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gb
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PostFri Jan 29, 2021 8:15 am 
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Be sure to read the Avalanche Forecast before going out: https://nwac.us/avalanche-forecast/#/all

For each zone you are interested in, look at the "Full Forecast"

The exposure of the recent raincrust and the gradual accumulation of new snow with breaks between storms have resulted in weak layers overlying the crust. This will not go away in the foreseeable future as snow levels remain low and temperatures cold. It is very difficult to "heal" this type of problem.

Areas having received warm sunshine will have different new and potentially weak layers, depending on the strength of sun crusts.

Going forward, each additional amount of new snow just adds to the potential risks associated with the hazard.
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PostSat Jan 30, 2021 6:35 am 
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This is ramping up this weekend as increasing amounts of snow and rising freezing levels continue this weekend.

When the basal layers are so weak - as reported in many areas - and a hard and icy layer beneath, behavior of slabs is likely to be unpredictable. I'd expect that if there is substantial snow above the crust that even where the new snow doesn't feel slabby, it may still release as a soft slab.
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PostSat Jan 30, 2021 2:30 pm 
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Thanks Gary. This indeed is looking like a kind of unfortunate setup that's been building since the last warm rains. The new snow came in after it was well frozen and it was fairly cold. I have not been checking the forecast details but I would not be surprised if there is also some surface hoar buried down there in sheltered areas given the clear stretches we also have had.
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iRemeberToby
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PostMon Feb 01, 2021 6:13 pm 
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Sadly, we are probably joining the "poor snowpack club" so to speak, as other areas of the country like Colorado and Utah have had notoriously poor, avalanche-prone snowpacks this season. With our maritime climate we are often fortunate enough to avoid the PWL problems that plague those intermountain and continental snowpacks, but our weather lately has been very bad for creating avalanche problems. Sadly, a person died in an avalanche in the backcountry in Park City, Utah recently, the second avalanche death in that zone this season.

So far, NWAC does not have any accidents or fatalities listed on their observations page. That's great news. Fingers crossed it stays that way.

Stay safe out there.
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PostMon Feb 01, 2021 9:55 pm 
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iRemeberToby wrote:
Sadly, we are probably joining the "poor snowpack club" so to speak, as other areas of the country like Colorado and Utah have had notoriously poor, avalanche-prone snowpacks this season. With our maritime climate we are often fortunate enough to avoid the PWL problems that plague those intermountain and continental snowpacks, but our weather lately has been very bad for creating avalanche problems. Sadly, a person died in an avalanche in the backcountry in Park City, Utah recently, the second avalanche death in that zone this season.

So far, NWAC does not have any accidents or fatalities listed on their observations page. That's great news. Fingers crossed it stays that way.

Stay safe out there.

A very close call the other day: https://nwac.us/public-obs/20210130_bagley-basin-below-herman-saddle/
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gb
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PostTue Feb 02, 2021 7:24 am 
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I think to a degree, the more experience one has in a maritime snowpack, the greater the risk that you will not fully comprehend snowpacks especially in the Rockies because it is hard to change behaviors one evolves skiing a different type of snowpack. Snowpacks develop notorious weaknesses when exposed to prolonged periods of dry weather prior to snowfall resuming, as invariably weak layers form during these, usually at least somewhat, cool to cold periods. Those layers can be surface hoar, shallow faceted layers of new snow, facets that form right above or just below a crust (the crust was 32 when it formed), or in the case of shallow snowpacks, the entire snowpack can turn to facets and depth hoar. Think of a sandwich. Obviously, the latter is something we are less familiar with in a Maritime Snowpack; but it is very common in the Rockies and nearer them. For instance, the Purcells near Golden BC on the west side of the Rocky Mountain trench south of Golden, BC often develop snowpacks very similar to that of the Rockies to the east. A friend who for a period managed a helicopter operation near Radium at Panorama once described to me that he considered the base of that snowpack as "a house of cards". He had previously managed the CMH Monashee operation, which is most winters much like a Pacific Northwest snowpack in a better, cooler winter. The Monashees have few extended dry periods.

My experience with potentially weak snowpacks was a winter at Sun Valley, where in backcountry skiing and studying the snowpack periodically, I learned that in areas of shallow snowpack - 3-3-1/2' - the entire snowpack is junk crystals of depth hoar and facets; in areas of snowpack 4-5', there was still considerable weakness; but with a snowpack depth of 6-7', the snowpack was quite strong.

For many years I dug many, many snow profiles at Blewett Pass. In that climate on a typical year, a snowpack shallower than about waist deep @ 37", tended to be weak and could lose 50% of it's strength in a week of clear weather; but when the snowpack was 4 or more feet deep, weak layers could develop near the surface, but the entire snowpack would not turn to rot. But that was with likely an average temperature near 28F at 4000'. With colder temperatures, the critical depth for the formation of depth hoar grains would, of course, be less - as, say, in Sun Valley.

