Avy Hazard and Decision Making (from Cement Basin post)

EDIT by Marcus -- this is a split off topic from the Cement Basin post here .

**************

Nice images, nice day, nice terrain, nice snow......but am I missing something here?  Leeward slope, over a foot of wind transported snow, rotten, breakable crust beneath the wind transported, and short slopes yo yo'd in what appears to be a 25 to 35 degree range.  And then a pit dug (before or after making the 'to ski it' decision?), at 35 degrees, with a CT 7, maybe Q1 quality. With some sun,  perhaps some warming, snow settling, soft slab forming if not already a bit wind compacted?  Safe travel practice employed? - hard to tell from picture angles.

The point is, are my friend (who alerted me to the post) and I the only two of the 670 readers of this post, who up to this time have read this post and  wondered a bit about the decision making process leading to this story?   No one else has posted wondering.   I hope not.  It is probably perfectly explainable, I just don't have all the info.       Just thinking.   Gerry

Hi Gerry,

I'm happy to provide some additional info. I probably should've provided some more details from the get-go so that folks would have a better idea of what we were skiing and our decision process...

I did the tap test on a column after our first lap. On our first lap we stuck to very mellow terrain...most of the terrain was less than 25 degrees... the only real exception being that I was actually looking for something steeper so I could do some kind of test, and mid-way through our first lap, when the other skiers were in a safe spot, I did ski cut and stomp a couple very short 35 degree rolls to see if I could get the new snow to move...I didn't get any whoomps, shooting cracks, just a little sluffing.

Before we started our first run, and on our skin up through Bullion, we poked around and looked at the snowpack, and I dug a few hasty pits but because we weren't near a steep pitch, any kind of tap test info would've been skewed (at least thats been my experience in the past trying to assign a tap failure number to a slope that has a rather shallow angle). We figured given what we'd seen from the snowpack on the way up, and what we saw at the top of our first run, it was perfectly reasonably to ski something way less than prime angle and take a closer look at the snowpack when we found something steeper.

I had to veer out of our skin track which was set on a fairly mellow pitch to find a short 35 degree roll to dig the pit on so that we could get a more accurate read on how the crust and new snow was behaving. Given what we found, we continued lapping the mellower pitches we had already skied and deliberately avoided moving into some lines that had a continuous steep pitch.

As for the sun....it was dumb luck that we started our first lap and I snapped some pics right when the sun came out...my guess is that we had sunshine for about 20 minutes before it was overcast the rest of the day. The sun didn't make any obvious changes to the snow we were skiing (it certainly might've effected it some, but not that we could tell)...the snow was still rather light on our second lap when the sky was overcast.

Though the sun was certainly on my mind, and if we had been on a direct south exposure (we were on an east facing slope), its certainly possible that the brief shot of sun we got would've been enough to cause the new snow to become more cohesive and have some slabby instead of sluffy behavior.

Hopefully that helps clear things up. If you think we were behaving recklessly, I'm always welcome to hear constructive criticism.

I think biggest surprise for me for the day was seeing so many tracks down the hourglass - hard crust with 8-10" of wind effected snow on a 35-40 degree lee slope that has a history of avy accidents. With such undulating terrain into the narrow portion of the run, we assumed a pit to be pretty worthless since so many aspects are touched on the way down. We did the mellower slope to skiers left and did not see any cracking, but from the poor bonding we saw on the south side of east peak skinning up (skinning above the skin track caused 8" slab to brake loose in multiple areas), we avoided the hourglass.... I guess things were bonded better than we thought!

I was very surprised at the moderate danger predicted by NWAC too - there was lots of wind transport & loading after it stopped raining.

Thanks so much, Pete, and to your crew.  I hope everyone can revisit both your original and your recent update post, because together they paint the kind of picture we all want to emulate. 

Maintaining good group communications, having your antenna up and being observant your entire trip, maintaining individual and group consciousness, having a plan, sticking to it while choosing the right terrain, safely testing the snowpack, all are so critical to staying safe while still getting the goods. 

