A cold weather front is defined as the changeover region where a cold air mass is replacing a warmer air mass. Cold weather fronts usually move from northwest to southeast. The air behind a cold front is colder and drier than the air in front. When a cold front passes through, temperatures can drop more than 15 degrees within an hour.
On a weather forecast map, a cold front is represented by a solid line with blue triangles along the front pointing towards the warmer air and in the direction of movement.
There is usually an obvious temperature change from one side of a cold front to the other. It has been known that temperatures east of a cold front could be approximately 55 degrees Fahrenheit while a short distance behind the cold front, the temperature can go down to 38 degrees. An abrupt temperature change over a short distance is a good indicator that a front is located somewhere in between.
A warm weather front is defined as the changeover region where a warm air mass is replacing a cold air mass. Warm fronts usually move from southwest to northeast and the air behind a warm front is warmer and moister than the air ahead of it. When a warm front passes, the air becomes noticeably warmer and more humid than it was before.
On a weather forecast map, a warm front is represented by a solid line with red semicircles pointing towards the colder air and in the direction of movement.
Again, there is typically a noticeable temperature change from one side of the warm front to the other, much the same as a cold front.
If colder air is replacing warmer air, it is a cold front, if warmer air is replacing cold air, then it is a warm front.