Changeable westerly winds
In a westerly wind situation, the passage of a frontal system with warm and cold fronts leads to changeable weather. At first clouds will gather before precipitation sets in with the passage of the warm front. In winter, this can lead to heavy snowfall on the Swiss Plateau. Later, when the warm sector (the zone between the warm front and the cold front) passes through, the clouds will gradually dissipate as they get further away from the low-pressure centre.
A cold front also announces itself with clouds, but the cloud band is significantly narrower than that of a warm front. In summer, thunderclouds usually form on a cold front; in winter, this is the exception rather than the rule. On the back side of a cold front, thunderclouds will form in the cold polar air, especially during the day, and a marked cooling may occur.