Typical isobaric pattern associated with a prefrontal squall line. trailing cold front. However, if the zone is narrow, the wind shift may not be noticeable on surface charts. There is generally a large drop in temperature because of the cooling of the air by precipitation. After passage of the squall line, the wind backs to southerly before the cold frontal passage. When the squall line dissipates, severe weather may develop along the fast-moving cold front.
Turbulence is severe in the squall-line thunderstorms because of violent updrafts and downdrafts.
Above the freezing level, icing may occur. Hail is another possibility in the squall-line thunderstorm and can do extensive structural damage to an aircraft. Under the squall line, ceil-ing and visibility may be reduced because of heavy rain showers. Fog is a rare occurrence because of the strong wind and gusts, but it may be found in isolated cases. Tornadoes frequently occur with squall lines when the warm air mass is extremely unstable.