Cold front

Let’s look at the various types of fronts.
A cold front occurs when a cold air mass replaces a warm air mass. Because
the cold air is denser and heavier than warmer air, the wedge of cold air pushes under the warm air, lifting it up.
The warm air can be in a stable or unstable condition. Within a stable air mass, there is static stability in the lower layers, very little convection and a low degree of turbulence. In an unstable air mass, static instability prevails, along with greater convection and high turbulence.
If the warm air is stable, it can be overcast with rain occuring ahead of the front.
If the air is unstable, cloud will form, typically cumulus and cumulonimbus accompanied by thunderstorms. Occasionally a continuous line of thunderstorms will form along the front, which is also called a squall line. Squalls may create fierce and destructive conditions such as strong winds, tornados, hail or sleet.
Note: A cold front usually moves faster than a warm front. If it is associated with bad weather, you may have little time for safety preparations and course changes.