Knowing, Part I

I could feel at the time, there was no way of knowing—Roxy Music

From Wikipedia: Holism (from ὂλος holos, a Greek word meaning all, whole, entire, total) is the idea that all the properties of a given system (physical, biological, chemical, social, economic, mental, linguistic, etc.) cannot be determined or explained by its component parts alone. Instead, the system as a whole determines in an important way how the parts behave.

In my last post, I outlined some priorities for learning snow safety. I'd like to provide a few additional simplifications.

• A.) Understand yourself and the people with whom you ski.
• B.) Develop a mental model of the physical processes taking place in the mountains.
• C.) Integrate A and B via correct backcountry avalanche forecasting procedures.

Once you have some basic information, you can start to apply correct backcountry avalanche forecasting procedures to "the avalanche problem", and produce further refinements. You can boil backcountry avalanche forecasting down to its essence in the following manner:

The goal of backcountry avalanche forecasting is to minimise uncertainty about instability by prioritising information acquired through an understanding of the physical processes taking place in the mountain environment while accounting for the possibility of human error.

Of course, all of this is much easier said than done, especially since there are always shortcomings in the data. In terms of cognition, these shortcomings combine with well-known limitations of our psychology and variations in our perception to blunt our awareness and numb us to the effects of uncertainty.

All of which ultimately increase our vulnerability to serious errors. Following correct procedures greatly reduces the chance of error ( and the consequences ).

It's the difference between knowing and not knowing.

2011-2012 Avalanche Season

I guess it's the price of love; I know it's not cheap—U2

Author's Note: Okay, as a "treat", I've written a grand ramble.



Part I. The Dynamic Nature of Backcountry Avalanche Forecasting

Backcountry avalanche forecasting is concerned with minimising uncertainty about snowpack instability at a specific time and place. Recreational backcountry skiers are very good at making observations, but often seem confused about how to prioritise their observations. Here are some rules and regulations:

Datum	Description
Class III	Weather Factors. Mostly numeric data; there is high uncertainty about the relationship between weather data and avalanches. This includes observations such as warming, cooling, wind direction, new snow, and rain. The snow may or may not be unstable.
Class II	Snowpack Factors. Mostly rule-based data; medium uncertainty about the relationship between snowpack data and avalanches. Includes the results of instability tests ( especially shear quality / fracture character ), snow profiles, ski testing. Are there signs of instability? Is skier-triggering possible?
Class I	Instability Factors. Mostly event-based data; low uncertainty about the relationship between instability factors and avalanches. Cracking, whumpfing, avalanches. Skier-triggering is possible. Is there a significant chance of releasing an avalanche of Size 2 or greater?

Weather Examples
If there is heavy accumulation of new snow, with wind, and warming, and whumpfs, then I'm going to be super careful because I know the snowpack is unstable. However, at this point I don't really care about the heavy accumulation, the wind, or the warming. I'm only concerned with the whumpfing, because it is a crystal clear sign of high snowpack instability.

In this example, I've given the most weight to the observation that reveals direct information about instability. It's also worth mentioning that whumpfs can occur with new snow, cold temperatures, and calm conditions. The endless variety of parameters and outcomes is why weather data has an inherently uncertain characteristic.

In the absence of direct signs of instability, I'd give the most weight to whatever observations revealed the most information about instability. In this example, I would assign a higher priority to recent wind/warming than to new snow amounts because wind can turn small accumulations into thick wind slabs and warming can destabilise the existing snowpack. This is one place where a well-rounded understanding of mountain weather, along with the physical properties of snow, makes prioritisation much easier.

Snowpack Examples
In the case of snowpack factors, I would assign higher priority to shear quality / fracture character than to the number of taps in a compression test. Mostly because the number of taps only provides indirect information about instability ( an index of instability if you will ), whereas shear quality/fracture character reveals fairly direct information about instability. I use the extended column test in a similar fashion. It's important to note that research in Canada ( by Cam Campbell et al. ) has found that there is less variability with respect to shear quality than for the number of taps.

The Avalanche Handbook compares improper use of snowpack tests to the lottery and Russian roulette. For this reason, and for other reasons that I won't discuss here, I really don't use snowpack tests or formal profiles all that often because I'm really only looking for a few specific things when I dig:

• What is the layering?
• What are the crystal forms?
• Does hardness increase uniformly with depth?

I perform formal snowpack tests only when I'm curious about the shear quality and fracture character of something specific. Very often, finding a weakness is enough to make me strongly consider alternate plans without the need for actually testing the weakness. I suppose this is my way of saying that I assume it is possible to release avalanches on most weaknesses.

For the record: I'm providing this information here as an example of how I prioritise observations and sort out red flags; this is just my personal style. You probably shouldn't do things this way unless you understand snow metamorphism from cloud-to-ground.

Backcountry Avalanche Forecasting Is Dynamic
Anyway, this leads to the next concept: the dynamic, ongoing nature of backcountry avalanche forecasting is one thing that quite a few recreational backcountry skiers don't understand very well. I have actually witnessed backcountry skiers comparing and contrasting signs of stability with signs of instability. Backcountry avalanche forecasting is framed around instability, and searching for signs of stability ( AKA "searching for supportive evidence" ) amounts to doing it backwards.

And feel free to disregard redundant information: research by Makridakis shows us that while additional information can increase your confidence in a conclusion, the relationship between confidence and accuracy is tenuous. Futhermore, Makridakis found that redundant information can actually decrease the accuracy of predictions. The correct procedure: continually revise your forecast as you integrate new observations. Continually ask yourself, using the data interpretation guidelines above, does the data reveal anything about instability? A single piece of data that reveals information about instability has the power to completely change the forecast from "potential instability" to "high instability". New plans are in order if that's the case.

