Sun, November 20, 2016 Turnagain Pass Avalanche Forecast

Sun, November 20th, 2016

Alpine

Above 2,500'

3 - Considerable

Treeline

1,000'-2,500'

2 - Moderate

Below Treeline

Below 1,000'

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

What a weekend to begin the forecast season here at the CNFAIC. During the last two days we have had over 10 human triggered avalanches. One of these was on a popular low angled slope (Manitoba) in the Summit Lake area. Luckily, from what we know of, no one has been injured in any of these slides. A lost ski and pole on Friday from an individual caught and carried in Tincan Common Bowl seems to be the worst of it so far. With this, we have had 10 public observations in the last two days describing the events and details – thank you for making time to send us your information !!

The problem with the snowpack is a layer of buried surface hoar that sits below new snow from last Thursday. Areas on the North side of the Pass (Tincan and Eddies) saw 10-12″, while the Southern side (Sunburst and over to Summit Lake) saw 5-8+”, hence this buried surface hoar is anywhere from 5-12″ below the surface and is the thickness of slabs folks are triggering. Slabs are soft and releasing while people are riding them as well as being triggered remotely from above or the side.

Two notable characteristics of this avalanche problem:
1- Releasing on very low slope angles, angles in the 20’s (one was measured at 18 degrees!).
2- Running much further than expected

If you are headed out today, be very wary of any slope near treeline or above treeline that has not avalanched. Keep slope angles low and be aware of crossing under slopes above you. If the light gets poor (new snow and wind are expected tonight), be aware of your return route – as not to get suckered somewhere you don’t want to go. Today is another day to be extra conservative – we have a long and hopefully snowy season ahead.

Photo below: Human triggered soft slab avalanches on Sunburst.

Photo below: Human triggered avalanche just above treeline on Tincan. Note the debris that ran over the skin track. More on this report HERE.

Again, thank you to the many people submitting observations – if you haven’t done so already, take a few minutes and check them out.

Weather

Sun, November 20th, 2016

Partly cloudy skies yesterday gave way to some sunshine later in the day with valley fog up to 1,500′. There was no precipitation and temperatures were in the mid 20’s F. Winds were light and variable. Overnight, a trace to an inch of new snow fell at Turnagain Pass.

Today, Sunday, a short lived storm system will move in from the East. Skies are expected to become mostly cloudy by the end of the day with light snow beginning to fall. Ridgetop winds will be Easterly around 10mph and picking up tonight into the 25-35mph range. Overnight, we could see anywhere from 4-8″ of new snow. Temperatures will be in the 20’s F and it looks like snow should fall to sea level again – so cross your fingers!

On Monday, snowfall and wind are expected to tapper off by mid-day and temperatures cool slightly. It looks like we will have a break in weather Tuesday and into Wednesday with temperatures staying in the low 30’s at sea level and the mid 20’s in the mountains.

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

	Temp Avg (F)	Snow (in)	Water (in)	Snow Depth (in)
Center Ridge (1880′)	23	1	0.1	18
Summit Lake (1400′)	21	0	0	3
Alyeska Mid (1700′)	23	0	0	3

RIDGETOP 24-hour data (6am – 6am)

	Temp Avg (F)	Wind Dir	Wind Avg (mph)	Wind Gust (mph)
Sunburst (3812′)	19	East	5	18
Seattle Ridge (2400′)	21	N/A (sensor rimed)	N/A (sensor rimed)	N/A (sensor rimed)

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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