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Ice & Snow

What is Snow?

Snow is precipitation in the form of ice crystals. It originates in clouds when temperatures are below the freezing point (0 degrees Celsius, or 32 degrees Fahrenheit), when water vapor in the atmosphere condenses directly into ice without going through the liquid stage. Once an ice crystal has formed, it absorbs and freezes additional water vapor from the surrounding air, growing into a snow crystal or snow pellet, which then falls to Earth. 

Scientists study ways to map global snow cover as well as ice from satellite and ways to determine the contribution of melting snow to regional water supplies. 


Image of the arctic frozen over
A view of snow and ice in the Arctic.


Common Phenomena 

Image of the earth with sea ice
It is simply frozen ocean water. It forms, grows, and melts in the ocean. Sea ice occurs in both the Arctic and Antarctic. Sea ice has a bright surface, so much of the sunlight that strikes it is reflected back into space.
Investigate SEA Ice
Satellite image showing lake effect clouds over the Great Lakes
This occurs when cold air moves across the open waters of the Great Lakes. As the cold air passes over the unfrozen and relatively warm waters of the Great Lakes, warmth and moisture are transferred into the lowest portion of the atmosphere. The air rises, clouds form and grow into a narrow band that produces 2 to 3 inches of snow per hour or more.
The Lake Effect
Image of a storm on the east coast of the united states
A nor’easter is a storm along the East Coast of North America, so called because the winds over the coastal area are typically from the northeast. During winter, the polar jet stream transports cold Arctic air southward. The difference in temperature between the warm air over the water and cold Arctic air over the land is the fuel that feeds Nor’easters.
What is a Nor'easter?
Image of snowstripes
Snowflakes form when water vapor travels through the air and condenses on a particle. Snow is not simply a frozen droplet of water falling from a cloud. What makes a snowflake different is that it forms slowly, and that it grows in the cloud. Snow cover extent in the U.S. and the rest of the Northern Hemisphere is mapped from satellite observations.
What is snow really?
Satellite view of water vapor over the United States
This term can encompass blizzards, blowing snow, squalls, or snow showers. Remote sensing, combined with in-situ measurements, can either make direct observations or create models on pack accumulation, heat exchange at the air-snow interface, areal extent of snow cover, heat storage within the snow pack, liquid water retention, and transmission and heat exchange at the ground-snow interface.
Blizzards, Squalls & More


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