Regardless of any of my prattling, make conservative decisions when your uncertainty is high for any reason. High uncertainty is a sign that you lack the information required to make sound judgments about risk. And remember, desire and uncertainty are an especially dangerous combination when unmanaged.

The rest of the post contains musings and additional information. There is a lot of opinion, so please take it with a grain of salt.

Part 2. How Do I Learn Snow Safety?
Okay, it's time to get out the salt. Keep the salt out until the very end of this post.

Having resumed posting for the season, people have started asking questions about how to learn snow safety. With good reason, most people will never have the interest in or need to develop a professional level understanding of snow safety, but that doesn't mean they aren't interested in gaining a deeper understanding. Maybe it's because they love powder skiing, ski mountaineering, or powder skiing mountaineering. Maybe it's because they love their friends and family.

I'm not sure how to answer this question because I learned snow safety through a blend of frozen fingers, the terror of bad decisions, and lots of studying. If I had to do it all over again, I'd set the following goal: develop a reasonably detailed mental model of the physical processes taking place in the mountain environment. Here are the main study areas:

Learn About	Description
Yourself	Invaluable since we create the hazard. Incredibly difficult. Easily #1. ParksCanada has maps of popular backcountry skiing locations and one of maps actually asks the user "what brings you here today?". In a similar vein, Martin Volken gave a talk at the 2008 Northwest Snow & Avalanche Summit. His presentation asked "why are we going to the mountains?" It was a wonderful talk.
Snow Metamorphism	From cloud to ground. Utterly invaluable. Better learned while in the kitchen with a hot coffee and toast than from inside the belly of the white whale. ( Free study material. )
Mountain Weather	Mountain weather. Invaluable. It's probably easier to learn in the safety of your living room. However, you can also learn a lot about mountain weather by standing on a ridge top while 130 km/h wind sucks the air from your lungs and resurfaces the skin on your face. Yes, afterwards you'll look younger on the outside, but you'll feel older on the inside! ( Free study material. )
Avalanche Forecasting	Avalanche forecasting from Chapter 6 of The Avalanche Handbook. The material is simply amazing and it will help you tie your knowledge together brilliantly. You know what, I'll be honest, it's a tough chapter but it's not certainly not even in the same realm as algebra. It's also not as tough as thinking about how your boyfriend of 15 years will react if someone tells him that you've been killed by an avalanche. ( More free study material. )

My bottom line advice: start out with an AIARE Level 1 class if you're in the US. Check with the CAA if you're in Canada.

Learning About Yourself
This is important on any number of levels, especially if you'd like to get married and stay married. It's also important because learning about yourself teaches you so many things. As with everyone who is approaching 40 as quickly as I am, my personal journey could fill a book or two. Actually, the mistakes alone could fill a book. ( Or maybe two books. But definitely not a library. At least I hope not. )

In all seriousness, I have had my share of moments, including days spent gliding through snow that was hovering right at the razor's edge of serious instability. Gain enough experience and you'll learn what snow feels like when it wants to move. Learn enough about yourself and, unlike me, you'll probably be smart enough to avoid that situation in the first place.

Bottom line: Backcountry avalanche forecasting is much easier when you stop eating idiot sandwiches ( and I ought to know! ). Give introspection and inner peace a chance.

Learning About Snow Metamorphism
I sometimes hear people talk with disdain about the subject of snow metamorphism, especially during conversations about avalanche education. What is snow metamorphism anyway? Well, I have a fairly inclusive definition of snow metamorphism. To me, snow metamorphism starts during crystal formation in the clouds and it ends when the last of the snow melts in the summer. But at any rate, it seems to me that a great many people confuse snow profiles and snowpack tests with snow metamorphism when they're not even remotely the same thing. Snow metamorphism describes how the snowpack forms and understanding the physical properties of snow, including its behaviour from cloud-to-ground, is incredibly useful.

If you don't understand snow metamorphism, then the vague results often associated with snowpack tests aren't very useful. Of course, if you don't understand snow metamorphism, you won't understand why snowpack test results are often vague any more than you'll understand why snow metamorphism is so important in the first place. People who understand snow metamorphism from cloud-to-ground rarely base go/no go decisions on a snow profile. Why is that? It's because they understand the inter-connections between terrain, snowpack, and weather.

Is it important to observe crystals as they fall from the sky? Yes, it certainly can be very important, especially if crystal size increases markedly during a day of powder skiing. This is a sign that a warmer temperature regime is passing over the mountains, and warmer air carries more water vapour. If the day started out cool, an increase in crystal size can indicate the potential for upside down snow. What about poking around in the snow and observing crystal forms? Yes, also important. After all, the snowpack is a living, breathing beast that you must understand if you want to play in the mountains during winter.

Bottom line: Learn about the life cycle of snow.

Learning About Mountain Weather
It's complicated, right? That's putting it lightly indeed. Mountain weather teaches you a lot about snow safety because the unreal complexity of mountain weather—especially the chaotic interaction of weather and terrain—is incredibly humbling. Once you understand the complexity of mountain weather, it's much easier to understand why the snowpack is so complicated. Once you understand the adiabatic lapse rate... well... actually cold air advection is more interesting, but at any rate.

Once you accept the complexity of the interaction between terrain and weather, and its effects on the snowpack, you'll know—I mean you'll really know deep down inside—that it's utterly and stupidly pointless to try and outsmart the snowpack. You'll be forever done with all that pseudo-scientific speculation that always happens during water breaks because you'll understand what you can't know and why you can't know it. Spatial variability won't be a puzzle; it'll simply be what is.

