Snow is a fascinating phenomenon that transforms landscapes and affects various aspects of our environment. To understand when it snows, we need to delve into the conditions necessary for snow formation and explore the different characteristics of snow.
Snowflakes are accumulations of many snow crystals.
How Snow Forms
Snow forms when the atmospheric temperature is at or below freezing (0°C or 32°F). For snow to fall, moisture must be present in the atmosphere. Snowstorms also rely heavily on temperature, but not necessarily the temperature we feel on the ground. If the ground temperature is at or below freezing, the snow will reach the ground. However, the snow can still reach the ground when the ground temperature is above freezing if the conditions are just right.
In this case, snowflakes will begin to melt as they reach this higher temperature layer; the melting creates evaporative cooling, which cools the air immediately around the snowflake. This cooling slows down melting. As a general rule, though, snow will not form if the ground temperature is at least 5°C (41°F). While it can be too warm to snow, it cannot be too cold to snow. Snow can occur even at incredibly low temperatures, as long as there is some source of moisture and some way to lift or cool the air.
It is true, however, that most heavy snowfalls occur when there is relatively warm air near the ground-typically -9°C (15°F) or warmer-since warmer air can hold more water vapor. Because snow formation requires moisture, very cold but very dry areas may rarely receive snow. Antarctica's Dry Valleys, for instance, form the largest ice-free portion of the continent. The Dry Valleys are quite cold but have very low humidity, and strong winds help wick any remaining moisture from the air. As a result, this extremely cold region receives little snow.
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Snow on the Ground
Snow is an accumulation of packed ice crystals, and the condition of the snowpack determines a variety of qualities, such as color, temperature, and water equivalent. As weather conditions change, the snowpack can change as well, and this affects the characteristics of the snow.
The character of the snow surface after a snowfall depends on the original form of the crystals and on the weather conditions present when the snow fell. For example, when a snowfall is accompanied by strong winds, the snow crystals are broken into smaller fragments that can become more densely packed. After a snowfall, snow may melt or evaporate, or it may persist for long periods.
If snow persists on the ground, the texture, size, and shape of individual grains will change even while the snow temperature remains below freezing, or they may melt and refreeze over time, and will eventually become compressed by subsequent snowfalls. Over the winter season, the snowpack typically accumulates and develops a complex layered structure made up of a variety of snow grains, reflecting the weather and climate conditions prevailing at the time of deposition as well as changes within the snow cover over time.
The Colors of Snow
Generally, snow and ice present us with a uniformly white appearance. This is because visible light is white. Most all the visible light striking the snow or ice surface is reflected back without any particular preference for a single color. Most natural materials absorb some sunlight, which gives them their color. Clean snow, however, reflects most of the visible sunlight, creating a white appearance. How much sunlight the snowpack reflects to the atmosphere is characterized as snow's albedo.
Near Whistler, Canada, blooms of algae give snow a red or pink tint, called watermelon snow.
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Snow most frequently appears white, but deep snow can act as a filter, absorbing more of one color and less of another. Deep snow tends to absorb red light, reflecting the blue tints often seen in snow. However, snow may also appear blue. As light waves travel into the snow or ice, the ice grains scatter a large amount of light. If light travels over any distance, it must survive many such scattering events. That is, it must keep scattering and not be absorbed.
The observer sees the light coming back from the near surface layers after it has been scattered or bounced off other snow grains only a few times, and it still appears white. The absorption is preferential: More red light is absorbed than blue. The difference in absorption is small, but is enough that over a considerable distance, say a meter (3.3 feet) or more, photons emerging from the snow layer tend to be made up of more blue light than red light.
For instance, if you were to poke a hole in the snow and look down into the hole, you may see a bluish color. In each case, the blue light is the product of a relatively long travel path through the snow or ice. Think of the ice or snow layer as a filter. If it is only a centimeter (0.39 inches) thick, all the light makes it through, but if it is about one meter (3.3 feet) thick, mostly blue light makes it through.
Particles or organisms within the snowpack may also affect the color of the snow. Watermelon snow, for instance, appears red or pink. This coloration is caused by a form of cryophilic, or cold-loving, fresh-water algae that contain a bright red pigment. Watermelon snow is most common during the summertime in high alpine areas as well as along coastal polar regions. Although this snow may look candy-colored, it is not wise to eat it.
Blood Falls, in Antarctica's Taylor Glacier, also has red snow, but for a different reason. There, the deep red color is caused by saltwater leaking from an ancient reservoir under the glacier. This water is rich in a form of iron that oxidizes when it comes into contact with the atmosphere, producing a bright red waterfall.
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A coating of dust darkens this snowpack in the Rocky Mountains and hastens its melt.