Since I have an Ikon pass, I sometimes look at ski areas throughout the west. Most areas until just recently had shallow base totals (Alta 41"). Mammoth, in California, had a 20-30" snowpack and had received less snowfall all winter than Seattle had in 1968. Then, in the past week, it received at least twice as much snowfall as it had the rest of the winter.
Central Sierra Avalanche Forecast Center

The dangerous snowpacks in, say, Park City, Utah are understandable, but that does not make them predictable in behavior. When the snowpacks have these "Persistent weak layers" the smart money is just to not go there. I would not have backcountry skied this week except in very shallow angled terrain.

About snowpack temperature gradients and faceted snow

Surface hoar formation and problems

Perhaps things could get better from bridging and snowpack consolidation (and new crusts) this week; but at higher elevations, the poor bond at the January 13th crust (heavy rain and strong winds) will still be there. That will likely show up in large spring wet slabs during very warm spring weather (often about the second week of May).
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PostTue Feb 02, 2021 5:33 pm 
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gb wrote:
I think to a degree, the more experience one has in a maritime snowpack, the greater the risk that you will not fully comprehend snowpacks especially in the Rockies because it is hard to change behaviors one evolves skiing a different type of snowpack.

I agree completely. It is not that different than dealing with "a different kind of cold". Years ago, when my wife came out here from Chicago, her dad gave her a big down jacket. He could read a map, and Seattle is farther north than Chicago! Of course it was pretty much useless for a day around town. Either it was way too warm, or saturated.

The opposite is true as well. Head to North Dakota in the winter with a fleece jacket and Gore-Tex and you are freezing. You can't handle the subzero temperatures.

With avalanches, it is a mix here (as is everything in the Cascades). But generally speaking, we can usually spot the really bad days. One factor that is often ignored is that most deaths around here are caused not by a complete burial, but by being pushed over a cliff. We have a lot of cliffs, and it doesn't take much snow to get pushed over one.

In contrast, the Rockies have avalanches on beautiful days, in relatively mellow terrain (no cliffs around). The idea that you would get buried in nice, light, dry snow is really a hard thing to wrap the mind around, but fast moving snow melts, and well, there you are.

Of course as I wrote, we have a mix here. In the lowlands, you aren't likely to get buried in snow on a nice day. But up high we can resemble the Rockies. Just as you want a down jacket in the winter above 6,000 feet, you have to be careful about similar avalanches after several high elevation powder days. And of course, you might be standing at 3,000 feet, but that mountainside goes up to 7,000.
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PostWed Feb 03, 2021 7:42 am 
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Check out the amazing video from Mt. Baker. The avalanche not only went across the flats beneath Mt. Hermann but made an effort to climb the terrain on the opposite side where the people are. https://nwac.us/avalanche-forecast/#/west-slopes-north
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PostWed Feb 03, 2021 11:07 am 
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Field report from the Blewett Pass area -- looks very touchy.

https://www.instagram.com/p/CK0KQO0HyQX/?fbclid=IwAR1pmZRIQM2NJ1l-9P9I0Oe9DeD5JjE0niqi672Yg_CzugJb6oc63mWevFM
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PostFri Feb 05, 2021 5:54 am 
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The images of avalanche activity are super impressive especially in the North Cascades, both east and west. This continues with more snow today and again on Saturday.
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PostSat Feb 06, 2021 6:30 am 
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This continues and is very dangerous. Many reports of new slabs as wide as 1000'. Strong winds and significant new snow today just add to the issue. You can trigger an avalanche from a long ways away. Where it has already slid, a new slab potentially on the crust again develops.

Read the avalanche forecast. www.nwac.us

Personal experience showed me many years ago in a safe area that energy in a similar snowpack can propagate at least 400 yards. I could see that following a powerful collapse (3/4" drop and sideways displacement) by trees shaking at that 400 yard distance. On another trip near Mt. Baker, I saw an 18" crown that went about 600-700 yards wide.

In Canada, in really bad snowpacks - like 2003 - extreme examples were observed to have released about 3 miles wide. A friend of mine in the Rockies told me that skiing in the valley bottom of Mosquito Creek that he released an avalanche three thousand feet above him that ran to the valley floor some distance from him.
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PostSat Feb 06, 2021 6:58 am 
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Scary! Good thing they where in a somewhat safe spot. Looks like one of them was struggling to move.

Looks like I picked a good weekend to rearrange the garage.
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RumiDude
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PostSat Feb 06, 2021 10:49 pm 
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Near Salt Lake City four skiers were killed in an avalanche.

From the article: "Fifteen people have died in avalanches during the last week in the United States, the most in a seven-day period since 1910, according to Karl Birkeland, the director of the National Avalanche Center, which is part of the U.S. Forest Service."

Be careful out there!

Rumi

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"This is my Indian summer ... I'm far more dangerous now, because I don't care at all."
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PostTue Feb 09, 2021 11:36 am 
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East Slopes Central current 2/9 Avalanche Forecast:

https://nwac.us/avalanche-forecast/#/east-slopes-central

With image of fatal avalanche scene.
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PostMon Feb 15, 2021 7:29 am 
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Potentially really dangerous today, moreso Tuesday, continuing into Wednesday.

High Hazard www.nwac.us

Recent weaknesses and crusts, low density new snow with strong winds, topped with increasingly dense snow after about noon today, with further warming Tuesday. Think of the new snow as being top-heavy.

A cornice fall or avalanching new snow could release much thicker buried slabs.
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