With enough knowledge about, and experience with, mountain weather, it is possible to discern patterns of instability and gain valuable insights about where you shouldn't travel. But here's the thing: having enough knowledge and experience about mountain weather will almost certainly convince you that discretion is the better part of valour.

Bottom line: Mountain weather will amaze and humble you. Learn mountain weather basics for free. Or learn about avalanche weather for free.

Learning About Backcountry Avalanche Forecasting
It's funny how often I answer the same questions. I've even written posts on this blog to answer the same question after it was posed to me by three different people. Last season I received about 100 questions, and most of them were related to backcountry avalanche forecasting. Occasionally the question will involve a dispute between two parties who couldn't agree whether or not they made the right choice for a go/no go decision. Myself, I like to stay out of disputes, so I always decline to answer those questions.

I'm not really sure about the level of knowledge or experience of the people who ask questions, but it is always very clear to me that these nice folks don't have a very good understanding of how backcountry avalanche forecasting works. The questions invariably boil down to the following: I have these observations; what should I do in  this situation? As I said above, most recreational backcountry skiers are very skilled at making observations, but far less skilled at prioritising. Prioritising observations is exactly how one minimises uncertainty about instability, and therefore it is at the very heart of backcountry avalanche forecasting.

If you read this blog with any regularity, you are probably well-aware of my near fanatical devotion to The Avalanche Handbook. However, in this case I'm going to make a rare criticism. The chapter on backcountry avalanche forecasting ( called "The ABCs of Backcountry Avalanche Forecasting ) is a confusing mix of weird rules, strange procedures, and useful facts. I didn't really learn anything that I didn't already know, and while I think you should still read the chapter, I've probably read it a dozen times, and it's never made much sense to me. ( I could be stupid! )

Luckily, chapter 6, ( called "The Elements of Applied Avalanche Forecasting" ) is quite brilliant. The authors are quite careful to note that the chapter outlines a theoretical framework for avalanche forecasting, but whatever the case, it just so happens that their theoretical framework is pretty damn excellent.

So, if you want to learn how to integrate observations in order to forecast avalanches, you should study chapter 6, and you should study it hard. I can think of no better learning material. Yes, there are clear differences between office-based forecasting and backcountry avalanche forecasting, but chapter 6 teaches you how to approach the subject with a very professional discipline.

Which certainly won't hurt.

Conclusion
Studying mountain weather, snow metamorphism, and avalanche forecasting will help you develop a detailed mental model of the mountain environment. Studying yourself will help you understand the role your psychology plays in the choices you make. For obvious reasons, it's best to study all the subjects I've discussed here, but I'd choose to learn about myself if I could only pick one.

Sometimes people ask what motivates me to write blog posts and do research ( most of which I do in my spare time, unpaid ). I do this because I know exactly what it feels like to stare death in the face. On a few occasions it might have been my own death, but that never really bothered me all that much. I don't say this because I'm fearless; the truth is that during any such situation I was simply too scared to really think about anything other than getting out.

But it's really scary to stare someone else's death in the face. It's even more awful to feel their death slowly take you down into the darkest places you can imagine. I've been there too, and honestly, few things are worse. This is what motivates me to teach myself.

I guess that's the price of love.

I know it's not cheap.

Perception, Maps, Traps

I remember, when we could sleep on stones, now we lay together in whispers and moans—U2

I've been working on several projects for the last few years and I wanted to share some output. These findings are related to the statistical model discussed in this post. Rather than a lengthy discussion, I'm simply going to post the images with brief descriptions.

The raster content of these images is used to analyse cells of the terrain for some aspects of exposure to avalanches. Other parts of the statistical modeling rely on data pulled from custom 3D models. This includes variables such as surface area, cumulative slope angle, and terrain trap statistics.

Figure 1.1. Terrain near Paradise, Mount Rainier National Park. The Jackson Visitor Centre is near the upper centre of the image. The Tatoosh range is at the bottom. This image uses natural lighting. Full size image is available here.

Figure 1.2. Terrain near Paradise, Mount Rainier National Park. This image uses slope angle shading. Full size image is available here.

Figure 1.3. Terrain near Paradise, Mount Rainier National Park. This image uses ambient occlusion to determine line-of-sight. Line-of-sight is poorest in the dark areas, but may be relatively poorer in any area that is darker than any other area. This model does not account for trees, and is therefore not easily applicable at the micro-scale. Many dark areas are also terrain traps. Full size image is available here.

Figure 1.4. Terrain near Eldorado, North Cascades National Park. This image uses natural lighting. Full size image is available here.

Figure 1.5. Terrain near Eldorado, North Cascades National Park. This image uses slope angle shading. In addition to making it easy to see slope angles, this image makes it very easy to see areas that are convoluted. Travel is difficult in convoluted terrain, and the skiing is usually pretty bad. Full size image is available here.

Figure 1.6. Terrain near Eldorado, North Cascades National Park. This image uses ambient occlusion to determine line-of-sight. Line-of-sight is poorest in the dark areas. Have you ever looked at a contour map and wondered where you might have route-finding problems? Many dark areas are also terrain traps. Full size image is available here.

Figure 1.7. Terrain near Snoqualmie Pass. This image uses natural lighting. Full size image is available here.

Figure 1.8. Terrain near Snoqualmie Pass. This image uses slope angle shading. In addition to making it easy to see slope angles, this image makes it very easy to see areas that are convoluted. Travel is difficult in convoluted terrain, and the skiing is usually pretty bad. Full size image is available here.

