A side view of a warm front (A) and how it is represented on a weather map (B)
Click on image for full size
Windows to the Universe image by Lisa Gardiner

Warm Fronts

A warm front is where warm air is pushing into colder air. Warm fronts move more slowly than cold fronts. It is harder for the warm air to move against the cold, dense air.

When a warm front passes through, you will often see high clouds like cirrus, cirrostratus, and middle clouds like altostratus before the front passes. These clouds form in the warm air that is high above the cool air. The clouds become lower and rain is likely at the front. There can be thunderstorms around the warm front sometimes too.

On weather maps, a warm front is shown with a solid red line with red, filled-in half circles along it, like in the map on the left (B). The half circles are on the side of the line where the front is moving. Notice on the map that temperatures are cooler in front of the front than behind it.

Last modified August 12, 2009 by Lisa Gardiner.

You might also be interested in:

Cool It! Game

Check out our online store - minerals, fossils, books, activities, jewelry, and household items!...more

Cirrus

Cirrus clouds are the most common of the High Cloud group. They are made of ice crystals and have long, thin, wispy streamers. Cirrus clouds are usually white and predict fair weather. ...more

Cirrostratus

Cirrostratus clouds belong to the High Cloud group. They are sheetlike thin clouds that usually cover the entire sky. The sun or moon can shine through cirrostratus clouds. When looking at the sun through...more

Altostratus

Altostratus clouds belong to the Middle Cloud group. An altostratus cloud usually covers the whole sky. The cloud looks gray or blue-gray. The sun or moon may shine through an altostratus cloud, but will...more

Rain

Raindrops form when tiny water droplets collide together in clouds to form bigger ones. When they get too heavy, rain falls out of the clouds. Rain is more than 5mm in diameter. The types of clouds that...more

Thunderstorms

Thunderstorms are one of the most exciting and dangerous types of weather. Over 40,000 thunderstorms happen around the world each day. Thunderstorms form when very warm, moist air rises into cold air....more

Weather Fronts

Weather fronts can cause clouds, rain, thunderstorms, gusty winds, and even tornadoes. Usually the skies clear once the front has passed. Weather fronts happen because not all air is the same. In some...more

Cloud Formation and Weather Fronts

Weather fronts can cause clouds to form. Fronts happen when two large masses of air collide into each other at the Earth's surface. Warm fronts produce clouds when warm air replaces cold air by sliding...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part is sponsored in part through grants from federal agencies (NASA and NOAA), and partnerships with affiliated organizations, including the American Geophysical Union, the Howard Hughes Medical Institute, the Earth System Information Partnership, the American Meteorological Society, the National Center for Science Education, and TERC. The American Geophysical Union and the American Geosciences Institute are Windows to the Universe Founding Partners. NESTA welcomes new Institutional Affiliates in support of our ongoing programs, as well as collaborations on new projects. Contact NESTA for more information. NASA ESIP NCSE HHMI AGU AGI AMS NOAA