Fri, December 25, 2015 Turnagain Pass Avalanche Forecast

Fri, December 25th, 2015

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

A winter storm warning is in effect for the region today. If the forecasted snow totals verify we could quickly start to have storm snow concerns. Initially we could see loose snow avalanches. The new snow will land on weak snow. Surface hoar and near surface facets have formed during the past few days on all aspects and elevations. These could become a very reactive weak layer as the new snow piles up. Winds have destroyed the surface hoar in some areas in the Alpine but unfortunately we will not have x-ray vision to determine exact distribution. The winds have already started to pick up this morning. This combined with the new snow could rapidly create sensitive slabs. Pay close attention to changing conditions. Watch for heavy precipitation intensity, strong winds, shooting cracks and whumpfing. Low visibility will make it hard to see what is above you. Avoid travel in runout zones. If you do venture out today conservative terrain choices are advised.

Yesterday’s snow surface = Today’s weak layer.

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

The weak snow that formed in early December sitting over the Thanksgiving Rain Crust or old hard snow is now buried under 2-4′ of snow. This combination has been the cause for concern and heightened caution in the backcountry for the past week. This setup could now become overloaded with the additional weight of new snow and wind loading. If avalanches step down into this layer, they could be quite large and destructive.

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

There have been cornice triggered avalanches during the past week and there are looming sections overhanging slopes today. Cornices will grow quickly with the new snow and may be triggered by the increasing winds. Visibility may make it challenging to see what is above. This is an added reason to stay away from runout zones.

Weather

Fri, December 25th, 2015

Yesterday was clear in the morning with increasing clouds throughout the day. Winds were light and shifted from W to E. Temperatures were in the single digits in the valleys and the mid-teens at ridge tops.

The winds have picked up this morning and temperatures are warming as the weather system approaches.

NWS Zone Forecast for Turnagain:

…WINTER STORM WARNING FOR HEAVY SNOW REMAINS IN EFFECT FROM
9 AM THIS MORNING TO 6 AM AKST SATURDAY…

* SNOW…13 TO 26 INCHES…HIGHEST AMOUNTS THROUGH TURNAGAIN PASS AND
NEAR GIRDWOOD.

* VISIBILITY…NEAR ZERO AT TIMES IN HEAVY SNOW AND BLOWING SNOW.

* WIND…EAST WIND 10 TO 25 MPH EXCEPT EAST 40 TO 55 MPH THROUGH
PORTAGE VALLEY AND TURNAGAIN ARM…STRONGEST WINDS THIS
EVENING.

* TIMING…SNOW WILL DEVELOP THIS MORNING THEN BECOME HEAVY THIS
AFTERNOON. HEAVY SNOW WILL CONTINUE THROUGH TONIGHT FOR INLAND
AREAS BEFORE DIMINISHING EARLY SATURDAY MORNING. LOCATIONS ALONG
THE COAST WILL CHANGE TO RAIN LATE THIS AFTERNOON OR EVENING
RESULTING IN LESS SNOW ACCUMULATION OVERALL. The rain/snow line is expected to rise to 500′ tonight.

The storm continues into tomorrow with snow/rain showers and easterly winds. Temperatures will be in the high 20Fs to mid 30Fs.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	15	0	0	49
Summit Lake (1400′)	10	0	0	17
Alyeska Mid (1700′)	15	0	0	35

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	14	ESE	8	15
Seattle Ridge (2400′)	14	ESE	10	14

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

Riding Areas

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