Figure 1.9. Terrain near Snoqualmie Pass. This image uses ambient occlusion to determine line-of-sight. Line-of-sight is poorest in the dark areas. Many dark areas are also terrain traps. Full size image is available here.

Mountain Weather Exam

225 questions from chapter 2 of The Avalanche Handbook. Questions start with green headings and answers start with red headings. I'm not sure how long it will take to complete this exam, but I can guarantee that you will gain valuable knowledge about mountain weather if you master this material.

This chapter discusses snow formation from cloud to ground, including in-depth information on snow metamorphism and its links to avalanche formation.

Mountain Weather And Snow-Climate Types

1. Snow layering that contributes to ________ formation is a combination of _______ elements interacting with the _______?
2. What causes most destructive avalanche cycles?
3. What primary atmospheric factors contribute to avalanche formation?
4. What term describes the average weather at any place?
5. List three snow climates found in North America.
6. Snow climate is useful for specific elements of avalanche forecasting. True or False?
7. If snow climate is important, explain why. If snow climate is not important, explain why not.
8. Snow climate differs by elevation, regardless of geographic location. True or False?
9. List a key reason why snow climate should not be used to forecast avalanches.

Maritime Snow Climate

1. List the two key elements of a maritime snow climate.
2. What type of precipitation can occur at any time during winter in a maritime snow climate?
3. Snow in maritime snow climates is typically stable. True or False?
4. Describe the nature of stability or instability in a maritime snow climate.
5. Describe the rate of change to instability in a maritime snow climate.
6. List three examples of North American maritime snow climates.
7. What is the total precipitation ( in millimeters ) for maritime snow climates in North America?
8. What is the average air temperature, snow depth, and density of new snow for a maritime climate?
9. Explain the significance.
10. Avalanche formation in maritime snow climates takes place when?
11. What is the term for these avalanches?
12. These avalanches involve snow near the surface? True or False?
13. What is the term for this type of instability?
14. List two effects of rain related to avalanche formation.
15. Persistent structural weakness are common in maritime snow climates. True or False?
16. If true, explain. If false, explain.
17. What type of observations are critical for avalanche forecasting in a maritime snow climate?

Continental Snow Climate

1. List the three key elements of a continental snow climate.
2. Describe the depth of the snowpack in a continental snow climate.
3. Snow in continental snow climates is typically stable. True or False?
4. If true, explain. If false, explain.
5. Describe the nature of stability or instability in a continental snow climate.
6. Describe the rate of change to instability in a continental snow climate.
7. List three examples of North American continental snow climates.
8. What is the total precipitation ( in millimeters ) for continental snow climates in North America?
9. What is the average air temperature, snow depth, and density of new snow for a continental climate?
10. Explain the significance.
11. Describe the rate of change to instability in a continental snow climate.
12. Avalanche formation in continental snow climates takes place when?
13. What is the term for these avalanches?
14. These avalanches involve snow near the surface? True or False?
15. What is the term for this type of instability?
16. What is a distinguishing feature of avalanches in a continental snow climate?
17. List two weather factors that affect continental snowpacks and how they contribute to avalanche formation.

Transitional Snow Climate

1. List the two key elements of a transitional snow climate.
2. Snow in transitional snow climates is typically stable. True or False?
3. If true, explain. If false, explain.
4. Describe the nature of stability or instability in a transitional snow climate.
5. List three examples of North American transitional snow climates.
6. What is the total precipitation ( in millimeters ) for transitional snow climates in North America?
7. What is the average air temperature, snow depth, and density of new snow for a transitional climate?
8. Explain the significance.
9. Describe the rate of change to instability in a transitional snow climate.
10. Avalanche formation in transitional snow climates takes place when?
11. What is the term for these avalanches?

Mountain Wind And Precipitation

1. Wind ________ and ________ influences precipitation patterns.
2. Speaking very generally, upon what do those two variables depend?
3. What is the most important variable for determining wind speed and direction in mountainous terrain.
4. What is the most important variable for determining the amount and pattern of snowfall in mountainous terrain.
5. What is the standard atmospheric pressure at sea level? ( In millibars. )
6. What force slows the wind at the Earth's surface?
7. At the 700-mb level, what controls wind speed and direction?
8. Where is free-air found?
9. Compare differences in airflow at 500-mb to that at the Earth's surface.
10. Why is this important?
11. 9000m elevation has an approximate air pressure of ________mb.
12. 6000m elevation has an approximate air pressure of ________mb.
13. 3000m elevation has an approximate air pressure of ________mb.
14. Unlike free air wind speed, ground-based wind-speed sensors provide measurements of air influenced by ________?
15. Maritime air is warmer than continental air. True or False?
16. Explain what can happen when a mountain range separates a maritime air mass from a continental air mass.
17. The vertical component of the wind affects these three components of precipitation.
18. Rate of precipitation is proportional to ________?
19. With respect to what you might see in the sky, upward motion of air causes what?
20. With respect to what you might see in the sky, downward motion of air causes what?
21. Describe what happens when moisture-laden air is forced up and across mountains.
22. Provide a definition for the average lapse rate.
23. Provide a typical value for the average lapse rate.
24. Cold air is less dense than warm air. True or False?
25. Explain.
26. Provide a three word flow chart of what causes precipitation.
27. What determines the moisture carrying capacity of air before condensation?
28. This means ________ air carries more water than ________ air.
29. In simple terms ( two words, an expression familiar to most people ), what might happen if a parcel of warm, moist air is forced over a mountain barrier during winter?
30. Condensation occurs as water droplets form around what?
31. The ________ at which air rises, the amount of ________ it contains, and its initial ________ are critical for determining the amount of ________.
32. Explain two separate scenarios for the above question in general terms and predict the general quantity of precipitation for cold/dry and warm/moist air masses.
33. List in order of importance the four mechanisms that cause air to rise.
34. Describe how each mechanism contributes to lifting.
35. Describe the vertical wind speed, rate of precipitation, duration of precipitation, and horizontal scale for each lifting type.
36. List the two key mechanisms with respect to winter precipitation.
37. All these elements act separately. True or False?
38. Explain.

