How a Squall Line is Formed

In the business of weather a squall could be nothing more than a sharp burst of wind accompanied by a few other meteorological elements, like rain, thunderstorms or some snow. These short-lived conditions are usually identified by the condition of precipitation such as a “snow squall”, but the unique breed of a squall line is a much more temperamental animal to tame.

The word squall itself was not inducted into weather terminology until the late 19th century, prior it was only an obscure Nordic word Skvala, which was used to describe a yelp or a squeal. The obscurity of the word originated from Norse mythology, but has barely any real concrete origin.

The definition being a squeal is definitely not the appropriate term to use in a storm like a squall line, because between thunderclaps, lightening, and extremely strong winds, this little word can mean a whole lot of trouble.

What Produces a Squall Line?

The first stage of a squall line is the thunderstorm cell, which is formed in a series of developing stages. A cumulus cloud typically begins forming into a thunderstorm cell, when it becomes pushed upward by a column of rising warm air called an updraft. As this column feeds into the cloud it may start to cause some occasional lightening. Once the updraft has fed the storm enough, all the while building up a large accumulation of precipitation though convective processes, the storm begins to fall creating a column of air pushing down. The cool air spreads below the mature cell, and forms a strong gust front (cold air pushing forward), which can likely produce strong winds, heavy rain and even hail.

Now, if you take this thunderstorm cell and connect it to a series of updrafts feeding into a large multi cell system, you form a line of turbulent and unstable thunderstorm cells called a squall line. Most squall lines consist of a long line of storms that are fed by a continuous and developed gust front at the very edge of the storm line. The line of storms can have gaps or breaks, but most squall lines are quite solid. Once a squall line has matured, it can produce large hailstones, extremely heavy precipitation, funnel cloud formations, and even a tornado. One typical characteristic of a squall line is known as the bow echo”, which is an extremely strong down-burst than can force part of the squall ahead of the of line, which monitoring becomes difficult to segregate it from the other main storm line. This bow echo can also quickly develop into a more severe counterpart, possibly becoming its own super cell.

Squall lines are usually layered with independent linear layers that could contain a large volume of precipitation, each layer is pushed by the updraft that feeds the storm line, but is in a constant flux as the downdraft expels the energy built up inside. Squall lines can be typically influenced by subtropical air, in combination to the band of convective layers, but not all storms follow this simple formulation. Squall lines have the capability to cause moderate to major damage, with strong gusting winds, large golf-ball like hail, and the possibility for tornadic activity.

Most squall lines are long and cover hundreds of miles, although certain parts may bow out more than others depending air current, and how strong the gust front can be. Most squall lines are common on flat land; such as the legendary Tornado Alley, Saskatchewan, and Manitoba also see a fair share of these turbulent storm systems. They may appear at first like just another thunderstorm, but look for the dark green hue, or the bulky anvil that protrudes from the leading edge, these are common traits adherent to a squall line.

This storm line may just be a couple of minutes or an hour or so, but don’t wait the last minute to get safely indoors. Lightening and hail are key factors in storm related injuries, and a squall line is a storm that is best weathered, from the safe confines of your warm and cozy home!