<P> A cold front is the leading edge of a cooler mass of air , replacing at ground level a warmer mass of air , which lies within a fairly sharp surface trough of low pressure . It forms in the wake of an extratropical cyclone , at the leading edge of its cold air advection pattern , which is also known as the cyclone 's dry conveyor belt circulation . Temperature changes across the boundary can exceed 30 ° C ( 54 ° F ) . When enough moisture is present , rain can occur along the boundary . If there is significant instability along the boundary , a narrow line of thunderstorms can form along the frontal zone . If instability is less , a broad shield of rain can move in behind the front , which increases the temperature difference across the boundary . Cold fronts are stronger in the fall and spring transition seasons and weakest during the summer . When a cold front catches up with the preceding warm front , the portion of the boundary that does so is then known as an occluded front . </P>
<P> A cold front is the leading edge of a cooler mass of air , replacing at ground level a warmer mass of air , which lies within a fairly sharp surface trough of low pressure . It forms in the wake of an extratropical cyclone , at the leading edge of its cold air advection pattern , which is also known as the cyclone 's dry conveyor belt circulation . Temperature changes across the boundary can exceed 30 ° C ( 54 ° F ) . When enough moisture is present , rain can occur along the boundary . If there is significant instability along the boundary , a narrow line of thunderstorms can form along the frontal zone . If instability is less , a broad shield of rain can move in behind the front , which increases the temperature difference across the boundary . Cold fronts are stronger in the fall and spring transition seasons and weakest during the summer . When a cold front catches up with the preceding warm front , the portion of the boundary that does so is then known as an occluded front . </P>
a front where cold air places warm air at the surface
a front where cold air places warm air at the surface
cold front
cold front