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What is a Squall Line?

Have you ever heard the term "squall line" and wondered what exactly it means? Weather jargon can be confusing, but understanding what a squall line is can help you prepare for severe storms and stay safe during inclement weather.

We will explore the definition of a squall line, the conditions that lead to their formation, and the potential hazards they can pose. By learning more about squall lines, you can be better prepared for severe weather events and mitigate any risks that may arise.

What is a Squall Line?

A Squall line is a group of thunderstorms arranged in a long line, which can be hundreds of miles long but are typically only 10 or 20 miles wide. Squall lines often from along or ahead of a front.

Squall lines tend to move quickly and developed into an arched or bowed shape, and are less prone to produce tornadoes than are supercells. They are often accompanied by very high winds, severe turbulence, heavy rain, lightning, icing, and hail.

Squall lines are the type of thunderstorm that is the most dangerous for air traffic. Because the line is usually too tall to fly over, too dangerous to fly through or under, and difficult to circumnavigate. Squall lines are responsible for about 25% of all tornadoes in the United States.

Squall Line Characteristics

Squall Lines are mostly found east of the Rockies in the United States during the spring and summer months, but can be found in other parts of the world. This convection usually moves eastward in the middle latitudes towards the equator into the warm sector.

When squall lines are formed or pass arid regions, dust storms may form due to high winds, lifting dust from the desert floor.  Squall lines require significant low-level warm air and humidity, a nearby frontal zone, and vertical wind shear behind the frontal boundary. The strong winds at the surface is usually dry air intruding into the line of storms, which when saturated, falls quickly to ground also known as microbursts.

Smaller cumulus or stratocumulus, as well as cirrus clouds, can be found ahead of a squall line. Occasionally cirrocumulus or altocumulus clouds may also be present. These clouds are the result of former cumulonimbus clouds having disintegrated, or only minor instability areas ahead of the main squall line.

Squall lines are depicted on weather surface analyses charts as an alternating pattern of two red dots, as shown above.

A few things to remember if you fly into a Squall Line

  • If you are approaching a squall line, the best course of action is to turn around before and land immediately.

  • If you have inadvertently enter a squall line do not turn around, turning around will induce significant load factors that may overstress the aircraft due to the extreme turbulence.

  • Adjust speed as necessary to maintain maneuvering or turbulence penetration speed depending on what is published in the Pilot Operating Handbook (POH).

  • Do not extend the flaps as this will reduce the aircraft’s maximum permitted load factor.

  • Turn on any anti-ice equipment, especially the pitot heat. You will likely experience icing conditions when entering a squall line.

  • Turn the lights in the cockpit up so that they are brighter. The bright light from lightning can cause temporary blindness. Increasing the brightness inside the cockpit will reduce this effect.

Final thoughts

A squall line in aviation refers to a line of severe thunderstorms often associated with strong winds, heavy rain, and turbulence. Pilots must exercise caution when encountering a squall line to ensure the safety of the flight. Understanding the characteristics and potential hazards of squall lines is essential for pilots to make informed decisions and navigate through adverse weather conditions effectively.


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