see forecasted snowfall amounts, there was a brief and intense burst of snowfall from about 5PM last night to 2AM this morning. Areas north of Turnagain pass including Whittier, Portage, Girdwood and Anchorage all woke up to measurable snowfall.

Yesterday in the core advisory area (Turnagain Pass), temperatures reached the mid to high 20’s with winds peaking around noon in the mid-20mph range. Skies were broken all day during the daylight hours with no snow accumulating during the day.

Today we can expect slightly cooler temperatures in the low to mid-20’s with light winds out of the south east. 2-4 inches of snow is expected throughout the day before tapering off into the overnight hours. Tomorrow looks to be the best chance for some sunny skies before we return to what appears to be an active weather pattern for the weekend.

Observations

Recent Observations for Turnagain Pass

Date	Region	Location	Observer
10/27/24	Turnagain	Observation: Tincan	Michael Kerst
10/21/24	Turnagain	Observation: Turnagain Pass Road Observation	Trevor Clayton
10/19/24	Turnagain	Observation: Tincan – Below Todds Run	Andy Moderow
10/18/24	Turnagain	Observation: Taylor Pass	Eli Neuffer
10/15/24	Turnagain	Observation: Tincan Common	John Sykes Forecaster
10/14/24	Turnagain	Avalanche: Tincan	CNFAC Staff
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

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