Avalanche Discussion

I'd like to spur periodic discussion regarding the accumulating snow pack in order to educate myself, and maybe others out there.

So far, it looks like there is going to be a 6-10" layer of ice in most places within the PNW. The storm activity to hit this weekend of 12/12-12/14 looks to bring Artic-air, cold temps, and a dumping of super light-weight dry snow.

Any thoughts on the future snow pack as influenced by such a sandwiched light-weight snow build on top of an ice layer??? Possible faceting, perhaps? Will this be a week layer to look out within the coming weeks of the season once we receive an additional 2-3' of snow?

It would be great to have a multiperspective dialogue going on snowpack.

I'll add what I put in a Paradise area report:

Things softened up just a tiny bit as we were leaving on Thursday (12/11). It doesn't look like the existing snow would've had a chance to soften up though due to continued cold temps and wind so most likely this current load is going to slide. Or maybe worse since this new snow has such a low water content it won't sufficiently weight the crust and the whole works will stay stable for a bit longer for more snow to accumulate on top, then once properly loaded it'll go.

Either way, we should see this crust layer on any pit that goes to within 2' of the bed surface with all this current fluff on top.

I'd love to hear others opinions as that's just my thoughts. I'm new to the whole telemetry thing so by all means if I'm way off base please chime in.

www.nwac.us/products/SABSEA

Emphasis added ...

BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON
CASCADES AND MT HOOD AREA
NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON
0830 AM PDT SAT DEC 13 2008

[...]
SATURDAY NIGHT THROUGH SUNDAY NIGHT
Strong east to northeast winds are expected in most
locations late Saturday and Sunday along with bitterly
cold temperatures. While decreasing light showers are
likely in the north with gradually decreasing light to
moderate snow or snow showers in the south, the
increasing and shifting winds combined with very cold
temperatures should still help to produce a further
slight increase in the danger. The danger increase should
be greatest on west to southwest exposure slopes above 5
to 6000 feet where locally considerable danger is
possible on steeper terrain with a smooth underlying
ground surface or on slopes where most anchors have been
buried. Travelers are urged to perform stability tests
before traversing steeper wind loaded terrain, especially
in higher elevation wind loaded terrain, as the cold air
temperatures and associated strong temperature contrasts
in the snowpack should help weaken the bond of recent
snow to the pre-existing snow surface.

A significant danger may also exist from the expected
weather in most areas. The combination of very low air
temperatures and strong winds should produce wind chills
dropping to well below zero. Back country and other
travelers are urged to take precaution to protect exposed
flesh and minimize time exposed to the wind. While some
partial clearing is likely, especially in the north later
Sunday, blowing and drifting of the very low density and
fluffy surface snow should produce reduced visibility and
difficult travel in many areas.

Please also note that the cold air temperatures combined
with the still relatively shallow snowpack should result
in significant faceting and weakening of the overall snow
structure later this weekend and well into next week.
This greatly weakened structure will become a substantial
avalanche concern whenever future more normal and
generally warmer conditions deposit higher density
snowfall over the generally weak and still relatively
shallow Northwest snowpack. The anticipated development
of some surface hoar in wind sheltered areas when skies
begin clearing late Sunday into early next week will only
add to the potential for a rapid avalanche danger
increase when the next significant snowfalls arrive.

How about going to dig a pit on top of Goat Island Mountain? That would be an enjoyable slog.

It would be great to have a multiperspective dialogue going on snowpack.

I'll add what I put in a Paradise area report:

Things softened up just a tiny bit as we were leaving on Thursday (12/11). It doesn't look like the existing snow would've had a chance to soften up though due to continued cold temps and wind so most likely this current load is going to slide.  Or maybe worse since this new snow has such a low water content it won't sufficiently weight the crust and the whole works will stay stable for a bit longer for more snow to accumulate on top, then once properly loaded it'll go.

Either way, we should see this crust layer on any pit that goes to within 2' of the bed surface with all this current fluff on top.

I'd love to hear others opinions as that's just my thoughts. I'm new to the whole telemetry thing so by all means if I'm way off base please chime in.

Great! Thanks for the perspective analysis. That's exactly what I'd like to evoke...

And thanks Lowell for the info.

Tell your partners about this thread and let's keep a continuous dialogue going and keep it on topic throughout the season.

Well at SnoQ Pass this morning, what people yesterday described as "utah like pow" had become a bit more dense with wind packing. I could see alot of snow getting transported. I didn't see faceting or crystals forming yet. The moon this morning was great for pre dawn travel. I think I heard that it is traveling closer to earth lately, unusually bright, and higher tides. There is enough to make light turns and of course there are hazards lurking but the brushed slopes were fun.