Air Motion Around Pressure Centers

1. Define cyclone in simple terms.
2. Define anticyclone in simple terms.
3. Describe convergence.
4. What happens to air as a result?
5. What happens to the horizontal surface area of the air across the center of a low pressure area?
6. Why is this important?
7. Describe divergence.
8. What happens to air as a result?
9. What happens to the horizontal surface area of the air across the boundaries of a high pressure area?
10. Why is this important?

Frontal Lifting

1. What is a front?
2. Does lifting always occur over front?
3. List three types of fronts.
4. The boundary of a front always slopes ________ over ________ air.
5. What is the gradient of a typical warm front?
6. What is the gradient of a typical cold front?
7. Describe the precipitation intensity and duration associated with each type of front.
8. Describe the mechanism for lifting that occurs when a warm front passes.
9. Describe the mechanism for lifting that occurs when a cold front passes.
10. What influence might a mountain have on warm front lifting?
11. Why is precipitation more widespread with passage of a warm front than with passage of a cold front?

Orographic Lifting

1. Describe the process by which orographic lifting occurs.
2. The vertical component of velocity is a significant fraction of what value?
3. With respect to air, what is the result of orographic processes?
4. Why is this important?
5. Orographic lifting is ________ to ________ times stronger than frontal lifting and convergence.
6. What is an appropriate range of precipitation totals to expect from orographic lifting.
7. What terrain factor can increase orographic lifting relative to wind?
8. What wind factor can increase orographic lifting relative to terrain?
9. When do maximum orographic effects occur?
10. Explain.

Convection

1. Describe the process by which convection occurs.
2. Convection is a wide area effect. True or False?
3. In what snow climate and during what season is convection important?

Quantitative Precipitation Forecasts

1. What information does a quantitative precipitation forecast try to communicate?
2. Who produces this type of forecast?
3. What wind variable is the key factor?
4. Prediction of precipitation amounts is subject to a higher rates of error than wind and temperature. True or False?
5. Precipitation amounts are normally forecast at what scale?
6. What is the size of this scale?
7. Avalanche forecasting requires quantification of precipitation at what scale?
8. What is the size of this scale?
9. What is the primary model used by avalanche forecasters to predict precipitation for mountainous terrain?
10. Explain why this model is chosen relative to the size of the synoptic, meso, and micro scales.

Orographic Precipitation Models

1. What is the key assumption of an orographic precipitation model?
2. An air mass forms over the ocean and moves west across three mountain ranges. Describe each snow climate and amounts and expected quantity ( in general terms ) of precipitation.
3. Why does precipitation increase or decrease when an air mass crosses three mountain ranges?
4. Name two or three key data items required by an orographic precipitation model?
5. How are these data acquired?
6. How is duration of precipitation forecast?
7. Describe the three key local effects with respect to mountain-precipitation forecasting.
8. Why might snowfall increase at higher elevations?
9. Why might snowfall decrease at lower elevations?

Local Wind Flow Over Mountain Terrain

1. Wind ________ and ________ are considered essential inputs for modern forecasting.
2. Describe the most important reason why local wind speed and direction is important for backcountry travel.
3. Relative to terrain, why does wind speed generally increase with height?
4. Snowfall is generally greater on which side of a mountain?
5. List two reasons why.
6. Snow is ________ where wind ________.
7. Snow is ________ where wind ________.
8. What causes acceleration of wind?
9. Describe wind flow quality during acceleration?
10. Describe wind flow quality during deceleration?
11. Describe a terrain feature that increases turbulence.
12. With respect to wind direction, describe one effect of turbulence associated specifically with deceleration on the leeward side of a ridges.
13. What is the result?
14. Minor changes in slope angle have a significant affect on the character and areal distribution of wind deposited snow. True or False?
15. Describe a wind effect that might produce cross-loading.
16. What conditions are necessary to form a foehn / chinook wind?
17. What is the main feature of a foehn wind?
18. What snowpack element might be formed during passage of a foehn wind?

Blowing And Drifting Snow

1. Can avalanches occur from loading when snow is not falling from the clouds?
2. If so, explain. If not, explain.
3. What is threshold wind speed?
4. List three factors ( weather or snow ) that affect threshold wind speed.
5. What is threshold wind speed for loose snow?
6. What is threshold wind speed for bonded snow?
7. What are the three modes of transport for wind-redistributed snow?
8. ________ occurs at what height?
9. ________ occurs at what height?
10. ________ occurs at what height?
11. The majority of snow transport occurs at what height?
12. What often happens to snow particle size during wind transport?
13. Describe the importance or unimportance of any changes to snow particle size that occur as a result of wind transport.
14. What is an obvious sign of wind drifting on an otherwise clear day?
15. Describe snow distribution in the mountains.
16. List three terrain elements that influence snow distribution.
17. How might snow distribution during winter affect wind-deposition?
18. What is the minimum change-of-slope angle necessary to alter development of snow drifts?
19. Why is this important?

