Wenatchee Mtns avalanching & spatial variability

The point of this: heed the available excellent avalanche hazard information, but evaluate and know what is going on.<br><br>Today (near Blewett) in the Wenatchee Mtns I saw natural avalanching at 5600' elev. with a 10 to 12 inch crown on north facing slopes (cliff bluffs) from 40 to 50 degrees angle. Most were insignificant, however one was sizeable. I was in the area last Saturday and saw the snowboarder-triggered avalanche crown and deposition. Several skiers tracked that slope Saturday. Today I noted that another skier or boarder must have released another small avalanche near the first after I was there. Thirdly, today it appeared that natural snowfall fell on the bed surfaces from the above releases and then released naturally yesterday or the day before. Those releases fell to a flat maybe 150' distance.<br><br>The significant natural release was from another starting zone in another north-facing path to the south of the above mentioned path. The fracture was 10 to 12 inches at the crown, propagated across some rock bluffs that roll up to 40+ degrees angle at 5600' elev. The debris ran several hundred feet down and left a smooth bed surface, and was perhaps 150' wide (estimate). The debris pile would easily bury a car. It did not run the full length of the path. I ski cut the remnants by the crown, then skied fairly good deep snow just outside the bed; it became pretty crusty by 5000' elev.<br><br><br>Great forecast below (large parts deleted):<br><br>BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON <br>CASCADES AND MT HOOD AREA<br>NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON<br>0830 AM PST MON JAN 16 2006<br><br><br> <br>EAST SLOPES WASHINGTON CASCADES-<br>...AVALANCHE WARNING...<br>Moderate avalanche danger below 7000 feet gradually increasing Monday morning and significantly increasing Monday afternoon, becoming high above 4 to 5000 feet and considerable below. Further gradually increasing danger expected Monday night becoming high above 3 to 4000 feet and considerable below. Danger decreasing Tuesday morning becoming considerable above 5 to 6000 feet and moderate below, with a further slow decrease Monday afternoon becoming considerable above 6000 feet and moderate below. Little change in the danger Tuesday night.<br><br><br>MONDAY, MONDAY NIGHT-<br>Light to occasionally moderate snow should increase later Monday morning, with periods of moderate to heavy rain or snow, increasing winds and rising freezing levels expected Monday afternoon and night. This should lead to a substantial increase in the danger as increasingly dense snow or rain are deposited over existing low density surface snow layers over either a crust or heavier denser wind slabs. As a result, generally high avalanche danger and relatively sensitive natural and human triggered slabs should become increasingly likely later Monday afternoon and night, with greatest danger in most areas expected <br>to develop on northwest through northeast exposures near higher ridges. However, near the Cascade passes&#8212;where a cool easterly flow should provide some insulation from the warming aloft&#8212;associated winds should accentuate the danger on west facing slopes with a rapid increase in the danger expected near the passes Monday night. With warming, strong winds and high precipitation rates expected to continue through midnight, very dense wind or wet slabs should develop and slabs of 2 to 3 feet <br>or more are likely, with some isolated larger slabs of 4 to 6 feet or more possibly releasing to the crust formed late last week or to some low density snow layers or buried surface hoar formed last Wednesday. As a result, back country travel in avalanche terrain is not recommended Monday afternoon and night, and any travel should be confined to windward ridges or lower angle slopes well away from avalanche path runouts. (end quote)<br><br><br><br>Saturday, after skiing from 5900' on the above mentioned north slope, we saw pits being dug by the treeline at around 4800' elev., and mentioned that a small avalanche had been set off up above. I was somewhat puzzled to see the below information, since the area of the pits did not correlate to the avalanche starting zones in the area: <br><br><br> <br>BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON <br>CASCADES AND MT HOOD AREA<br>NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON<br>900 AM PST SUN JAN 15 2006<br><br><br><br>Near Blewett Pass about 30 cm of fist to 4 finger snow was very well bonded to a strong crust with no shears found and stable conditions about 5000 feet. (end quote)<br><br><br>The area is prone to faceting in open areas and the faceting is especially persistent on north facing relatively wind-protected terrain. Today I easily kicked some 10-12 inch slabs off of a ridge meeting that description.<br><br>It would appear that those weaknesses will persist until another soaking warm cycle or perhaps until bridged by an overlying strong snow structure.

Near Blewett Pass about 30 cm of fist to 4 finger snow was very well bonded to a strong crust with no shears found and stable conditions about 5000 feet. (end quote) <br> <br> <br>The area is prone to faceting in open areas and the faceting is especially persistent on north facing relatively wind-protected terrain. Today I easily kicked some 10-12 inch slabs off of a ridge meeting that description. <br> <br>It would appear that those weaknesses will persist until another soaking warm cycle or perhaps until bridged by an overlying strong snow structure.<br>

<br><br>Of course things have changed a lot since the weekend with about 10" of additional snow in the last storm. In most cases (except above treeline where wind-affected) the depth of the slides you mention (10-12") correlates with the new snow from that storm. The surface prior to this storm varied from rough crusts with facets to well-bonded rough crusts, perhaps even some surface hoar, and near surface facets.<br><br>It would appear to me that near and above treeline on generally north through east aspects there are some very large pillows that are somewhat stabilized. Nonetheless they may still be triggered when not well-supported (convex). Those slabs could be very deep and would release to the crust.

