Difference between revisions of "Category:About Snow"
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== Snow Grooming ==
== Snow Grooming ==
Revision as of 11:27, 5 February 2011
Information about snow in general - what is it, how it forms, weather patterns that bring snow, snow making, snow grooming, different types of snow and stuff.
What snow is
Snow is precipitation. If forms when water freezes on nuclei such as dust or silver iodide (or other artificial nuclei seeded into the atmosphere as cloud seeding), forming characteristic symmetric six sided crystals. Apparently no two snowflakes are identical, but I haven't looked at them all. The symmetry gives rise to one of the great questions of our age - how does one arm of a growing crystal know what is happening on the other five arms so the pattern of growth is repeated?
As a general proposition, snow will melt down to a depth of water 1/10 its depth as snow, but this depends on the moisture content of the snow. A corollary of this is that, to work out the depth of snow that has fallen, multiply the amount of precipitation recorded by 10ish. The lighter the snow, the smaller the amount of water when it melts. Generally, snow that forms in warmer temperatures and in areas of greater humidity is heavier. Light snow is the powder we all crave. A simple test is that snow that deserves the description "powder" will not cohere into a snowball when squeezed.
Snow settles and becomes compact over time, so, even without melting, the total fall for a season will be greater than the depth on the ground.
Basics on how to interpret a synoptic chart looking for key things like cold outbreaks and cutoff lows. What on earth is a 540 line and why do people talk about it? What does cold snow bearing cloud look like on a satellite image? What pet theories are then on predicting snowfalls or the season ahead? What about the future and global warming, what impact will that have on us?
Snowmaking requires a significant level of infrastructure including water storages, pump stations compressors, pipes, electricity supply, hydrants and weather stations. S.
The efficiency of snowmaking is largely driven by weather conditions. Low temperature and low humidity increase snowmaking efficiency. The combination of humidity and temperature is called the wet bulb. Generaly good snow is made below the wet bulb of -3c.
Air-water guns produce a more concentrated stream of snow, which can be more effectively directed along confined trails or accumulated in a large pile for distribution by grooming machines.
Both types of snow guns can be mounted on a tower to increase the amount of time (hang time) the water droplets are in the air, which increases the amount of snow that can be produced Under what conditions can you make snow?
There are even some home made snow guns operating in Aussie suburbs.
Main Article: cloud seeding
Groomed slopes are often called "piste" while runs that are not groomed are called "off-piste".
When a ski run is groomed, it has had a snow tractor (known as a "sno-kat", "khasborer" or "groomer") drive over the ski run to flatten it out.
The groomer generally has two main tools. The blade at the front (similar to the blade on a bulldozer) allows large amounts of snow to be positioned. The tiller on the back of the rear of the groomer contains a set of blades, followed by a rake and mats. The tiller is responsible for making the 'corduroy' surface - so named became of the parallel ridges that are formed in the snow by a groomer.
The purpose of grooming is to flatten any bumps created by traffic and remove any unseen hazards. Tasks which may be performed by the groomer are:
- Piste preparation (making runs for skiers)
- Preparation of load areas for lifts
- Movement of snow onto access trails and high traffic areas
- Flattening of mogul fields
- Snow farming (where snow if bought in from off piste areas onto runs)
- Mass movement of snow for terrain park construction
- Movement of 'whales' (piles of snow) in front of snowmakers
- Movement of snow to cover up obstacles
- Filling in drains that have become exposed.
The final result after a slope has been groomed is a super flat and smooth run free of any hazards that could affect your skiing or snowboarding. The grooming machines leave a surface that looks like corduroy, and groomed snow is sometimes referred to as corduroy.
There are a number of problems that can arise when grooming. Warm weather may mean sloppy snow that results in poor traction. This causes the tracks of the groomer to dig in and many leave indentations behind the groomer which the tiller cannot flatten out. Problems also arise when the snow 'goes off' while grooming. This results in the snow balling up on the blade and under the groomer, resulting in death cookies (balls of ice). Normally in Australia, snow is pushed back up hill to cover obstacles and freeze up, in other countries snow is moved down the hill to expose new fresh packed snow from underneath (this can only be achieved in areas of high snowfall).