Lee Slope Deposition

1. Where are cornices often found?
2. How do cornices form?
3. What snowpack element is often found below a cornice?
4. Is this snowpack element important?
5. Describe the density of snow found in cornices.
6. List a reason why this might be important.
7. List three important features of cornices with respect to avalanche formation.

Heat Exchange At The Snow Surface

1. List three methods by which heat exchange occurs at the snow surface.
2. Describe each method.
3. Describe one possible effect of heat exchange at the snow surface.
4. How might new snowfall warm or cool the snow surface?
5. What might happen when a temperature difference exists between the snow surface and new precipitation?

Penetration Of Heat Into Alpine Snow

1. List the two primary mechanisms by which heat is transferred within snowpack.
2. Describe each.
3. What is the primary heat transfer mechanism in low density snow?
4. What is the primary heat transfer mechanism in high density snow?
5. Heat transfer through low density snow is more or less efficient as temperature decreases?
6. Why is this important?
7. Heat transfer in alpine snow is very rapid. True or False?
8. Why is heat transfer important?

Interaction Of Radiation With The Snow Cover

1. List the two key types of radiation that affect snow surface temperature.
2. What is the source of each?
3. Does radiation deeply penetrate the snowpack?
4. In general, how much shortwave radiation is reflected by dry snow and wet snow?
5. For fresh, fine-grained snow, how much solar radiation remains after 10 centimeters of depth?
6. Solar radiation can heat or cool the snowpack. True or False?
7. Which matters more, type of radiation or balance of radiation.
8. Explain.
9. Describe what happens to a south facing slope on a clear day during mid-winter.
10. Describe what happens to a north facing slope on a clear day during mid-winter.
11. With respect to radiation, what might happen during a clear night?
12. With respect to radiation, what might happen during a cloudy day?
13. Why is long wave radiation loss important?

Temperature Inversions

1. Describe a temperature inversion.
2. What is the typical cause of a temperature inversion?
3. Under what circumstances might a temperature inversion be important?

Mountain Weather And Snow-Climate Types

1. Snow layering that contributes to avalanche formation is a combination of weather elements interacting with the snowpack?
2. Direct loading of snow from synoptic scale weather events.
3. Precipitation patterns and intensity, wind direction and speed, sensible heat, and radiational heating and cooling of the snow.
4. Climate
5. Maritime, Transitional, Continental
6. False.
7. Not Important. Avalanche prediction is dynamic and highly time-dependent, regardless of snow climate.
8. True
9. Any snow climate may have some characteristics of other snow climates.

Maritime Snow Climate

1. Warm temperatures and heavy snowfall.
2. Rain
3. True
4. Changes to instability are rapid and frequent.
5. Coast Range ( British Columbia ), Cascade Range ( Washington State), Sierra Nevada ( California ).
6. 1280 millimeters
7. -1.3 degrees Celsius, 190 centimeters, 120 kilograms / cubic meter.
8. Deep snowpacks are better insulated against environmental effects. High temperatures quickly reduce instability in new snow and reduce magnitude of temperature gradient.
9. During and immediately after storms.
10. Direct-action avalanches.
11. True
12. Temporary instability, surface instability, new snow instability, storm snow instability.
13. Heavy rain loads the snow and can contribute to formation of ice crusts.
14. False
15. Warmer temperatures and deeper snowpacks promote metamorphism and bond formation by heat and overburden.
16. Weather Observations

Continental Snow Climate

1. Low snowfall, cold temperatures, location considerably inland from coastal areas.
2. Shallow
3. False
4. Snowpack in continental climates is typically unstable because of structural weaknesses induced by shallow snowpacks and cold temperatures.
5. Mostly persistent instabilities, new snow instabilities are secondary.
6. Instability is slow to change because of cold temperatures and often persists through entire season.
7. Brooks Range ( Alaska ), Canadian Rockies, American Rockies.
8. 550 millimeters
9. -7.3 degrees Celsius, 110 centimeters, 70 kilograms / cubic meter.
10. This produces a shallow snowpack subject to environmental effects. Cold temperatures help instability form and persist.
11. Slow. Instability persists for long periods, often for entire season.
12. Avalanches occur at all times but often in nice weather long after a storm passes.
13. Delayed action avalanches.
14. False
15. Persistent instability, deep instability.
16. Avalanches tend to involve old layers of snow.
17. Low snowfall leads to thin snowpacks. Cold temperatures create large magnitude temperature gradients that weaken the snowpack. Clear air drifting loads slopes.

Transitional Snow Climate

1. High snowfall and cool temperatures.
2. True
3. While snow in transitional climate is often stable, transitional snow climates are subject to frequent new snow instabilities and persistent instabilities buried in the snowpack.
4. New snow instability, some persistent instability.
5. Columbia Mountains ( British Columbia ), Wasatch Mountains ( Utah ), Madison Range ( Montana )
6. 850 millimeters
7. -4.7 degrees Celsius, 170 centimeters, 90 kilograms / cubic meter.
8. Lots of snow and deep snowpacks provide some insulation against environment effects. However, cooler temperatures allow deep instabilities to persist. In general, snowpack is stronger than continental but may be weaker in places than maritime.
9. Slow to change in the early season, quick to change later in the season. New snow instabilities vanish relatively quickly; persistent instabilities often last entire season.
10. During storms, after storms, and long after storms.
11. Direct action and delayed action avalanches.

