Weather maps provide information on the atmospheric conditions at a particular time over a large area. The amount of information on a weather map is great.

Let's walk through the different symbols and information that can be found here and learn to interpret them!

Here is one example of a weather map.

Weather maps provide information on fronts.

When air masses collide, they form a front. There are four types of fronts: cold fronts, warm fronts, stationary fronts, and occluded fronts. Each has its own symbol on a weather map, and each represents a different type of weather.

Cold fronts form when a fast-moving cold air mass over takes a warm air mass.

As the fast moving cold air mass travels in, the warm air is pushed upward along the edge of the front. This air expands (word missing? please provide it) and cools, releasing its water vapor. Clouds form.

Cold fronts can produce heavy rain or snow. If the original warm air mass did not have much moisture, then cloudy skies may prevail.

Cold fronts tend to move quickly, which causes abrupt weather changes. Summer thunderstorms are often caused by cold fronts.

Colder, drier air moves in after a cold front. The skies may become clear, the wind may shift, and the temperatures may drop. This is the relief you may feel after a summer thunderstorm.

A cold front is shown on a weather map by the following symbol:

The triangles in this symbol of a cold front point in the direction of the movement of the front. The symbol for a cold front will always be in blue in a colored weather map.

A warm front occurs when a warm air mass overtakes a slower moving cold air mass.

As a warm air mass moves into an area with a slow moving cold air mass, the warm air mass will rise up over the cold air mass. This is because the warm air is less dense. If the warm air is moist, then a light rain or snow may fall at the edge of the front. Warm air masses with little moisture will create clouds. This warm front will move slowly and is at a very low angle with respect to the ground. This creates cloudy conditions in an area for several days.

After a warm front passes, the weather will typically be warm and humid.

Warm fronts are represented by the following symbol on a weather map:

Warm fronts move slowly and give days of scattered showers and clouds.

Stationary fronts form when cold air masses and warm air masses meet.
Sometimes when this happens, neither of the air masses can move.

The moisture from the warm air mass will condense when it comes in contact with the cold air mass. Clouds, fog, rain, or snow are all likely to form in a stationary front.
Stationary fronts often become stalled over an area. This would bring days of steady rain or snow and cloudy conditions.

Stationary fronts are represented by the following symbol on weather maps:

Notice how the symbol for stationary fronts shows a warm front and a cold front meeting.

Occluded fronts are the most complicated fronts of all.

In an occluded front, a warm air mass gets caught between two cold air masses.

Denser, cooler air moves under a warm air mass, pushing it upward. This denser, cooler air may meet and mix. The temperature near the ground becomes cooler as the warm air becomes cut off from the ground. The warm air will eventually turn (?) cold, condensing any water vapor it was carrying. This will in turn create cloudy weather with the chance of snow or rain.

Occluded fronts are represented by the following symbol on a weather map:

Weather maps also show information about the pressure conditions of the atmosphere. Have you ever seen a large H or L on a weather map? These tell much about the conditions in the atmosphere as well.

Some areas on a weather map are marked with a large L. This stands for "low.". It is an area of relatively low atmospheric pressure. The center of a low pressure area is called a cyclone.

Warm air in the center of a cyclone rises. This reduces the air pressure. Air pressure is higher in the areas surrounding the cyclone. This brings in cooler air from those areas. The movement of this cooler air creates winds spiraling in toward the center of the system. In the Northern Hemisphere, these winds spin counterclockwise.

The rising warm air in a cyclone allows clouds to form and precipitation to occur.

Low pressure areas are associated with clouds, precipitation, and windy conditions.

An area of high pressure is shown on weather map with a large H. Areas of high pressure are also called anticlones. The winds typically spiral outward from the center of an anticlone. The air is moving toward areas of lower pressure. This air moves out from the center of the anticlone, and it drags cooler air from the troposphere down with it.

Areas of high pressure are associated with dry, clear weather.

In addition to information about fronts and pressures, weather maps also include information about cloud cover, wind speed, and specific weather events happening at certain times.

The following chart is used to represent cloud cover on a weather map.

Some charts have cloud cover in percents; others are more general like the one here. Either way, the symbols are fairly similar and represent the amount of cloud cover in the sky.

Wind speed and direction is shown with arrows, with small lines or flags coming off the ends.

The symbols for wind speed are given below. Sometimes, wind speed is given in knots. Other times it might be given in miles per hour. Bbe sure to check the units on your weather map.

Tthe symbols point toward the compass direction that the wind is originating.

For example: This symbol represents a northwest wind blowing at 25 knots (assuming that North is toward the top of the screen).

Other, more specific weather events are shown on a weather map with the following symbols.

Weather maps also give information about temperature and pressure.

Isobars are lines that connect places on a weather map of the same pressure. Air pressure readings are usually expressed as either inches of mercury or in millibars.

Isotherms are lines that connect places of equal temperatures. You may find these lines crisscrossing a weather map.

Fun fact: weather prediction is tricky. Forecasts for the following week are based on the forecasts for all the days between now and then. A slight change in one day's weather can affect the whole week. This is called the butterfly effect. In other words, tiny disturbances can cause big changes later on!