Mon, April 08, 2013 Turnagain Pass Avalanche Forecast

Mon, April 8th, 2013

Alpine

Above 2,500'

2 - Moderate

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

2 - Moderate

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 looks as though winter is back. We have a cold storm moving in this morning that will bring another round of snow all the way down to sea level. Snowfall is just getting going now and is expected to drop ~6″ on the Pass during the day with possibly up to 10″ in favored locations. Winds associated are not too exciting – light from the east with moderate gusts. That said, new snow with some wind will spice up the avalanche conditions. Snow amounts are modest however, so most of the avalanche activity should be low volume – the exception will be areas the wind is depositing snow into deeper drifts and slabs.

There are three main questions to keep in mind if heading out today:
1- How much snow is accumulating in the area you are traveling? The more snow, the bigger the avalanche.
2- Is the wind blowing and loading slopes? Only 6″ of new snow with moderate wind can build sensitive wind slabs over a foot deep (see yesterday’s activity below). These could quickly through you down a slope and into an unmanageable situation.
3- How well is the new snow bonding with the variety of underlying surfaces? Slick crusts on southerly aspects will have a hard time holding snow. Northerly aspects have a mix of soft snow, wind affected surfaces and potentially buried surface hoar. I’m expecting bonding on northerlies to be poor in some areas and fairly good in others.

Other than wind slabs mentioned above, we can expect loose snow avalanches in steep terrain to release both naturally or by a person. Also, shallow storm slab avalanches on slopes greater than 35 degrees are possible due to warming temperatures during snowfall.

Yesterday’s avalanche activity:
Folks were able to find and trigger fresh wind slabs 6-12″ deep yesterday on upper elevation northerly slopes. This seemed to be confined to the southern end of the Pass where 4-8″ of low density snow fell Saturday evening (only 2-4″ fell on the northern side of the Pass). Southerly winds blew during the snowfall and then kicked up again mid-day yesterday continuing to load northerly slopes. We saw a few natural loose snow avalanches in the Lynx Creek area as well – see Fitz’s video HERE.

Weather

Mon, April 8th, 2013

During the past 24 hours we have seen partly cloudy skies with a trace of snowfall. Ridgetop temperatures reached 20F yesterday before dropping to the single digits overnight. Winds were mainly out of the east averaging 8mph with gusts up to 25mph.

Today we have another, and more developed, system moving in from the Gulf. Turnagain Pass will likely see snow amounts similar to Anchorage (this is a good set up for Anchorage). We should see around 6-10″ through the day with warming temperatures. Ridgetop winds are expected to be light from the east with gusts to 25mph. Temperatures should rise to the upper-teens on the ridgetops and to the upper 20’s at 1,000′ before they cool off again as the flow switches to the north tonight.

Tuesday, colder air moves in from the northwest as the low pressure wraps around southcentral. This could give us several more inches of light snow – and if things set up right, possibly more. Stay tuned.

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I will issue the next advisory tomorrow morning, April 9th.

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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