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.

Interesting

There is always the promise of an early winter. To that end, I recently ran across a fascinating article about intuitive thinking, and I wanted to share it. It's a must read for anyone who deals snow ( or people ).

http://edge.org/conversation/the-marvels-and-flaws-of-intuitive-thinking&from=admin

Happy Trails!

Well it's about that time of year. Time for me to go off on some big spring ski trips, and time to put the blog on hiatus for the summer. Thanks for reading again this year, and I wish everyone a safe, happy summer. Expect new posts again at the start of November.

Best,

CookieMonster

Be Fucking Careful!

If you live in Washington State, now is a very good time to be very fucking careful. There have been a rash of incidents over the last week, and there are signs of deep instability lurking below the winter snowpack in some areas.

• Avalanche Kills Leavenworth Man
• Close call on the Funnelater ( which is a fun line in stable conditions ).
• Buried Monsters Near Crystal Mountain

Deep instabilities are not typically found in the maritime snowpack we have here Washington State; this means that terrain that is usually safe might be very dangerous. Now is a good time for snowpack observations. To this point, the report from Crystal Mountain cited a Q1 shear at 48" below surface. The fracture was described as "like a filing cabinet", which implies a clean, rapid failure.

This is a crystal clear sign of snowpack instability.

It is not possible to manage the risk associated with deep instabilities due to wide variances in snowpack structure and the associated fluctuations in the energy required for avalanche formation. Deep avalanches are always large and unsurvivable.

As always, make decisions that strike a balance between awareness and uncertainty.

Just For Fun

The Scientific Method

It's been a slow winter here in Washington, with a lot of rain, and not a lot of snow. This means that avalanche danger has been low for a long time, and it's easy to get out of the avalanche safety habit, especially if your avalanche safety habits are inconsistent in the first place.

What forms the basis of our avalanche safety habits?

On Monday I skiied Chair Peak with two local characters. Had an incredibly fun day out and about in the snow. At one point during the day, one of my ski partners asked me if I had ever thought about teaching avalanche education courses. Yes, I've thought about it. But, unfortunately, while I am allegedly qualified to teach avalanche courses, I don't have enough free time.

But it got me thinking. What would I even teach?

I would teach the scientific method, because it's what I use, and based on my current understanding of avalanche safety, the scientific method is the only realistic approach. But I wouldn't start by assuming that my students couldn't learn. Avalanche safety is a blend of complex sciences, and yes, there is a lot of complicated material. That said, learning how to approach the challenge of avalanche safety is the single most important thing you can ever learn about avalanche safety.

The scientific method provides a fantastically simple framework for teaching avalanche safety, and the primary observation categories are already determined: terrain, weather, snowpack, and humans. You start out with nothing and gradually collect information. This information helps you form inferences that eventually lead you to a conclusion. These conclusions tell you where and when to travel. Yes, as with all forms of science, it is incredibly important to avoid bias.

It really comes down to learning how to conduct observations that tell you whether or not it's safe to travel at a specific time and place. The where and when of it, if you will. The Avalanche Handbook clearly states that applying the scientific method is a good first step. If I taught avalanche classes, I wouldn't tell my students that avalanche safety is complicated and difficult, I would tell them that avalanche safety involves learning how to apply the scientific method to the problem. In short, the scientific method of avalanche safety involves observations, inferences, and conclusions that help us decide.

Avalanche safety is all about where and when can I travel based on the available data? Much of what we refer to as safety rituals or good habits really refers to the consistency with which we apply the scientific method to the problem. All the huzz about human factors just refers to the avoidance of bias in order to ensure that what we do is actually science.

Scientists have to avoid bias or their work isn't scientific. I know how this feels, because there have been days when I've stared at data on my computer screen, wishing that I could find a way for the data to provide the conclusion that I wanted it to provide.

The problem is that wishes and wants aren't science, and in the backcountry, they'll get you killed.

Further Reading:

• The Scientific Method ( You won't get very far before the subject of human factors is raised. )
• Elements of Backcountry Avalanche Forecasting ( A blog post I wrote in late 2009. )
• The Science Behind Wind Loading
• The Science Behind Snowpack Observations
• The Science Behind Terrain Observations
• The Science Behind Weather Observations
• The Science Behind Human Observations
• The Science Behind Perception of Instability

Addendum
The following is an excerpt from my contribution to an article in The Avalanche Review. This article discussed the relationship between large avalanche cycles and backcountry avalanche forecasting. You'll see that the discussion is centred around the scientific answer to the question how does an avalanche cycle change instability in the short, medium, and long-term.

The size of the forecast region is the most important factor, with precise answers only available for very small areas. However, even for small areas, the chaotic interaction between terrain and weather makes it difficult to predict the effects of widespread avalanching on future snowpack instability. The following scenario, which is just one possibility out of many, hints at the overall complexity of this forecasting problem.

Instability will persist when a bed surface composed of faceted crystals is immediately reloaded during a storm. On the other hand, future snowpack instability on that slope will be very different if the faceted crystals exposed by avalanching are subjected to multiple melt/freeze cycles prior to the next storm. Melt/freeze activity is often limited by aspect, so it is possible for the faceting process to continue on cold aspects, while faceted crystals on warm aspects undergo rounding as a result of melt/freeze metamorphism. In this highly general scenario, the weather builds new patterns of snowpack instability that are difficult to uncover without careful observations.

Therefore, for most recreational skiers, knowledge of a recent avalanche cycle is a very general and imprecise piece of information. General information often has a dangerous and unwarranted influence on individual or group beliefs about the presence of instability and its parameters. Without abundant information, expert knowledge, and significant experience ( Randy and Nick provide great examples ), a recent avalanche cycle should not exert undue influence on recreational travel choices and decision-making at any operational scale. More than anything, incremental changes to the snowpack caused by synoptic scale weather events will alter the characteristics of the danger but won't eliminate it.

• The chaotic relationship between terrain and weather is a primary source of uncertainty.
• Incremental changes to the snowpack are a primary source of uncertainty.
• Avalanches remove weak snow from some, but not all, slopes.
• Avalanches may or may not remove all the weak snow from a specific slope.
• Use multiple sources of information to determine the likelihood of avalanche formation.
• An avalanche cycle over a large area certainly does not mean a specific slope is safe.

Proactively managing uncertainty is essential to safe decisions.