A report on Snow and Firn

Norwegian train plowing through drifted snow

Sampling the surface of a glacier. There is increasingly dense firn between surface snow and blue glacier ice.

Extratropical cyclonic snowstorm, February 24, 2007—(Click for animation.)

Firn field on the top of Säuleck, Hohe Tauern

Frontal snowsquall moving toward Boston, Massachusetts

Cold northwesterly wind over Lake Superior and Lake Michigan creating lake-effect snowfall

An early classification of snowflakes by Israel Perkins Warren

An animation of seasonal snow changes, based on satellite imagery

New York City during a 2016 blizzard, which
produced local wind gusts up to 42 mph and dropped 27.5 in of snow, breaking the city's one-day snowfall record.

Fresh snow beginning to metamorphose: The surface shows wind packing and sastrugi. In the foreground are hoar frost crystals, formed by refrozen water vapor emerging to the cold surface.

Snow drifts forming around downwind obstructions

Snowmelt-induced flooding of the Red River of the North in 1997

Snow pit on the surface of a glacier, profiling snow properties where the snow becomes increasingly dense with depth as it metamorphoses towards ice

Snowfall and snowmelt are parts of the Earth's water cycle.

Traffic stranded in a 2011 Chicago snowstorm.

Winter conditions on Ontario Highway 401 in Toronto due to a snowsquall.

Satellite view of the Indus River, showing snow in the Himalayas, which feeds it, and agricultural areas in Pakistan that draw on it for irrigation.

Extreme snow accumulation on building roofs

Icings resulting from meltwater at the bottom of the snow pack on the roof, flowing and refreezing at the eave as icicles and from leaking into the wall via an ice dam.

Algae, Chlamydomonas nivalis, that thrive in snow form red areas in the suncups on this snow surface

Arctic fox, a predator of smaller animals that live beneath the snow

Trucks plowing snow on a highway in Missouri

Airport snow-clearing operations include plowing and brushing

Bivouac of Napoleon's Grande Armée, during the winter retreat from Moscow

Finnish ski troops during the invasion of Finland by the Soviet Union

Army vehicles coping with snow during the Battle of the Bulge of World War II.

Norwegian military preparations during the 2009 Cold Response exercise

Navy SEALs training for winter warfare at Mammoth Mountain, California.

Worldwide occurrence of snowfall. Snow at reference above sea level (meters):Below 500: annually.
Below 500: annually, but not in all of its territory.
500: above annually, below occasionally.
Above 500: annually.
Above 2,000: annually.
Any elevation: none.

Firn (from Swiss German firn "last year's", cognate with before) is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé.

- Firn

After deposition, snow progresses on one of two paths that determine its fate, either ablation (mostly by melting) or transitioning from firn (multi-year snow) into glacier ice.

- Snow

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Névé

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Névé is a young, granular type of snow which has been partially melted, refrozen and compacted, yet precedes the form of ice.

Névé that survives a full season of ablation turns into firn, which is both older and slightly denser.