Squalls are weather events when the wind suddenly becomes more powerful and violent, often accompanied by stormy weather -- a thunderstorm, abrupt burst of rain, or sudden, heavy, brief fall of snow. The word itself refers strictly only to the sudden increase in wind -- a minimum increase of 18 miles per hour, and a minimum total speed of 25 miles per hour.
In some areas of the world, squalls can occur in fair weather due to local topography -- winds forcing their way through a narrow mountain cleft if they blow from the correct direction, for example. However, many, if not most, occurrences of squalls involve some additional bad weather as well. These squalls are often identified by the type of weather that accompanies them -- rain squalls, thundersqualls, snow squalls, etc.
Different kinds of squalls
Among the many kinds of squalls that occur over various places on the Earth, some are the result of unique local conditions and do not occur elsewhere, while others emerge from normal weather processes.
- A white squall is a windstorm at sea or on the Great Lakes of North America which is not accompanied by clouds or precipitation. White squalls feature intense, sharp increases in the wind for a brief amount of time, and are said to produce huge waves capable of sinking small boats and ships. Some believe the white squall to be a figment of mariner's lore, while others think it is a microburst.
- A snow squall is a sudden, violent snowstorm and wind that occurs on the lee shore of a large lake or ocean in the winter. It is a form of lake-effect snow, when strong winter winds pick up heat and moisture from a wide area of open water, then deposit this moisture as snow on the nearby shores. Snow squalls appear as a white, wall-like cloud projecting over the land, and create a band of narrow but intense snowfall that can make near white-out conditions.
- Squall lines are a fairly thin but extremely violent band of thunderstorms associated with a frontal boundary and sometimes a hurricane. Boisterous, intense winds accompany these storms, and may be intense enough to develop into a derecho. The winds are caused by dense, cold air tumbling to the ground in powerful downdrafts along the stormfront, and may lead to tornadoes.
These sudden gusty winds and the violent weather accompanying them are a hazard everywhere, but are especially dangerous to small boats. They can easily overset such craft and, at the same time, churn up large waves too strong for even an experienced swimmer to resist, resulting in the possible drowning of boaters. Larger ships are usually immune to squall effects, and, indeed, in World War II, naval vessels often used squalls as 'cover' to escape from their enemies when outnumbered.