Mountain Wind And Precipitation

1. Wind speed and direction influences precipitation patterns.
2. Wind speed and direction depend on the balance of forces in the atmosphere.
3. Horizontal component of wind velocity.
4. Vertical component of wind velocity.
5. 1013 ( 1000 is acceptable. )
6. Friction
7. Atmospheric pressure differences, frictional forces, and Coriolis force.
8. Free air wind is located several hundred meters above rough mountain topography.
9. Air flow at 500-mb is parallel to pressure contours. Airflow at the Earth's surface blows across pressure contours.
10. In high mountain terrain, wind blows toward lower pressure. This must be understood if you wish to predict wind direction and speed.
11. 9000m elevation has an approximate air pressure of 300 mb.
12. 6000m elevation has an approximate air pressure of 500 mb.
13. 3000m elevation has an approximate air pressure of 700 mb.
14. Friction induced by air motion across rough terrain features.
15. True
16. Free air winds might blow in the opposite direction of surface pressure winds.
17. Quantity, rate, and duration.
18. The vertical component of wind velocity.
19. Cloud formation and precipitation.
20. Cloud dissipation and clearing.
21. Temperature decreases with height due to expansion of the air mass. The air mass cools as it expands, leading to condensation and cloud formation. Precipitation occurs when the air cannot hold moisture because of temperature decreases.
22. Reduction in air temperature with increasing altitude.
23. 1 degree Celsius / 100 meters or 6.5 degrees Celsius per 1,000 meters.
24. False
25. Cold air is denser than warmer air. This is why it has higher pressure.
26. Lifting, expansion, condensation; rising, cooling, condensation; any three correct terms are acceptable.
27. Temperature
28. This means warmer air carries more water than cooler air.
29. Snow storm.
30. Condensation nuclei.
31. The rate at which air rises, the amount of moisture it contains, and its initial temperature are critical for determining the amount of precipitation.
32. Cold, dry air does not rise; no precipitation is the result. Warm, moist air rises quickly; heavy precipitation is the result.
33. Orographic lifting, frontal lifting, convergence, convection.
34. Description of lifting mechanisms:
    
    • Orographic. This mechanism involves motion of air across mountains with lifting occurring as a result of wind intersecting with mountain barriers and steep terrain.
    • Frontal. This mechanism involves motion of warm air rising over cold air or cold air displacing warm air, resulting in lifting.
    • Convergence. This mechanism involves air moving toward a low pressure area and being lifted through displacement.
    • Convective. This mechanism involves lifting that occurs when air is warmed at the Earth's surface.
35. Description of lifting parameters:
    
    • Orographic. ~1 centimeter / second - 2 meters / second, 1-5 millimeters per hour, up to tens of hours, 10-100 kilometers.
    • Frontal. ~1 centimeter / second - 20 centimeters / second, ~1-10 millimeters per hour, up to tens of hours, 100 kilometers for width and 1000 kilometers for length.
    • Convergence. ~1 centimeter / second - 10 centimeters / second, up to 2 millimeters per hour, tens of hours to several days, 1000 kilometers.
    • Convective. ~1 centimeter / second - 10 centimeters / second, ~1-30 millimeters per hour, minutes to hours, 0.1 to 10 kilometers.
36. Orograph lifting, frontal lifting.
37. True
38. Most of these mechanisms operate at the same time but orographic and frontal lifting have the strongest effect and therefore are the key factors for mountain precipitation.

Air Motion Around Pressure Centers

1. A low pressure center.
2. A high pressure center.
3. Convergence involves air motion toward a low pressure center. As air moves toward the low pressure center, existing air is displaced upward ( lifted ).
4. Lifting.
5. The horizontal surface area decreases. This causes displacement as air is drawn inward. Lifting is the result.
6. This results in cloud formation over a large area and widespread precipitation over any mountainous terrain near the low pressure center.
7. Divergence involves air motion outward from a high pressure center. As air moves outward, it sinks, causing clearing.
8. The air sinks.
9. It increases.
10. This results in clearing over any mountainous terrain near the high pressure center.

Frontal Lifting

1. A boundary between two air masses.
2. Yes.
3. Warm, Cold, Occluded, Stationary
4. The boundary of a front always slopes warm over cold air.
5. 1:100
6. 1:25
7. Description of precipitation intensity:
   
   • Warm Front. Steady, long-lasting ( up to 18 hours or more ), widespread across front.
   • Cold Front. Intense, short ( 4-6 hours ), oriented parallel to front.
8. Warm air rises up over the cold air.
9. Cold air flows underneath the warm air, displacing the warmer air and forcing it upward.
10. Mountains increase lifting associated with a warm front.
11. Slope differences. A warm front has a gradient of 1:100; a cold front has a gradient of 1:25. Therefore a cold front is narrow and a warm front is wide.

Orographic Lifting

1. Orographic lifting occurs when air is forced over mountain barrier. Up is the only possible direction of motion.
2. Horizontal wind speed.
3. Lifting
4. Lifting results in expansion and cooling. Cloud formation and precipitation follow soon thereafter.
5. Orographic lifting is 10 to 100 times stronger than frontal lifting and convergence.
6. 50-70%
7. Steepness of terrain.
8. Directness of wind strike angle
9. When strong wind blows perpendicular to steep terrain.
10. Wind blowing perpendicular to steep terrain is expected to produce the most vertical velocity and therefore the most lifting.

Convection

1. Convection occurs when air is warmed near the Earth's surface.
2. False
3. Convection is important during summer in continental snow climates.

Quantitative Precipitation Forecasts

1. Forecast the quantity of precipitation. Quantity = quantitative.
2. Avalanche forecasters, mountain weather forecasters.
3. Vertical component of wind velocity.
4. True.
5. Synoptic
6. 1000km
7. Meso or micro.
8. 1-100km
9. Orographic Precipitation Model
10. Orographic precipitation models work at the meso and micro scale. Synoptic scale predictions are too vague for meso-scale forecasting.

