| Throughout this snow/avalanche website, we issue a warning to: "Remember that pockets of instability rated one level higher hazard than the forecast for the day will likely be found in parts of the area". The picture below is of the Scotch Bonnett incident near Cooke City, MT on 12/16/06. This incident, which resulted in the burial and death of a snowmachine rider from North Dakota is a graphic example of what we mean. The hazard forecast for that day was HIGH, which alone, should have been reason enough to cause any rider to avoid such extremely steep terrain. What those high-marking the slope didn't recognize was that there were "pockets" of EXTREME hazard held up by the rocky crags--and supported by the lower slopes. The first few high-marks in the left side of the bowl didn't result in a slide. However, when the two riders ran further up under the rocky crags, they finally hit a "pocket" of extremely unstable snow. As a result, the lower slope failed, and all of the upper slope also failed (since it was no longer supported)--thus pulling out the entire bowl. This same type of situation often occurs when the general avalanche hazard for such an area is rated as CONSIDERABLE, or even MODERATE. Survivability of this type of avalanche is almost impossible. Click to enlarge this thumbnail....... |
For further understanding of the "pockets of instability" and
"plus-one hazard rating" concepts we refer to in this web site
related to hazard forecasts it is suggested you study the
following article:
The Avalanche Review, VOL. 6, NO. 4, MARCH 15, 1988
Copyright © All Rights Reserved; AAA
Hazard Ratings May be Hazardous
by Jill Fredston
The interaction of three main variables; the snowpack, weather, and terrain determine whether an
avalanche hazard exists, a fourth, human, variable must be added. Without people or property, there
is no hazard.
As leader of the now defunct Alaska Avalanche Forecast Center, I was frustrated by the four basic
avalanche hazard definitions used by the majority of the U.S. forecast centers in public backcountry
forecasts. I felt strongly that we could produce accurate snow stability forecasts but could not predict
what level of hazard backcountry travelers would create for themselves. We all know that it is very
possible to go out during a period of low instability and create a high hazard for ourselves through
poor route-finding. Similarly, it is possible to travel safely during periods of high instability by careful
choice of slope angles and routes.
The basic rationale for the use of hazard categories in backountry forecast is that they allow users
with diverse avalanche experience to readily perceive the level of danger, identify trends (i.e.
whether the hazard is expected to stay the same, increase, or decrease), and compare conditions
over time and between areas. Also, they help to standardize the formats of the various forecast
center products and thus are felt to minimize the public's confusion. Generally, the public forecasts
state the overall hazard category for each forecast area and then are backed up by site specific
information.
Over a period of several years, I became convinced that the hazard levels were potentially hazardous
in themselves. First, interviews revealed that users tended to focus on the stated hazard levels and
ignore or filter the rest of the message. Secondly, the use of hazard levels seems to inadvertently
encourage people to accept the forecast as an end product--an assumption that has repeatedly
gotten victims into trouble is: "the recording said the hazard was low-moderate, so we didn't expect
to get caught".
Ideally, users should be encouraged to use the forecast as one of many critical pieces of information
in THEIR OWN ongoing decision-making process and the forecast should provide the basic
wherewithal so that even a user with limited avalanche awareness can do this. The importance of this
is underscored by the fact that backcountry avalanche forecasts are regional in nature but the
snowpack is highly variable. It is even further underscored by the fact that of the various activity
groups, backountry recreationalists lead the nation in avalanche fatalities and the majority of
avalanche accidents are human-triggered. In Alaska, over 95 percent of the avalanche victims in the
last decade triggered the slides that caught them.
I began to experiment. I moved the statement of hazard levels from the beginning of the message to
the end in an attempt to focus the listener's attention on the content of the message. That seemed to
help except during those uncomfortable periods when the snowpack was mostly stable but had a few
nasty, isolated areas just waiting for human triggers. When the hazard was "moderate" or as some
would gave it, "low-moderate", users often perceived any description of hazard as an attempt by the
forecast center to, in the words of a user, "cover its tail".
My next step was to eliminate the use of hazard levels altogether and just produce a detailed snow
stability assessment/forecast. This worked well for users with some avalanche knowledge but was
more difficult, at least initially, for the inexperienced because they had no ready measure by which to
compare conditions yesterday with those of today--or the snowpack in one location with that in
another. I then knew that I had to use some kind of rating system.