Dark-colored particles such as dust and soot can change snow's appearance and because they absorb more sunlight, hasten snow's retreat. Studies in the southwestern Colorado San Juan Mountains have shown that a layer of dust at the surface of a snowpack can shorten the duration of snow cover anywhere from 21 to 51 days. In contrast, an air temperature increase of 2 to 4°C (4 to 7°F) would shorten snow cover duration by only 5 to 18 days. Dust layers can become buried in the snowpack as new storms add clean snow on top, but these dust layers will emerge as the top layers melt away.
Snow and Sound
The characteristics and age of snow can affect how sound waves travel, dampening them in some cases or enhancing them in others. For instance, people often notice how sound changes after a fresh snowfall. When the ground has a thick layer of fresh, fluffy snow, sound waves are readily absorbed into the snow surface, dampening sound.
However, time and weather conditions may change the snow surface. If the surface melts and refreezes, the snow becomes smooth and hard. Then the surface will help reflect sound waves. Sounds may seem clearer and travel farther under these circumstances.
Snow may also crunch and creak. A layer of snow is made up of many tiny ice grains surrounded by air, and when you step on it, you compress the grains. As the snow compresses, the ice grains rub against each other. This creates friction or resistance; the lower the temperature, the greater the friction between the grains of ice. The sudden squashing of the snow at lower temperatures produces the familiar crunching sound. At higher temperatures, closer to melting, this friction is reduced to the point where the sliding of the grains against each other produces little or no noise.
It is difficult to say at what temperature the snow starts to crunch, but the colder the snow, the louder the crunch.
Snow Depth and Temperature
A fox makes a den out of a snowbank in Alaska.
The snow surface temperature is controlled by the air temperature above. The colder the air above, the colder the snow layers near the surface will be, especially within the top 30 to 45 centimeters (12 to 18 inches). Snow near the ground in deeper snowpack is warmer because it is close to the warm ground. The ground is relatively warm because the heat stored in the ground over the summer is slow to dissipate. In addition, snow is a good insulator, similar to the insulation in the ceiling of a house, and thus slows the flow of heat from the warm ground to the cold air above.
How Much Water Is in Snow?
Snow is composed of frozen water crystals, but because there is so much air surrounding each of those tiny crystals in the snowpack, most of the total volume of a snow layer is made up of air. We refer to the snow water equivalent of snow as the thickness of water that would result from melting a given layer of snow. An often-repeated assumption claims a ten-to-one ratio of snow to water, but that is not always accurate.
The water equivalent of snow is more variable than most people realize. For instance, 25 centimeters (10 inches) of fresh snow can contain as little as 0.25 centimeters (0.10 inches) of water and as much as 10 centimeters (4 inches) of water, depending on crystal structure, wind speed, temperature, and other factors. The majority of new snowfall in the United States contains a water-to-snow ratio of between 0.04 (4 percent) and 0.10 (10 percent), depending on the meteorological conditions associated with the snowfall.
Snowfall in California:
California's annual average snowfall total is 227".
Snow Report in California Ski Resorts:
Here is a summary of snow conditions in various California ski resorts:
| Resort Name | Snowfall 24h | Base Depth | Open Trails | Open Lifts |
|---|---|---|---|---|
| Bear Mountain | 0" | 18-24" | 3/26 | - |
| Bear Valley | 7" | 25" | 47/103 | 7/10 |
| Boreal Mountain Resort | 18" | 31" | 9/34 | 4/13 |
| Dodge Ridge | 0" | - | 53/71 | 8/10 |
| Heavenly | 5" | 46" | 51/111 | 15/27 |
| Kirkwood | 7" | 20-60" | -/84 | 6/13 |
| Mt. Shasta Ski Park | 35" | 35" | 44/44 | 4/6 |
| Northstar California | 0" | 21" | 42/100 | 10/20 |
| Palisades Tahoe | 0" | 23-52" | 69/288 | 22/39 |
| Sierra-at-Tahoe | 6" | 35-60" | 7/47 | 4/14 |
| Ski China Peak | 8" | 15" | 26/54 | 6/11 |
| Snow Summit | 0" | 12-18" | 3/3 | - |
| Snow Valley | 1" | 12-24" | -/32 | 1/9 |
| Soda Springs | 24" | 30" | 4/19 | 4/6 |
| June Mountain | 0" | 22" | ----- | ----- |
| Mammoth Mountain | 6" | 48-76" | ----- | ----- |
| Mountain High | 0" | 9-13" | ----- | ----- |
Popular Californian cities that experience snow in winter:
- Big Bear Lake
- Lake Arrowhead
- Frazier Park
- Mammoth Mountain
- Yosemite National Park
- Lake Tahoe
How Big Can Snowflakes Get?
