A squall is a rapid increase in wind speed within a short period of time that may last for only a brief burst of a minute or so before dissipating. Squalls can create hazardous weather conditions and are of special concern for mariners and aviators, who can be in danger if they encounter one without adequate preparation. For the etymologically inclined, this word appears to derive from an Old Norse term meaning “to squeal,” a meaning people can see referenced in another common use of this word, to describe sudden loud cries from a baby.
The causes of these sudden bursts of wind can vary, depending on the region and weather situation, and they tend to be especially common around bodies of water, because air moving over water can change quickly in behavior. Typically, one appears along with a burst of rain, snow, or hail. In lake effect squalls, seen when air moves over a lake and dumps snow or rain on the other side, the wind occurs as warm and cold air meet, leading to an increase in moisture over the lake and sudden precipitation at the other side.
Wind speeds can increase dramatically in a squall, and this may be very dangerous. For sailors, the wind can damage sails or even capsize a boat if it is forceful enough. It may also cause large waves to develop, swamping a watercraft and putting it at risk of sinking. This type of weather is a common and well known hazard on many inland bodies of water, like the Great Lakes in the United States and Canada. High winds can be dangerous for aircraft as well, leading to turbulence and potentially causing pilots to lose control of their planes.
A squall line, a related weather term, is a line of small but highly potent thunderstorms. As these move over the landscape, they will release bursts of high wind and wet weather. Such storm systems are sometimes precursors to a larger storm, including meteorological systems like hurricanes. They have distinctively shaped clouds, making it easy for people to identify them in the distance. Mariners who spot a line of storms may seek shelter to protect their boats in advance of the bad weather.
After the sudden burst of bad temper on the weather's part, the sun may come out. It is not uncommon to see rainbows after such storms, and people may notice phenomena like half a structure being drenched in rain while the other half stays dry and sunny. These small, compact weather systems can pack a punch, and are usually gone very quickly.