So I switched from avalanche hazard ratings to snow instability ratings. These ratings were an
obvious take-off on the accepted hazard terminology. The definitions are as follows:
LOW INSTABILITY: Mostly stable snow. Natural and human-triggered avalanches are unlikely except in
isolated locations on steep, snow-covered slopes and gullies.
MODERATE INSTABILITY: Areas of unstable snow. Natural and human-triggered avalanches are
possible on steep snow-covered slopes and gullies.
HIGH INSTABILITY: Mostly unstable snow. Natural and human-triggered avalanches are likely on steep
snow-covered slopes and gullies.
EXTREME INSTABILITY: Widespread unstable snow. Avalanches are certain on some steep,
snowcovered slopes and gullies. Large destructive slides are possible.
These ratings worked well! Users of all experience levels seemed to be hanging up the phone with a
clear understanding of the dominant factors influencing snow instability in each forecast area and
were alert to clues indicating such instability. They had a good feel for the likelihood of natural or
human-triggered releases during the forecast period. They were also aware of expected trends in
snow instability and the reasons for these changes.
We as forecasters were no longer putting a misleading label on the product we could offer. Avalanche
hazard is relative to where the traveler is standing and under what conditions. Snow instability is
relative to the strength of the snow and the forces applied to it. We were forecasting snow instability
based on available snowpack, weather, and terrain data but were no longer presuming to forecast the
highly unpredictable variable of human decisionmaking.
You may argue that all this is a question of semantics. Certainly, the most important part of any
forecast is the content. a forecast must be as specific as possible, accurate, and concise yet
educational. Semantics ARE important though-the misleading hazard language equates to false
advertising and thus inadvertently undermines the credibility of a forecast.
Hazard ratings may work for roads, railroads, and ski areas where public access can be regulated and
avalanche control is an option. In the backcountry, however, the decision-making so critical to a good
hazard evaluation is ultimately the responsibility of the traveler. Whether or not an avalanche
accident occurs depends, to a large extent, on whether the backcountry traveler allows it to happen.
In the backcountry avalanche forecasts, the variable being forecasted is snow instability and
therefore the terminology used should reflect this. The use of snow instability ratings rather than
hazard levels encourages listeners to use the forecast in the way in which it is intended--as a tool.
While in the backcountry, travelers must then continually seek clues and key information so that they
can evaluate the hazard, weigh their options, and choose the safest alternative.
The Avalanche Review, VOL. 6, NO. 4, MARCH 15, 1988
Copyright © All Rights Reserved; AAA
"plus-one hazard rating" concepts we refer to in this web site
related to hazard forecasts it is suggested you study the
following article:
The Avalanche Review, VOL. 6, NO. 4, MARCH 15, 1988
Copyright © All Rights Reserved; AAA
Hazard Ratings May be Hazardous
by Jill Fredston
The interaction of three main variables; the snowpack, weather, and terrain determine whether an
avalanche hazard exists, a fourth, human, variable must be added. Without people or property, there
is no hazard.
As leader of the now defunct Alaska Avalanche Forecast Center, I was frustrated by the four basic
avalanche hazard definitions used by the majority of the U.S. forecast centers in public backcountry
forecasts. I felt strongly that we could produce accurate snow stability forecasts but could not predict
what level of hazard backcountry travelers would create for themselves. We all know that it is very
possible to go out during a period of low instability and create a high hazard for ourselves through
poor route-finding. Similarly, it is possible to travel safely during periods of high instability by careful
choice of slope angles and routes.
The basic rationale for the use of hazard categories in backountry forecast is that they allow users
with diverse avalanche experience to readily perceive the level of danger, identify trends (i.e.
whether the hazard is expected to stay the same, increase, or decrease), and compare conditions
over time and between areas. Also, they help to standardize the formats of the various forecast
center products and thus are felt to minimize the public's confusion. Generally, the public forecasts
state the overall hazard category for each forecast area and then are backed up by site specific
information.