What I was describing can be described as spatial variability in the snowpack. This is an important concept. While a homogenous snowpack existed at 4800' or so elev., the upper slopes directly above @ 5400' elev. had a weak slab with weaknesses at the same time, and those weak layers are persisting this week.<br><br>Directly above the pit study by about 800 vf was active artificial avalanching Saturday (I saw) and probably Sunday (saw evidence of on Wed.), and natural releases of newly fallen snow over the same bed surface that had been previously artificially released in the following days.<br><br>Sunday I saw north facing crowns from slabs that had released from the ridgetop on the SE side of Mission Ridge.Today (Thursday) I ski toured to the NE of Mission Ridge Ski Area above 5300' elev. and saw many crowns from slabs on N to NE facing steep starting zones that have released naturally this past week. There is now some new snow on those bed surfaces again, but the crowns are clearly visible.<br><br>Spatial variability. Has anyone else read about the Swiss Army group whose Rutschblock test on an Alp slope was deemed to indicate relative safety just before the rest of the slope avalanched and caught some of the group? That would be a sort of comical tragedy- an area with a Rutsch block remaining on a slope after the snow to the side of it had avalanched. Such may be possible on the slopes that I discussed, as some aspects seemed to be quite homogenous up high, as well, while others had natural avalanching.<br>

I don't recall the source, but I do recall reading that there tends to be great spatial variability, and that even a few test pits that have been somewhat carefully selected for location can fail to indicate the risk that is right next to the pits. I don't know how well supported this premise is, but it makes gut sense to me, and leads me to typically want to follow Gary's advice (from L1 training years ago) to think not only about probability of sliding, but salso the consequences of being caught in a slide on any given slope (i.e. avoid nasty terrain traps and humongo slopes even when you think it is fairly safe...).<br><br>"To know that you know what you know, and that you don't know what you don't know, that is true knowledge."

I forget where I heard this:<br><br>As overall hazard increases, so does spatial variability.<br><br>Think about that. The higher the overall hazard, the more likely that an observation at one point will NOT be representative of the hazard at another point.<br><br>I think this helps explain why people with avalanche training are just as likely to be caught as people without. With training, we venture farther into the gray zone between clearly safe and clearly dangerous. We ski on Considerable hazard days. But if we forget about things like spatial variability, Ruschblocks, snowpits, and other training can become just an elaborate trap.

Weather data and knowledge of terrain characteristics in regard to avalanching are important. It is impressive that the NWAC forecasters do what they do so well largely from inside their Seattle office, using some field reports and some personal forays into the field. One can estimate quite a bit from weather data, and then test one's hypotheses in the field.<br><br>Safe routes can often be found. I will not ascend in the face of avy hazard unless there is a safe route. I do measure the slope angles and ascertain the aspect by compass. It is my habit to get above the hazard, after evaluating it on the way up, then test it from the top. The point about evaluating the results of an avalanche is a good one- I like to drop from safe terrain to safe terrain or from thick, solid tree island to the next. My personal habit also is ski down from safe area to safe area with one turn left or right out of a potential avalanche. On my regular tour routes ( I have lots of ski days) I like to go back and see that my safe travel routes are confirmed after an active avalanche cycle. It is also instructive to see that a "safe travel route" is but a few feet away from active avalanching. One needs to understand relative hazard conditions- some conditions, usually warm and wet after cold and dry, can exceed one's expectations in that things avalanche where one does not expect.<br><br>The data that indicates a high incidence of "experts" being entrapped refocused my attention (although I usually remain afraid having been caught and carried twice in 26 yrs.- never want to repeat that). Aside from the "expert" thing I feel that it comes back to self discipline/ self denial of sweet pow turns sometimes. Back in the day, avalanche workers that I knew who had thrown bombs in a ski area in the AM and easily got significant avalanching results then went bc skiing in the afternoon after work and became entrained in an avalanche. <br><br>The other big problem is group dynamics. invariably when I am with more than two or three in the party, errors are made, more than one skier is exposed, or the entire group gets in a gaggle beneath hazard while talking and socializing. In regard to groups, I would challenge those traveling on avalanche terrain to behave as if they are alone. Complete burial even with transceiver has a significant incidence of fatality. Judging from the posts here on the topic, and sorry to say this- not intended to offend- many can find a transceiver within only about 15 minutes, so I would not even consider that a viable means of rescue.<br><br>I appreciate the discussion and hope some will be motivated to learn. Part of my motivation is to air concepts and self check my interpretation of the literature and my observations. In the end we are exposing ourselves to the potential of being killed- much like driving a car at 60 MPH. We can choose the manner and habits in regard to driving that car.