How about going to dig a pit on top of Goat Island Mountain? That would be an enjoyable slog.

ROTFLMAO!!!

On a more serious note, Kyle and I voted for some "Utah Pow" off of Three Way peak. Today was not a Utah day though, with obvious wind packing affecting the pack and what was falling. The snow falling (I think due to extremely cold temps and high wind) was very small and granular, and extremely light. With the wind packed snow, we triggered some minor soft slabbage, but depths of propogating cracks were anywhere from 6-12". I'm guessing with additional snow and wind this could become not so minor slabbing.

I just got back from my AIARE Level I at Mt Baker, so I feel like I ought to chime in with my observations. If I'm wrong about anything, correct me, I'm still learning. We dug quite a few pits, but all at lower alititudes (below Artist Point).

Some of the guys who arrived early on Friday triggered a small slab off the North side of Table Mountain. By Sunday the same area was tracked out.

What we saw Saturday was about 1m deep snow, largely unconsolidated. There was an ice crust about two feet down, with a layer of surface hoar on top of that. There was also a discrenable layer a few inches down, with just a slight change in density. Sunday we saw mostly the same, with just a little settling and a few extra inches of light on top. Most notably we saw far more depth facets than we did on Saturday. Not enough to really worry me, but if the trend continues it could get really bad. Wind loading appeared very light, although as we were leaving Sunday the winds picked up and we could see a lot of wind transport on Table.

Overall, we found everything pretty safe, but saw enough to say the area needs monitoring to see how it develops. We also noted the NWAC forecast specifically mentioned areas of instability from 5k to 6k, which we stayed out of.

There was an ice crust about two feet down, with a layer of surface hoar on top of that. 

I understand the lurking dangers of surface hoar, but any additional insight on ice crusts? It seems that new layers wouldn't bond well to a bed of ice, and I'm trying to understand all of this better.

An ice crust makes a great bed surface, but how well the snow above bonds can depend on a great number of factors. An ice crust can even improve stability by "bridging" weight over a larger area. So an ice crust by itself isn't really good or bad...

The snow we saw seemed to be bonded OK to the crust. I'd just call it neutral right now. If you get a slab going, it's probably going to be on that crust though.

The Longmire gate opened at 1137 today and a small convoy traveled to the Paradise parking lot. About 16 or so people headed up towards Alta Vista, most were skiers. By the time the group reached the cut over at Alta Vista to get onto the Glacier Vista rollers only 8, by my count, were left. If you stood in the snow, you would be right in up to your chest. No bottom with your pole in most areas. As the group moved along, 4-6 foot arches would break along the snow on the up hill side any where there was even a modest slope. The group moved up along the high points of the rollers. The winds were very strong, it was very cold and it was still snowing with lots of clouds swirling around. I stopped at the last big rocks before you head over to the bottom of Pan Pt. I saw 2 skiers and then 3 skiers trying to head up along the right side of Pan face just right of the trees. I hung out a while waiting to see if they would come down. It was getting around 2P. After they were out of my sight for the time for me to get another layer on, I headed back down skinning. I didn't see anyone skiing or riding. I tried to put myself in their boots wondering what they knew about the snow that I didn't. I was happy to get the work in. Coming back near Alta Vista I saw a group of two mired in muck up high on the west side of Alta Vista. I scooted along quickly until past Alta Vista. The snow was light, but not Continental light. For some of the people that fell over or down in the snow, it was quite the chore. I saw some struggles near Paradise as arms and hands had no purchase on the snow at all.

Be very wary of pan point in a east wind. In fact its a no go for me. Always check the telemetry which also gives latest wind direction and speed. And actual field conditions reported above by 0321 along alta vista west facing confirmed the Avy Forcast posted here by Lowell. Digging a pit might have kept you warm but your eyes should have seen enough by then.
We were in Silver basin Crystal mountain where there had been little wind lower in the basin I was seeing no wind effects on the snow . Up near the ridge it was quite a different story.too bad there is'nt enough depth in the trees anywhere yet. On the return to Crystal via the quicksillver run I ski cut a steep nw facing roll just down from the chair offload. I cracked a 8" soft slab that wiped the whole thing. short runout I figured it was side loaded. It had not been skied this year.

I just got back from my AIARE Level I at Mt Baker, so I feel like I ought to chime in with my observations.

I was in that same course so I'll chip in with a bit of info. Our group did a Rutschblock test at around 4400'. It was on a 35 degree slope on an ESE aspect with moderate windloading. It scored RB4. The crack appeared 18" deep. I was pretty suprised with that result and questioned wether or not I would ski on a similar aspect. I'm glad to have taken that course and would recommend it to anyone. I have a whole new respect for this topic.

