Weather front
Air pressure atmospheric front
A weather front is a transition zone between air masses with different temperatures or moisture. Wind, cloud and precipitation often change around it.
A transition, not a wall
On a map, a front is just a line. In the atmosphere, it is a three-dimensional, usually sloping transition zone. The line marks its approximate position at the surface. Rain may start well ahead or become heavier behind it.
The main types of front
On small screens, scroll sideways to see all columns.
| Front | What happens? | What often follows |
|---|---|---|
| Warm front | Warmer air advances and rises over colder air. |
Increasing layered cloud and prolonged precipitation. |
| Cold front | Colder air advances and lifts warmer air. |
A wind shift, cooling, showers or thunderstorms. |
| Occlusion | A cold front catches a warm front and lifts warm air away from the surface. |
Often widespread cloud and precipitation. |
| Stationary front | The boundary moves very little. |
Persistent conditions, sometimes with prolonged rain. |
Typical does not mean guaranteed
Not every cold front produces a thunderstorm, and not every warm front brings steady rain. Moisture, stability and the strength of lifting all matter. Sometimes a front is most noticeable as a change in wind direction.
When will it arrive?
Front charts show the broader picture. Current observations, radar and short-range forecasts are better for local timing. A line on the map is not an appointment scheduled to the minute.