Most of the various classifications that the meteorologist uses to describe snowfall has to do with the rate at which the snow falls. To the layman, these terms can be confusing, and oftentimes in the media they are incorrectly used. This article is intended to provide a guide to the various weather terms used to describe snow.
What is a Snow Flurry?
Snow flurries are the lightest form of snow precipitation. Another way to think of it would be the wintertime equivalent of drizzle, but in frozen form. Snow flurries are often brief in duration, and very light. Rarely will snow flurries cause any type of accumulation.
It is also sometimes referred to as a light snow shower, and is classified as snow that meets the visibility requirements for light intensity snowfall.
Various Snowfall Rate Classifications
The National Weather Service (U.S.) splits heavier and steadier snow events into three separate classifications: light, moderate, and heavy. To discern between these various levels of intensities, the NWS uses measurements of visibility.
When falling snow reduces visibility above 5/8 mile, it is considered "light snow." While there is no upward visibility level to differentiate light snow and snow flurries, the volume of snowflakes in the air are a good indication of the difference.
Below 5/8 mile and down to 1/4 mile, the snowfall rate is classified as "moderate snow." Typically, when reported, moderate snow is reported without any kind of modifier (i.e. "Snow"). When visibilities drop to 1/4 or less, it is referred to as "heavy snow."
There is no general relationship between snowfall intensity and rates of accumulation, as other factors including air and ground temperature must also be factored in.
What is a Snow Shower?
Like rain showers in the spring, snow showers are brief periods of moderate precipitation, in this case snow. One of the most noticeable properties of the snow shower is its sudden onset, and sudden ending. Visibilities as with moderate snowfall will fall below 5/8 mile for a period time, and the rate of precipitation will likely be variable.
In some cases, snow showers can bring a quick accumulation of an inch or two depending on their intensity and duration.
What is a Snow Squall?
The "big brother" of the snow shower, a snow squall is essentially a heavy snow shower, that like the squall lines of the summer is characterized by its heavy precipitation rates and often gusty winds. These are most typically found along strong winter time cold fronts, and as part of lake effect snow off of the lee-facing side of lakes. In some cases, these events can produce several inches of snow in under an hour
Due to the combination of the heavy precipitation and winds, snow squalls can be especially dangerous to drivers. Visibilities may drop rapidly, and snow may make roads slick rapidly. Use caution when venturing out in snow squall conditions.
Other Snow-related Terms
Beside the terms listed above, there are some other terms that are commonly used during the winter. Here are just a few of them, courtesy of the NWS' weather glossary:
Blizzard: Severe winter storms with gusty winds, blowing snow, and heavy falling snow that lasts for an extended period of time. For more on this winter event, see this article.
Blowing and drifting snow: Already fallen snow that is picked up and blown about by the wind. In some cases, this can severely limit visibilities and cause disorientation for those caught in it. For it to be called blowing snow, it must be picked up to a height of eight feet. Below this it will be called "drifting snow."
Whiteout: Blowing, drifting, or falling snow that causes visibility to fall to near zero for an extended period of time.
Sources: Various Authors,AMS Glossary of Meteorology, Second Edition. Published in 2000 by the American Meteorological Society, electronic version referenced.