Merk's RB4 above failed about 4" above the crust on grapple that fell Friday morning and also was about 90-95% a complete block at Q2-Q3.  We had easy shovel shears that identified some facets at the crust and throughout the Snowpack. 

Friday afternoon the temp gradients looked good but as the weekend progressed strong gradients had been identified at the crust.  Watch for faceting near the crust especially in locations that may have received less accumulation.   

I would also watch for near surface facets and possibly surface hoar to develop as a new layer that will be buried by the new snow predicted for tonight and tomorrow.  This could create a touchy scenario with significant step down potential for potentially large slabs.  Particularly in areas that do not receive the number of triggers (skiers), like the North side of Table Mtn.

I took a quick solo trip to Source Lake yesterday. Took the regular trail in, and tested the snow at the rockslides with my ski pole. All consistant powder down to the rocks. Took the Source Lake split and tested the snow at the first open slide area; with my ski pole I was able to easily pull off top 6" of wind crust. Dug a couple of quick pits and found 6" wind crust failed with 7 - 9 finger taps (Q1.5). Being solo I turned back. Not a lot of danger but I didn't want to take even a short ride over rocks with only 2 feet of cover. Previous parties snowshoe tracks stopped there also, but a posthole trail continued on. I also saw hoar frost developing in the lee of rocks; and saw minor stress cracks in the wind crust. With calm conditions I sure there was hoar frost development last night, which could get buried by today's snow. If we get a big dump under warming temps, we could have a deep persistant weak layer for some time.

I did the trip on snowshoes, not really skiable yet. That's my two cents.

This may have been posted already, but there is an info exchange page on the FOAC website. It has recent snow profiles from various areas.

Here is the link.

www.avalanchenw.org/cgi-bin/search_reports.php

Just to throw this into the mix-

I was in Half Price Books in Everett recently and they had 4 or 5 copies of Powderguide: Managing Avalanche Risk for $6 or $7. It's written by 2 europeans and so far I'm enjoying it. Full color with lots of photos and illustrations of concepts (think USA Today). It also has the first english translation of Werner Munter's 3x3 method of avalanche risk reduction (haven't gotten that far yet). The only knock I have on it is the layout of the book; it's kind of chaotic with colors on colors which distract a bit.

Anyways, you can never have too many books in the library!

www.turns-all-year.com/skiing_snowboardi...ex.php?topic=11576.0

With links to this presentation by NWS:

www.wrh.noaa.gov/sew/Dec20-21WinterStorm/player.html

Good info on avy danger, especially toward the last few slides (no pun intended)...

It's amazing how insightful it can be to walk around in the evolving event that shapes the forecast. We had the "opportunity" to walk around in the bitter cold of the northeast winds of Monday around Table Mtn., both north and south, and found that on eveything from northeast around east to southwest, walking near ridgetops under a little prominence that had a 30+ degree slope on it caused the newly slabbed fresh snow from Saturday (which on Sunday had been non-coalescent but now was wind-stiffened into a slab) to break above the skier and run on the ice crust. Once one entered below ridge levels, however, the north aspects were noncoalescent powder and stayed that way all week, with obvious slow bonding to the crust as the week went on. It will be interesting to see if this layer can still react that far down after the new cycle, though I expect probably it will be very unlikely. Just reinforces for me how awesome reports like the Rogers Pass report, from folks walking around in it and testing it every day, are.

NWAC:

If this were not enough for future concern, reports
Crystal Mountain from early Tuesday morning indicated
widespread surface hoar had formed overnight. If the
surface hoar gets buried by expected low wind snowfall
Tuesday night it may be a recipe for dangerous conditions
to develop once loaded by heavier denser wind deposited
snow expected in the near future!

Be careful, after this next storm, in the Crystal BC - dig your pits boys and girls

cd

I know everyone reads these without me reposting here, but the emphasis is mine:

Recent moderate snowfall has been received in most areas during the past few days. For the most part this recent snow is quite light and fluffy, and intermittent moderate winds have generally transported this onto lee slopes where mostly 6-18 inch soft slabs and considerable avalanche danger exist. These lee slopes are predominantly northeast to southeast exposures near higher ridges and west facing slopes near the passes. Weak layers within our still relatively shallow snowpack are many and very significant, ranging from buried surface hoar layers to intermediate or advanced facets to just really weak low density snow layers. This is perhaps the weakest snowpack structure that I have observed in late December for over 20 years, and many field reports of wading or wallowing in the snow at or near the ground when one steps off the packed trail seem to corroborate this assessment. The only positive aspects of the current snowpack in terms of BC avalanche danger is the relatively lack of cohesion in the near surface snow and the still relatively shallow depth that is allowing for some vegetation and terrain anchoring of this fragile snowpack below about 4 to 5000 feet.

