Even though we don’t get much snow in Crondall (our local records and history are here), we nevertheless get asked lots of snow related questions, so we’ve tried to pull together answers to the most common ones.
Snow forms when tiny ice crystals in clouds stick together to become snowflakes. If enough crystals stick together, they’ll become heavy enough to fall to the ground.
The ice crystals that make up snowflakes are symmetrical (or patterned) because they reflect the internal order of the crystal’s water molecules as they arrange themselves in predetermined spaces (known as “crystallization”) to form a six-sided snowflake.
Ultimately, it is the temperature at which a crystal forms — and to a lesser extent the humidity of the air — that determines the basic shape of the ice crystal.
Thus, we see long needle-like crystals at -5C (23 degrees F) and very flat plate-like crystals at -15C (5 degrees F)
The intricate shape of a single arm of the snowflake is determined by the atmospheric conditions experienced by entire ice crystal as it falls.
A crystal might begin to grow arms in one manner, and then minutes or even seconds later, slight changes in the surrounding temperature or humidity causes the crystal to grow in another way.
Although the six-sided shape is always maintained, the ice crystal (and its six arms) may branch off in new directions.
Snowflakes are agglomerates of many snow crystals.
Most snowflakes are less than one-half inch across (1.3cm)
Under certain conditions, usually requiring near-freezing temperatures, light winds, and unstable, convective atmospheric conditions, much larger and irregular flakes close to two inches (5cm) across in the longest dimension can form.
So snow can fall when surface temperatures are above freezing as long as atmospheric temperatures are below freezing and the air contains a minimum moisture level (the exact level varies according to temperature).
In general snow that falls at temperatures close to 0C or snow with strong winds do contain about 1 inch (2.5cm) of water per ten inches (25 cm) of snowfall.
However ten inches of fresh snow can contain as little as 0.10 inches (ie a tenth less than the average) of water and as much as 4 inches of water (ie 4 times as much as the average), depending on crystal structure, wind speed, temperature, and other factors.
Icicles form as the result of cycles of melting and freezing.
Typically this cycle will occur more often on the south sides of buildings, melting in the day and freezing at night, whereas on the north sides, without the benefit of the warmth of the sun, melting does not occur as often.
Although it depends on each snowflake’s size and mass and the surrounding environmental conditions, most flakes fall at speeds of 1 to 4 mph
The largest, heaviest snowflakes can reach speeds up to 9 mph, but the typical flake descends toward the ground at about 1.5 mph and takes around an hour to reach the ground, according to the Met Office