What is a squall?

The squall is a weather term that does not get used often enough… unfortunately… because not many people are familiar with it.

From the Glossary of Meteorology:

1. A strong wind characterized by a sudden onset, a duration of the order of minutes, and then a rather sudden decrease in speed. In U.S. observational practice, a squall is reported only if a wind speed of 16 knots or higher is sustained for at least two minutes (thereby distinguishing it from a gust).

2. In nautical use, a severe local storm considered as a whole, that is, winds and cloud mass and (if any) precipitation, thunder and lightning.

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Think of it as a gusty rain or snow storm… but one that last only 5-15 minutes. Snow squalls are common in Virginia’s Western Highlands and New River Valley, especially in those counties along the West Virginia line.

Occasionally, a snow squall will sneak east of the Blue Ridge and into central or southern Virginia. The sky will turn dark and the snow will come down at a heavy clip for 5-15 minutes. The wind will increase to a level between 20-30 miles per hour, and it would seem that a blizzard were about to take place.

But just as quickly as it settles in, it stops. The wind speed decreases and breaks of sunshine return.

During the spring and summer, we have occasional rain squalls. Usually they are accompanied by thunder and lightning, so we call them thunderstorms. In the fall, the heavy rain and gusty winds are still common, but there is typically not enough energy in the storms to develop lightning.

(More energy in the storm causes the storm to grow higher into the atmosphere, forming more ice crystals, which in turn separates electrical charges inside the cloud, resulting in lightning.)

Typically, squalls form in an unstable atmospheric environment. That means that the temperatures aloft (typically between about 2000-5000 feet) are very low. Air rapidly rises into that cold air like a hot air balloon, where its moisture condenses, forms clouds, and precipitates back to the ground. The process takes place quickly, so there is not enough time for squalls to organize into a large-scale snow storm that lasts for a few hours.

The most glaring exceptions are the lake effect squalls. Sometimes, the individual squalls coming off of a lake are narrow in space, but very long. If the steering winds are parallel to the squalls, then the same location can get snow for several hours. This is common in areas immediately east of the Great Lakes, and it is responsible for tremendous differences in snowfall over just a few miles.


About seansublette

Meteorologist at Climate Central. Broadcast meteorologist in Virginia from 1995 to 2015. Born and raised in Richmond, VA. Penn State alumnus. Loves baseball and the rock band Rush. Views are independent of my employer. Past performance does not guarantee future results.
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