A meteorological phenomenon is a weather event which can be explained by the principles of meteorology.
Atmospheric phenomena that are monitored at meteorological stations can be divided into the following groups:
– “usual” weather phenomena that are quite common, such as rain, snow, cloudiness, etc. that can affect agricultural and social aspects of life but not in a very considerable way;
– significant weather phenomena that can destroy objects, cause deaths and impair life quality leading to current interruptions, traffic jams, etc.
Some of these can also delay or even cancel sport competitions.
An avalanche is a rapid flow of snow down a slope, from either natural triggers or human activity. Typically occurring in mountainous terrain, an avalanche can mix air and water with the descending snow.
A blizzard is a severe storm condition characterized by low temperatures, strong winds, and heavy snow. By definition, the difference between blizzard and a snowstorm is the strength of the wind. Ground blizzards are a variation of the traditional blizzard, in that ground blizzards require high winds to stir up snow that has already fallen, rather than fresh snowfall. Regardless of the variety of blizzard, they can bring near-whiteout conditions, which restrict visibility to near zero. Blizzards have a negative impact on local economies and for days at a time can paralyze regions where snowfall is unusual or rare.
Snowstorms are storms where large amounts of snow fall. Snow is less dense than liquid water, by a factor of approximately 10 at temperatures slightly below freezing, and even more at much colder temperatures. Therefore, an amount of water that would produce 0.8 in. (2 cm.) of rain could produce at least 8 in (20 cm) of snow. Two inches of snow (5 cm.) is enough to create serious disruptions to traffic and transport (because of the difficulty to drive and maneuver the school buses on slick roads).
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A snowdrift is a deposit of snow created by wind into a mound during snowstorms. They resemble sand dunes and are formed in a similar manner, namely, by wind moving light snow and depositing it when the wind is slowed, usually against a stationary object. Snow normally crests and slopes off toward the surface on the windward side of a large object. On the leeward side, areas near the object are a bit lower than surrounding areas, but are generally flatter.
Lightning is an atmospheric discharge of electricity accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms. In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 60,000 m/s (130,000 mph), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough to fuse silica sand into glass channels known as fulgurites which are normally hollow and can extend some distance into the ground. There are some 16 million lightning storms in the world every year.
Thunder is the sound made by lightning. Depending on the nature of the lightning and distance of the listener, thunder can range from a sharp, loud crack to a long, low rumble (brontide). The sudden increase in pressure and temperature from lightning produces rapid expansion of the air surrounding and within a bolt of lightning. In turn, this expansion of air creates a sonic shock wave which produces the sound of thunder, often referred to as a clap, crack, or peal of thunder. The distance of the lightning can be calculated by the listener depending on when the sound is heard vs.
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