I don't hold myself up as an expert to judge others, but have and am investing a lot of time in avalanche education - as both a student and instructor.  And am sometimes outspoken in my opinions.  I think those of us fortunate enough to have gained a lot of avalanche experience, and education, have a responsibility to those at the beginning of their backcountry experiences, to share our knowledge - as others did  for us.  And it was in that spirit that I offered up my comments. Sometimes taking a few extra sentences of explanation can dispel that ski film bravado of just jumping into it and letting it rip, when in fact those ski stars have their heli hovering just out of camera sight and a crew of avy rescue professionals & first aiders on standbye  - just in case.  So I'd say your turns were very well earned.  Thanks!  Gerry

Well, if we're going to analyze the avy hazard and decision-making here, might as well link to the available forecasts and data for reference:

Danger rose for all zones near and west of the Cascade crest:
http://www.nwac.us/dangerrose/preview/2043/

NWAC avy forecast from Sunday, Dec 25, the latest available before this trip: www.nwac.us/archive/sabsea_2011-12-25-1115.html

The updated avy forecast on Dec 26 did not increase the hazard rating either, the key statement perhaps being that "no avalanches were reported upon control work at Stevens Pass or Crystal Mountain Monday morning": www.nwac.us/archive/sabsea_2011-12-26-1236.html

Weather summary: On Dec 25, the Crystal Mountain area had unexpectedly received the most snowfall of any location in the Cascades, with 9" new reported by the ski area and 7" new showing on the Green Valley NWAC telemetry -- no other measurement site had more than 5-6" new that day, with most closer to 2" new. The new snow at Crystal had fallen from 11am to 8pm during moderately strong W and NW winds, see telemetry below. Field reports verified that 9" new snow amount on flat protected slopes, such as in Bullion Basin.

[hr]
I skied several runs on the same slopes and other neighboring slopes with another group that day, and thought that the avalanche danger was Low-to-Moderate at most. It was certainly not Considerable (meaning "Natural avalanches possible; human-triggered avalanches likely.") in any location or aspect that we skinned or skied. Natural avalanches did not appear to be possible, and human-triggered avalanches appeared to be very unlikely.

I think the reason for the relatively low-ish hazard was that the deeper areas of new snow (wherever the wind had transported the snow) felt generally cohesionless, not slabby, and the only slightly slabby areas were the wind-hammered slopes which had much less new snow atop the crust. There's not much avy hazard when the so-called slabs are 2-4" deep maximum, and have no fracture energy or propagation whatsoever. Not sure about where someone saw those 8" slabs beside the skin track up the SW side of East Peak -- we skinned up the same skin track and saw only 2-4" deep mini-slabs (like 1 ski-length in size) beside the skin track in a couple spots, even those only on the iciest sections of smooth old sun crust.

We started the day by breaking trail into Bullion Basin and up Point 6479 (Bullion Peak ?) via its N face and NW ridge. Conditions felt totally stable underfoot while putting in the skin track, even on every steep roll on the open face and ridge, nothing was slabby or sliding. We skied down the N face (an obvious big avy slope) in very stable conditions. Slight slabbiness right near the summit where the new snow was wind-hammered and thin (0-4"), but that was just a breakable windcrust that was not sliding anywhere. Then again cohesionless and not slabby or wind-affected at all just a bit lower as soon as the snow got deep enough (say 6-8") to be fun skiing.

When the sun came out at the end of that run (around 11:30am), we decided to head up the SW side of East Peak just to get out of the very cold shade and enjoy the sunshine. We were just planning to ski the SW side, but decided to ski the steeper NE and ENE aspects (30-40 degrees) from the summit of East Peak only after seeing a handful of ski tracks having already descended safely down this aspect (another obvious big avy slope). We found excellent stable powder with absolutely nothing sliding or moving, and quite deep, generally 9-12" deep all the way down to the flats at 5900 ft. Nice enough to ski 2 runs down there. We dug no pits.

Regarding sun and warming: at this time of year, the sun can really only affect steep S-facing slopes due to its very low angle and limited range of azimuth. All other aspects and slope angles get very minimal insolation even on a totally sunny day -- they are almost immune. Despite the sun being out for a while this day (full sun for maybe 20-30 minutes, partial filtered sun for maybe 2-3 hours), even the steep S and SW facing slope from the summit of East Peak showed almost no signs of sun effect. When we finally skied back down at sunset, there was no breakable sun crust, just very nice stable powder once we dropped below the thin wind-hammered areas up high. So other slopes (everything not steep S-facing) obviously had zero sun effect this day. There was very little warming during the day, and the next incoming storm did not arrive until late afternoon, with very light snowfall beginning near 4pm (too light to show up on telemetry).

