Squall Line

A narrow, but long line (up to hundreds of kilometers long) of severe thunderstorms that typically form along or ahead of a cold front. 

Squall lines, like thunderstorms can cause many hazardous impacts including:

• Turbulence – severe turbulence caused by updraft and downdraft regions of a squall line.
• Lightning strikes – lightning strikes can strike an aircraft either on the ground or in flight.
• Icing – water droplets present in a squall line may freeze on an aircraft producing icing conditions. 
• Reduced visibility – heavy rain that accompanies squall lines can cause reduced visibility. 
• Wind – both wind shear and microbursts can cause rapidly changing wind speeds, especially in the lower levels of the atmosphere and right ahead of the squall line.
• Tornadoes – although most squall lines do not produce tornadoes, it is possible.
• Hail – squall lines that produce hail can damage aircraft.
• Flash flooding – heavy downpours in a short period of time can cause flash flooding on the ground.