Groomers may also have a 'pipe dragon' attached to them. This is essentially a tool that cuts a quarter pipe (a wall with a transition). These are used for forming quarter and half pipes in terrain park, and save many person-hours of hand shaping and maintenance of terrain park features.
Types of Snow
- Ankle Breaker: See Crust.
- Breakable: See Crust.
- Boilerplate: Ice that is so hard it is difficult to get an edge in... and is sometimes see thru (like ice in your freezer tray).
- Corduroy: The surface left after a grooming machine has finished with snow. Corduroy describes the appearance oof this snow before boarders and skiers sink their edges into it.
- Corn Snow: Usually found in the Spring, this snow is characterized by it's large, corn kernel size granules. Also known as Ego or Hero snow as it is very easy to ski on and very forgiving.
- Crud: Heavy, wet snow (although other opinions exist). The US generally refer to this as 'tracked out' powder.
- Crust: Snow that has a crust on the surface. Generally formed by light rain/mist freezing on the surface, trapping in the dry snow underneath or by wind compacting the surface layer.
- Death Cookies: Large frozen lumps of snow created by poor grooming, avalanche debris, crumbled cornices etc. Deadly when hit, and even worse when covered by a layer of new snow so they are invisible. Easily confused with dead wombats.
- Dust on Crust: Crust with a big of fresh powder on top (so you can't see what you are skiing on, but you're skiing on junky snow).
- Dry Snow: Falls at temperatures of -4 or below. Will generally squeak when walked on (like sand on a beach), and will be 'grippy' when packed.
- Ego Snow: See Corn Snow.
- Elephant Snot: Similar to wet snow but characteristic of Aussie conditions when you get nice dry snow and then it warms up and turns to the consistency of porridge.
- Freeze Dried: Snow that has a lot of moisture sucked out of it by a heavy frost. This type of snow can sometimes has similar properties to powder.
- Firm: See Ice
- Hard Pack: When natural snow becomes firmly packed by repeated grooming or continuous wind exposure. Often snow that has never melted or recrystalized.
- Heavy Snow: Normally warm fresh snow (falling at near zero degrees).
- Hero Snow: See Corn Snow.
- Horizontal Snow being blasted horizontally by a blizzard.
- Icy: Icy is a hard, glazed surface created by one or a combination of the following: freezing rain, rapid freezing temperatures or saturation from ground water seeping up into the snow and then freezing. This type of snow often has a translucent appearance.
- Machine Groomed: Loose granular snow that has been repeatedly groomed by power tillers.
- New Over: This snow is used to describe any accumulation of snow over an existing surface, for example "New over packed powder" or "New over machine groomed".
- Packed Powder: Powder snow that has been packed down up the above mentioned forces. It is no longer fluffy, but not hard snow, either.
- Powder: The product of fresh, natural snow. Cold, new, loose, fluffy dry snow that has not been compacted by skier traffic or grooming.
- Porridge: See Elephant Snot.
- Sago: Minature hail like snow that falls at temps close to freezing. Immature snow that has gone through many freeze thaw cycles in the cloud before falling. Excellent at ripping the face off poor unsuspecting skiers and boarders as they ride the chairlift with a 80km/h gale at the top.
- Sastrugi Firm (if not icy) windblown ridges.
- Sierra Cement: See Elephant Snot - term used mostly in the Sierra Nevadas in California as their snow isn't as dry as places like Colorado
- Slurpee Park: See Elephant Snot.
- Slush: Typically Spring snow that has suffered the effects of high temperatures and becomes very wet.
- Softening: Typical Spring conditions, started out rock hard, turning to slop by lunchtime.
- Spring Snow: Generally used in the same context as corn snow, but can be used to mean the full cycle of snow that occurs in Spring, ie: firm in the morning, softening to corn snow, then possibly slush.
- Wet Snow (Wet Pack): Snow that has become moist due to thaw or rainfall. Snow with a high moisture content when it fell.
- Wind Blown Pockets: Dry snow that accumulates in valleys/depressions from being blown by the wind.