Over a period of several years, I became convinced that the hazard levels were potentially hazardous
in themselves. First, interviews revealed that users tended to focus on the stated hazard levels and
ignore or filter the rest of the message. Secondly, the use of hazard levels seems to inadvertently
encourage people to accept the forecast as an end product--an assumption that has repeatedly
gotten victims into trouble is: "the recording said the hazard was low-moderate, so we didn't expect
to get caught".
Ideally, users should be encouraged to use the forecast as one of many critical pieces of information
in THEIR OWN ongoing decision-making process and the forecast should provide the basic
wherewithal so that even a user with limited avalanche awareness can do this. The importance of this
is underscored by the fact that backcountry avalanche forecasts are regional in nature but the
snowpack is highly variable. It is even further underscored by the fact that of the various activity
groups, backountry recreationalists lead the nation in avalanche fatalities and the majority of
avalanche accidents are human-triggered. In Alaska, over 95 percent of the avalanche victims in the
last decade triggered the slides that caught them.
I began to experiment. I moved the statement of hazard levels from the beginning of the message to
the end in an attempt to focus the listener's attention on the content of the message. That seemed to
help except during those uncomfortable periods when the snowpack was mostly stable but had a few
nasty, isolated areas just waiting for human triggers. When the hazard was "moderate" or as some
would gave it, "low-moderate", users often perceived any description of hazard as an attempt by the
forecast center to, in the words of a user, "cover its tail".
My next step was to eliminate the use of hazard levels altogether and just produce a detailed snow
stability assessment/forecast. This worked well for users with some avalanche knowledge but was
more difficult, at least initially, for the inexperienced because they had no ready measure by which to
compare conditions yesterday with those of today--or the snowpack in one location with that in
another. I then knew that I had to use some kind of rating system.
So I switched from avalanche hazard ratings to snow instability ratings. These ratings were an
obvious take-off on the accepted hazard terminology. The definitions are as follows:
LOW INSTABILITY: Mostly stable snow. Natural and human-triggered avalanches are unlikely except in
isolated locations on steep, snow-covered slopes and gullies.
MODERATE INSTABILITY: Areas of unstable snow. Natural and human-triggered avalanches are
possible on steep snow-covered slopes and gullies.
HIGH INSTABILITY: Mostly unstable snow. Natural and human-triggered avalanches are likely on steep
snow-covered slopes and gullies.
EXTREME INSTABILITY: Widespread unstable snow. Avalanches are certain on some steep,
snowcovered slopes and gullies. Large destructive slides are possible.
These ratings worked well! Users of all experience levels seemed to be hanging up the phone with a
clear understanding of the dominant factors influencing snow instability in each forecast area and
were alert to clues indicating such instability. They had a good feel for the likelihood of natural or
human-triggered releases during the forecast period. They were also aware of expected trends in
snow instability and the reasons for these changes.
We as forecasters were no longer putting a misleading label on the product we could offer. Avalanche
hazard is relative to where the traveler is standing and under what conditions. Snow instability is
relative to the strength of the snow and the forces applied to it. We were forecasting snow instability
based on available snowpack, weather, and terrain data but were no longer presuming to forecast the
highly unpredictable variable of human decisionmaking.
You may argue that all this is a question of semantics. Certainly, the most important part of any
forecast is the content. a forecast must be as specific as possible, accurate, and concise yet
educational. Semantics ARE important though-the misleading hazard language equates to false
advertising and thus inadvertently undermines the credibility of a forecast.
Hazard ratings may work for roads, railroads, and ski areas where public access can be regulated and
avalanche control is an option. In the backcountry, however, the decision-making so critical to a good
hazard evaluation is ultimately the responsibility of the traveler. Whether or not an avalanche
accident occurs depends, to a large extent, on whether the backcountry traveler allows it to happen.
In the backcountry avalanche forecasts, the variable being forecasted is snow instability and
therefore the terminology used should reflect this. The use of snow instability ratings rather than
hazard levels encourages listeners to use the forecast in the way in which it is intended--as a tool.
While in the backcountry, travelers must then continually seek clues and key information so that they
can evaluate the hazard, weigh their options, and choose the safest alternative.
The Avalanche Review, VOL. 6, NO. 4, MARCH 15, 1988
Copyright © All Rights Reserved; AAA