Overall, our delicate snowpack is primed for a rapid and dramatic increase in the danger when loaded by heavier and more normal Cascade snowfalls. Unfortunately, in order to start putting the daily impact of these persistent weak layers of facets and surface hoar behind us, we need substantial loading by heavy dense snow, high winds and/or rain. Although this kind of weather is expected to arrive beginning later Friday and continue for much of Saturday, the current magnitude of frailty that our snowpack embodies may take many such storms to build a strengthening bridge over these buried weaknesses...and even then these flimsy layers may re-emerge as problems next spring. In short, this weekend and especially Saturday may be an excellent time to risk your health away from the mountains by shoveling your walk, exchanging your gifts at the mall, or trying out some new high-tech lowland gear.

Good point lordhedgie, I just read the forecast today and was going to add the same thing to this discussion - be careful out there! I'll likely hit the resort this weekend, and will probably carry my avy gear.

I dug a quick pit on Hyak around 7:30 this morning. I'm not very scientific but a littler under two feet of loose snow on top of packed snow is what I saw. It didn't take much to get all of the loose snow to slide in the pit, basically just sliding the shovel behind the block and it went. I had a fun low angle run and didn't oberve anything sliding as I skied out. The highway thermometer was at 29 F when I left. Hyak is groomed to the top which made access a breeze. I did snag the top of a lil christmas tree which sent me into a beauty of a face plant.

my report from Dec 15th

www.turns-all-year.com/skiing_snowboardi...ex.php?topic=11524.0

Stevens has gotten 2-4 feet of light and dry since then, it has been cold since then, and now it's warming and dumping. I encountered at least three very week layers even then in what amounted to an overall dry snowpack except for the above freezing slush at the bottom. NOAA commentary is saying that this is the weakest (in general) snowpack in two decades. So these coming storms warrent a huge amount of caution and attention. From all the forecasts I've read it's a set up worse than last year.

-j

Anyone have more info on the slides on Friday at Hurricane Ridge that were mentioned on the NWAC report?

<snip>
Field reports received late Friday from the Hurricane Ridge area in the Olympics indicate that several skier triggered soft slabs were released, some running an estimated 800 vertical.
<snip>

IMO the Cascade snowpack is developing in a eerily similar manner to that which occured in the Kooteney/Revelstoke area in 2002/2003 (in which 19 people were killed in avalanches). During that season Canadian avi bulletins continued to warn of very deeply buried persistant weak layers, from late November. Keep a close watch on nwac's advisories and snowpack analysis; as digging pits to near ground level is above all else, impractical.

Just a few additions to BirdDog's post and a few other posts here. In 2003 the problem was layers that *weren't* deeply buried. ( BirdDog, maybe you meant "very deeply buried" relative to the total height of snow? ) The snowpack was much thinner than usual in 2003. As most people here know, the large fatality count in 2003 ( in BC ) resulted from two incidents in which a large number of people were simultaneously placed in harm's way. Either of these events could have happened in any year ( with any snowpack ) as recent events have shown.

It doesn't really matter if this year's snowpack is set up worse than last year's snowpack because no one here, myself included, is going to stop skiing. Therefore, the first line of defense is guarding against perceptual errors because such errors are always more dangerous than the state of the snowpack. Sorry to get metaphysical but the snowpack just "is". I mention this because there have been some pretty insane posts in the Trip Reports with respect to perception of instability ( along with some interesting errors and misconceptions being passed around in this thread. ) Perception of instability has not been mentioned once in this discussion so far. NWAC produces incredible forecasts but those forecasts are simply not applicable at the slope scale.

It doesn't really matter if this year's snowpack is set up worse than last year's snowpack because no one here, myself included, is going to stop skiing. ....

... NWAC produces incredible forecasts but those forecasts are simply not applicable at the slope scale.

What? They absolutely are. That's the idea!

I've got the next five days off to ski with a friend. We'll certainly be skiing, but we may not get onto the steeps at all...

The NWAC forecasts are not applicable at the slope scale. These products are applicable at the synoptic scale and sometimes at the meso scale, i.e. "in the general case" but not "in the specific case". NWAC forecasts are great but their bulletins do not include information about specific slopes. It is dangerous to rely solely on a synoptic scale or meso scale forecast when making decisions about a specific slope. ( That's why most people read the bulletin and integrate information about current conditions during their outings. ) Doesn't seem like many people on TAY make go/no decisions based solely on the bulletin because the trip reports show that lots of snowpack evaluation takes place during outings. Anyway, my point was that the actual state of the snowpack is much less important than making sure that perception of instability and reality of instability are aligned prior to decision-making.