A large snowflake stands out in this cluster of polycrystals.
Snowflakes are accumulations of many snow crystals. Most snowflakes are less than 1.3 centimeters (0.5 inches) across. Under certain conditions, usually requiring near-freezing temperatures, light winds, and unstable atmospheric conditions, much larger and irregular flakes can form, nearing 5 centimeters (2 inches) across. No routine measurements of snowflake dimensions are taken, so the exact size is not known.
Types of Snow
Atmospheric conditions affect how snow crystals form and what happens to them as they fall to the ground. Snow may fall as symmetrical, six-sided snowflakes, or it may fall as larger clumps of flakes. Similarly, once snow is on the ground, the snowpack may assume different qualities depending on local temperature changes, whether winds blow the snow around, or how long the snow has been on the ground. For instance, a fresh snowfall may be loose and powdery, but snow that has been on the ground throughout the winter may have dense, crusted layers caused by melting and refreezing.
Types of Snow Crystals
- Snowflakes: Single ice crystals or clusters of ice crystals that fall from a cloud.
- Hoarfrost: The deposition of ice crystals on a surface when the temperature of the surface is lower than the frost point of the surrounding air. In this process, moisture goes directly from vapor to solid, skipping the liquid phase. Hoar frost is usually composed of interlocking ice crystals, and tends to form on objects of small diameter that are freely exposed to air, such as wires, poles, tree branches, plant stems, and leaf edges.
- Rime frost: Occurs when supercooled droplets freeze and attach onto an exposed surface. The moisture comes typically comes from freezing fog or mist droplets that turn directly from a liquid state to a solid state, with calm winds.
- Graupel: Consists of snowflakes that become rounded, opaque pellets ranging from 2 to 5 millimeters (0.1 to 0.2 inches) in diameter. They form as ice crystals fall through supercooled cloud droplets, which are below freezing but remain a liquid. The cloud droplets then freeze to the crystals, forming a lumpy mass. Graupel is sometimes mistaken for hail, but tends to have a texture that is softer and more crumbly. Graupel is sometimes also called snow pellets.
- Polycrystals: Snowflakes composed of many individual ice crystals.
Types of Snowfall
- Blizzard: A violent winter storm, lasting at least three hours, which combines subfreezing temperatures and strong winds laden with blowing snow that reduces visibility to less than 0.40 kilometers (0.25 miles).
- Snowstorm: Features large amounts of snowfall.
- Snow flurry: Snow that falls for short durations and with varying intensity; flurries usually produce little accumulation.
- Snow squall: A brief, but intense snowfall that greatly reduces visibility and which is often accompanied by strong winds.
- Snowburst: A very intense shower of snow, often of short duration, that greatly restricts visibility and produces periods of rapid snow accumulation.
- Drifting snow: Snow on the ground that is blown by the wind to a height of more than 2.5 meters (8 feet) above the surface. Once it rises above that height, it becomes blowing snow.
- Blowing snow: Describes airborne snow particles raised by the wind to moderate or great heights above the ground, at a height of 2.5 meters (8 feet) or more; the horizontal visibility at eye level is generally very poor.
Types of Snow Cover
- Snow cover (snowpack): The total of all the snow and ice on the ground. It includes new snow and previous snow and ice that have not melted.
- New snow: A recent snow deposit in which the original form of the ice crystals can be recognized.
- Firn: Rounded, well-bonded snow that is older than one year and has a density greater than 550 kilograms per cubic meter, or 55 percent.
- Névé: Young, granular snow that has been partially melted, refrozen and compacted; névé that survives a full melt season is called firn. This type of snow is associated with glacier formation.
- Old snow: Indicates deposited snow whose transformation is so far advanced that the original form of the new snow crystals can no longer be recognized.
- Seasonal snow: Refers to snow that accumulates during one season or snow that lasts for only one season.
- Perennial snow: Snow that persists on the ground year after year.
- Powder snow: Dry new snow, which is composed of loose, fresh ice crystals.
Packing for winter in California:
What to pack for winter in California largely depends on where in the state you're traveling to. In cities such as Los Angeles and San Francisco, the weather is still reasonably warm and comfortable so packing clothing items such as t-shirts, dresses, jeans, and shirts are acceptable. You should still pack sweaters and cardigans though as the temperature can drop in the evenings. If you're traveling to areas in California that receive a lot of snow then the appropriate snow clothing is required. This can include snowsuits, heavy-duty and waterproof pants and tops, as well as waterproof jackets, coats, thick socks, gloves, and beanies.