How to Read a National Weather Map
You've seen our National Weather Map before, but do you know how to read it?
The red and blue lines on the map are called fronts. A front marks the starting point for a new air mass. When a front passes your location, the temperature changes. The AccuWeather maps show cold fronts (blue), warm fronts (red), and stationary fronts (alternating blue and red.) A cold front marks the leading edge of a change to colder weather. The movement of any front is determined by the movement of the air on the cold side of the front. That's because cold air is more dense than warm air. As cold air plows into a warm air mass, it pushes the warm air up and out of the way. The rapid lift is often sufficient to trigger showers and thunderstorms.
Some people think that when it's very cold outside, it must be a cold front. Actually, that's not true; the cold front is just the boundary line. The coldest air may be hundreds of miles of behind the front. If cold air retreats and allows warm air to advance, we have a warm front. All of the transition from cold to warm occurs on the cold side of the front. This means once the warm front goes by, it is immediately about as warm as it is going to get. As warm air glides over retreating cold air, the lifting results in saturation and often large sheets of clouds with extensive precipitation.
A stationary front is a front that is not moving. The air on the cold side of the front is neither advancing nor retreating. If warm air is trying to advance, it will be forced to rise over the stubborn cold air. This can lead to extensive areas of clouds and precipitation, just as we have with warm fronts.
For more information on how to read our National Weather Map, and for information on many other topics on our site, please click through to our Help Section.
