![]() In addition to snow, you can also have sleet, freezing rain, hail and graupel. Snow isn’t the only form of frozen precipitation, but it is the most complex. When a raindrop falls to the ground surface, two forces, i.e., the gravity and drag forces act on it. Drizzle which drop size is less than 0.5mm falls at the speed of 2 m/s (0.5 mph). A large raindrop of about 5 mm size falls at the rate of 9 m/s (20 miles per hour). What’s interesting about snowflakes is that independently they are quite delicate, but in large enough quantities they can shut down a city. The heavier the drop, the greater will be the falling speed. In order to get such large snowflakes, however, you need very specific weather conditions including near-freezing temperatures, light winds and unstable atmospheric conditions.įrozen precipitation and travel do not mix well The NSIDC explains that while most snowflakes are less than 0.5 inches across, some can reach sizes nearing 2 inches across. It is true, however, that most heavy snowfalls occur when there is relatively warm air near the ground-typically -9 degrees C (15 degrees F) or warmer-since warmer air can hold more water vapor.” 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. “While it can be too warm to snow, it cannot be too cold to snow. “As a general rule, though, snow will not form if the ground temperature is at least 41 degrees F (5 degrees C),” according to the National Snow and Ice Data Center ( NSIDC) website. Precipitation continues to fall as snow when the temperature remains at or below 32 degrees F from the cloud base to the ground. Most precipitation that forms in wintertime clouds starts out as snow because the top layer of the storm is usually cold enough to create snowflakes. You really have to look at the entire column of air to know what type of precipitation you will get. The temperatures at the surface are only part of the story though. “Īlthough the core six-sided shape is always maintained, each of the six arms may branch off in new directions, or change shape as it incurs slight changes in the surrounding temperature or humidity, but because each of those arms is experiencing the exact same atmospheric conditions, all the arms will look identical.Īs the famous quote says “To appreciate the beauty of a snowflake it is necessary to stand out in the cold.” From small particles, you need a microscope to see it turning into falling rain. Thus, we see long needle-like crystals at 23 degrees F and very flat plate-like crystals at 5 degrees F. The actual shape of falling rain is more like a hamburger bun and can be split in half by air resistance at times. “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. Therefore, they all end up unique, while still maintaining the basic six-sided structure. ![]() Each individual snowflake encounters slightly different atmospheric conditions on its path from sky to ground.
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