- Wind Packed: Fresh snow that has been packed by the wind. Generally, this snow is dry.
- Wind Polished: Ice, in resort snow report speak.
- Yellow You don't want to know. Not to be eaten.
There are two ways of measuring slope steepness. The first is a measurement using degrees, which measures the angle of the slope in degrees from the horizontal. The second is a percentage. This is calculated using the formula 100*rise/run. Rise is the vertical change and run is the horizontal distance. A 100% slope is angled at 45 degrees.
10% is equivalent to 5.71º
20% is equivalent to 11.31º
30% is equivalent to 16.7º
40% is equivalent to 21.8º
50% is equivalent to 25.67º
75% is equivalent to 36.8º
100% is equivalent to 45º
A beginner slope is typically between 6% and 25%. Intermediate hills range from 25% to 40%, and expert is 40% plus. As you can see, hills are not as steep as you think they are.
- Cornices are steep, often overhanging snow drifts that form on the lee side of ridges. As the wind crosses the ridge it slows down, and windblown snow is deposited. The drifts formed in this way can be very deep - much deeper than surrounding snowpack. Cornices are often unstable and the lips break away and roll down hill. Sometimes the whole cornice will slide.
- Snow Angels Shapes kids (or adults) make when they lie in the snow on their back and flap their arms up and down. It makes the shape of wings in the snow and combined with the body imprint leaves the shape of an angel.
- Snow Ghosts Snow ghosts are trees covered in snow and ice shaped by wind and sun. What causes Snow ghosts? The presence of snow ghosts indicates that fog happens often at the resort.
- Bumps or Moguls are lumps in ski runs caused by the action of skiers turning. Most skilled skiers turn where there are slight terrain variations which help with unweighting. As this occurs ruts are carved by the turning skis. The ruts become terrain changes in themselves, which in turn are used for turns. This is repeated. Once the bumps and ruts are established it becomes difficult to turn anywhere else, and fields of bumps become established. One little known fact is that, until boarders came along, skiers did not produce bumps. The production of bumps was a very effective tactic to discourage boarders.
- Whiteout A whiteout happens when fog reduces contrast to the extent that you cannot tell where the snow ends and the air begins. In a bad whiteout you sometimes cannot tell if you are moving or stationary. It is disconcerting, and can be dangerous if you cannot tell how steep the slope is. If you are in a whiteout contrast and visibility improve immensely near solid objects like trees. Stick to the edges of runs.
Unusual Snow Events
Snow falls in fairly predictable places but every now and then an unusual cold front whips through and results in snow falling in the most unusual places.
- Australia : Unusual snow events in Australia
Types of Lift
- Aunty Jack Lift Alternate name for a rope tow. So named because they rip your bloody arms off, the catch cry of Aunty Jack.
- Chairlift Self explanatory. A chair suspended from a cable that carries you up the mountain. In the olden days most chairs were doubles (although there are some singles). As time, technology and loading and unloading methods advanced quad chairs arrived. Then sextuples. There are now 8 seater chairs, which operate with surprisingly little carnage at the top. There is one at Perisher.
- There are two basic types of chair:
- Fixed grip The chair travels through the loading station at the same speed as the cable.
- Detachable Chairs are clamped to the cable, but are detached as they enter the loading or unloading station. The chair travels slowly while peeople get on and off, but travels quickly for most of the ride.
- Detachables move more people than fixed grips. There are lifts that are a hybrid of these two types, such as those that use a moving carpet to accelerate riders up to the speed of a fast moving fixed grip chair.
- Combined Lifts Basically a mix between a chairlift and a gondola on a standard detachable lift. An example would be the Horse Hill Lift/Gondola at Mt Buller which consists mainly of chairs and some gondolas grouped in fours.
- Gondola Similar to a chairlift, but fully enclosed. Sitting down. Out of the wind. Quick. The happiest lift of them all. There are rumours of certain clothes optional activities during longer rides, but truly dedicated folk are concentrating on their next run.
