Is it ensure, insure, or assure?
|squall line |
A line of sudden, sometimes violent thunderstorms that develop on the leading edge of a cold front. Squall lines can form up to 80 to 240 km (50 to 149 mi) in front of an advancing cold front and can be more than 160 km (99 mi) long. The thunderstorms of a squall line can produce severe weather conditions, such as hail and rain accompanied by winds of over 96 km (60 mi) per hour; they are also associated with tornadoes, especially in spring and early summer.