Some photos of our day:

N aspect:


SW aspect:


ENE aspect:





[size=small][tt]
Northwest Weather and Avalanche Center                                                    Northwest Weather and Avalanche Center
Crystal Mountain Ski Area, Washington                                                     Green Valley, Crystal Mountain Ski Area
                                                                                         
MM/DD  Hour  Temp  Temp    RH    RH  Wind  Wind  Wind  Wind  Hour Total 24 Hr Total       MM/DD  Hour  Temp 24 Hr Total
         PST     F     F     %     %   Min   Avg   Max   Dir Prec. Prec.  Snow  Snow               PST     F  Snow  Snow
             6830' 4570' 6830' 4570' 6830' 6830' 6830' 6830' 4570' 4570' 4570' 4570'                   6230' 6230' 6230'

---

     

---

12 25   500    35    43    44    47    10    24    44   200     0     0     0    32       12 25   500    35     0    43
12 25   600    34    44    50    41    14    28    56   228     0     0     0    32       12 25   600    34     0    43
12 25   700    32    41    53    46    13    30    53   191     0     0     0    33       12 25   700    32     0    42
12 25   800    31    42    55    41    13    34    59   190     0     0     0    33       12 25   800    32     0    42
12 25   900    30    42    52    39    13    35    63   210     0     0     0    33       12 25   900    31     0    42
12 25  1000    29    41    54    39    15    34    65   212     0     0     0    33       12 25  1000    29     0    42
12 25  1100    24    33    99    95    11    29    64   206   .03   .03     0    31       12 25  1100    24     0    37
12 25  1200    24    32    99    96    13    31    55   234   .08   .11     1    33       12 25  1200    24     0    43
12 25  1300    24    32    98    97     8    21    44   287   .05   .16    47    33       12 25  1300    23     1    43
12 25  1400    24    31    99    97     4    14    30   272   .03   .19    47    33       12 25  1400    23     1    43
12 25  1500    22    30    99    99     7    21    52   215   .11    .3     3    35       12 25  1500    22     3    45
12 25  1600    21    29    98    99    11    29    53   263   .07   .37    47   238       12 25  1600    20     4    44
12 25  1700    20    28    98    99    10    28    56   274   .09   .46     4    37       12 25  1700    19     5    47
12 25  1800    18    26    97    99    11    28    50   190   .09   .55     5    39       12 25  1800    17     7    50
12 25  1900    18    26    97    98    11    26    48   262   .04   .59     5    38       12 25  1900    16     7    49
12 25  2000    17    26    97    98     7    22    42   268   .02   .61     5    38       12 25  2000    16     7    48
12 25  2100    16    25    96    97    13    21    30   291     0   .61     5    38       12 25  2100    15     8    51
12 25  2200    15    23    96    97     7    16    25   308     0   .61     5    38       12 25  2200    14     7    51
12 25  2300    16    22    96    97     8    17    28   278     0   .61     5    37       12 25  2300    13     7    51
12 26     0    16    22    96    96     5    15    26   276     0   .61     5    37       12 26     0    13     7    50
12 26   100    14    21    96    97     6    18    27   273     0   .61     5    37       12 26   100    12     7    50
12 26   200    15    21    96    96    10    21    30   289     0   .61     5    37       12 26   200    12     7    51
12 26   300    15    20    96    95     8    14    23   270     0   .61     5    38       12 26   300    12     7    50
12 26   400    15    20    96    96     6    11    16   164     0   .61     5    38       12 26   400    12     7    49

---

     

---

12 26   500    15    21    97    97     3     9    20   242     0     0     5    38       12 26   500    14     7    50
12 26   600    16    23    97    97     4    11    19   203     0     0     5    38       12 26   600    15     7    50
12 26   700    18    24    94    97     4     9    14   206     0     0     5    38       12 26   700    15     7    50
12 26   800    19    25    96    97     1     7    14   142     0     0     0    38       12 26   800    18     7    50
12 26   900    20    25    95    96     4    12    22   151     0     0     0    38       12 26   900    17     7    50
12 26  1000    20    25    90    94     7    21    37   189     0     0     0    38       12 26  1000    18     7    50
12 26  1100    22    27    72    90    18    30    42   184     0     0     0    38       12 26  1100    20     7    49
12 26  1200    22    27    72    94     6    18    40   150     0     0     0    38       12 26  1200    22     7    49
12 26  1300    21    29    62    87     3    15    33   194     0     0     0    38       12 26  1300    22     7    48
12 26  1400    21    28    68    86     3    18    37   204     0     0     0    37       12 26  1400    21     7    49
12 26  1500    21    28    85    94     2     8    22   164     0     0     0    37       12 26  1500    19     6    49
12 26  1600    20    27    90    95     0     4    12   194     0     0     0    38       12 26  1600    18     6    49
12 26  1700    18    26    95    91     4    11    20   198     0     0     0    38       12 26  1700    17     6    49
12 26  1800    18    26    95    93     6    19    37   207     0     0     0    38       12 26  1800    19     6    49
[/tt][/size]

Amar, I love the last photo with a great "face shot" .