- J-bar A drag lift where a large disc is placed between the legs which drags you up the hill. Also called Pomas, but Poma is a tradematk of the Pomalgalski Lift Co, so you should not call it a Poma unless it is a Poma. Sometimes called Cheap Thrill Lifts. I don't know why. Do not shout "Single!!" People will love you, but you will look like a goose.
- Jig Back Gondola A strange one. There are two groups of gondola cars that shuttle backward and forward, reversing direction each time. There is one of these at Seaworld on the Gold Coast. They are not much use as a means of moving people up a hill, but are sometimes used as people movers. There is one at Panorama in Canada. Cable cars are jig back lifts. There are two cars that shuttle up and down.
- Lateral Ground Transportation System What Alta, with tongue firmly planted in cheek, calls a rope tow.
- Magic Carpet A conveyor belt that takes beginners up th hill. Simple, not intimidating and effective.
- Nutcracker These are essentially rope tows, but you get pulled up by attaching a nutcracker (a belt with large metal clamp that resembles a nutcracker) to the rope. This allows you to go up very steep slopes that would be almost impossible to get up if you were just grabbing onto the rope. Nutcracker tows are the usual type of lift in the New Zealand club ski fields, there are also a number of rope tows operating in Australia , most are in backcountry areas, but there are four at the small Mt Mawson resort in Tasmania.
- Poma A disk attached to a pole that slips between your legs, also known as a 'Platter' lift. Allow it to drag you, do NOT sit down or you will fall off. Many Pomas move much faster than T-Bars and some have bends such as the International and Lakeside Pomas at Falls Creek. Be careful when riding a poma around a curve or you may be thrown off, however with a little practice you can get airborne for a second or two! Sometimes called 'J-Bars' in NSW, but this term is unheard of in Victoria. Poma is actaully the name of a company that manufactures lifts, so you may see 'Poma' on the side of a Chairlift station.
- Rope Tows The simplest lift of them all. A rope goes round and round. You grab it, and are dragged up the hill. Sometimes there are handles attached to the cable. Often it is just a cable. Crude but effective.
- T-bar A surface lift. This means that the rider remains on the surface of the snow. Also called a drag lift. The rider is dragged up the hill. A horizontal bar is tucked under the backside of the riders, and they are dragged uphill. Drag is an important concept. If you sit on a t-bar you fall off. People will laugh. T-bars are designed for two people. If, through incompetence (and I am looking at you, snowboarders), or ignorance you ride single when there is a crowded line people will laugh and hurl abuse. If you are alone shout "Single!!" and someone will probably join up. It could be the start of a beautiful friendship. At the very worst you will find that your observations about the weather and conditions are shared by a total stranger. Riding a T-Bar.
- Tram, Cablecar or Telecabine A big box containing heaps and heaps of people who are whisked uphill.
Snowdepths in Australia
Snowy Hydro have been tracking snow depths in the NSW mountains for many years. They have a snow depth chart on their web site, which allows you to call up charts for snow depths at 3 locations in various years, and to compare different years. The data for Spencers Creek most closely matches the depths in the actual resorts. It is not a perfect match.
In Victoria, the snowdepths are traditionally measured by the resorts themselves. Many years ago there were lots of accusations of inaccuracies. However with the advent of snowcams people are easily able to check the accuracy for themselves. Most resorts have an offical measuring post for natural depth (for example Hotham's is in the trees next to the road runner lift). There are also measurements taken in an area that is representative of snowmaking depth.
Snowdepths and Conditions in North America
America generally has a better and longer snow seasons than the Australian ski resorts due to their weather system and altitude of the ski resorts. Average bases can range from 2 metres deeps to a massive 10 metres deep depending on the ski region. Be warned though that even though the snow conditions are much more reliable than in Australia, they do too have bad seasons that struggle have any terrain open.
The consistent deep snow means that North American resorts often do not do much summer grooming, relying on snow depth to cover rocks, fallen trees, alders, dead mooses and other shrubbery. This means that, even with snow depths that Australian resorts can only dream of, some areas of resorts cannot open or are sketchy.
For more information about snow depth in US, visit this site. This site has an incredibly detailed analysis of snowfalls in North America spanning many years. Get daily snow condition updates at Ski trip USA
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