Orographic Precipitation Models

1. Precipitation is produced at a rate that is directly proportional to the rate at which air is being lifted.
2. Maritime, Transitional, Continental. Very High Quantity, High Quantity, Low Quantity.
3. Precipitation decreases because each mountain range results in a storm that decreases the amount of moisture in the air mass.
4. Wind speed, wind direction, moisture content, air temperature, lapse rate, thickness and width of air mass.
5. From upper air soundings and standard forecast products.
6. By estimating width of the moist layer and wind speed
7. Topographic Convergence, Orographic Convergence, Valley Channeling
8. Orographic effects enhance precipitation at higher elevations.
9. Slow moving air mass, in conjunction with low freezing levels, produces most of its precipitation at lower elevations.

Local Wind Flow Over Mountain Terrain

1. Wind speed and direction are considered essential inputs for modern forecasting.
2. To determine if/when/where wind loading might occur.
3. Orographic effects.
4. Windward
5. Lifting is highest on windward side and a lot of precipitation occurs as a result, leaving less moisture available for precipitation on the lee side.
6. Snow is lifted where wind accelerates.
7. Snow is deposited where wind decelerates.
8. Vertical compression of air.
9. Laminar, Smooth, Connected
10. Turbulent, Separated, Reversed
11. Sharp ridges.
12. Reversal of flow.
13. Cornice formation.
14. True
15. Valley/Canyon Wind, wind across slopes
16. Large-scale, low-pressure area in the lee side of mountain range.
17. Intense, warm flow.
18. A crust.

Blowing And Drifting Snow

1. Yes
2. Wind can transport snow. This causes heavy loading on already unstable slopes or heavy loading that destabilizes a previous stable slope.
3. The wind speed required to create blowing snow for a given set of conditions.
4. Humidity, temperature, density, time since deposition.
5. 5 meters / second
6. 25 meters / second
7. Rolling, Saltation, Turbulent Suspension
8. Rolling occurs between 0-1 millimeters.
9. Saltation occurs between 1-10 centimeters.
10. Turbulent suspension occurs between 10-100 meters.
11. The lowest meter above the surface.
12. The particles are shattered into tiny fragments.
13. This is important because it leads to formation of dense, heavy wind slab, often on already unstable slopes.
14. Blowing snow visible at any location.
15. Uneven, chaotic, variable.
16. Gullies, ridges, vegetation, cols, notches, gully walls.
17. As small features are filled in with snow, more snow is available for distribution elsewhere.
18. 10 degrees.
19. Safe travel requires the ability to assess the influence small scale features have on avalanche formation.

Lee Slope Deposition

1. Ridges
2. Wind flow becomes turbulent during deceleration. This causes reversal of flow and vortex formation.
3. Wind slab.
4. Yes, wind slab is often loaded onto already unstable slopes.
5. Very high, up to 500kg / cubic meter.
6. Heavy cornices make great avalanche triggers.
7. Cornices provide a method to assess wind direction, steep lee area below cornice is prime real estate for unstable slabs, collapse of cornice leads to avalanches or injuries.

Heat Exchange At The Snow Surface

1. Convection, Conduction, Radiation
2. Description of each method:
   
   • Convection. Heat is transferred through air.
   • Conduction. Heat is transferred through bonds between existing ice particles or between existing ice particles and new snow.
   • Radiation. Heat is transferred through incoming or outgoing radiation.
3. Weakening of snow surface. Crust formation.
4. Colder snow on warmer surface, warmer snow on a colder surface.
5. Poor bonding because of temperature mismatch.

Penetration Of Heat Into Alpine Snow

1. Vapor diffusion through air space in pores or conduction through individual ice bonds.
2. Description of each:
   
   • Vapor Diffusion. Water vapor moves through the pore space from warmer areas to cooler areas, resulting in heat transfer.
   • Ice Bonds. This occurs when heat moves from warmer snow to cooler snow through connections made by ice bonds.
3. Vapor diffusion through the pore space.
4. Conduction through ice bonds.
5. Less Efficient
6. This proves vapor diffusion is responsible for heat transport through low density snow.
7. False
8. Heat transfer is the primary mechanism that controls metamorphism ( via temperature gradient ).

Interaction Of Radiation With The Snow Cover

1. Short wave and long wave radiation.
2. Short wave = sunlight. Long wave = terrestrial sources such as stored heat, water vapor, carbon dioxide.
3. No.
4. Dry snow = 90%, Wet snow = 80%.
5. Less than 10%
6. False. It can only heat the snowpack.
7. The balance of radiation.
8. The balance of short wave and long wave radiation controls heating and cooling of the snowpack and certain balances of radiation can produce a weak snowpack, i.e. lots of solar radiation input during the and long wave radiation loss at night.
9. The snowpack warms up.
10. The snowpack cools.
11. Intense cooling through loss of long wave radiation into outer space.
12. A greenhouse effect might trap short wave and long wave radiation and warm the snow, inducing instability.
13. Long wave radiation loss can create a strong temperature gradient, resulting in development/growth of facets, surface hoar, or crusts.

Temperature Inversions

1. Temperature rises with elevation.
2. Long wave radiation loss results in cooling of the snow at high elevations. This produces cold air that sinks into the valley below.
3. A temperature inversion might result in reservoirs of cold air on one side of a mountain range. Passage of a warm front over this cold air might cause rain in avalanche starting zones.