Types of fronts on a weather map: Be your own weatherman

Cold, warm, stationary, occluded, and drylines: here's an easy to follow guide

Written by Ed Oswald

Published:

types of fronts weather map header image

Ever wonder what the types of fronts you see on the weather map mean? As part of our continuing weather education series, we thought an explainer would be helpful. So let’s get started.

The polar and subtropical jets separate air masses. This boundary is known as a front. If it sounds a bit militaristic, it is because meteorologists gave these boundaries this name for the similarity to a military unit moving across the battlefield.

Although not a hard and fast rule, most of these fronts will ride along ripples on the polar and subtropical jets, changing the weather as they pass. Four types of fronts exist: cold, warm, occluded, and stationary.

types of fronts
The four types of fronts most commonly seen on a weather map.

Infographic

We’ve distilled the information below down to an easy-to-understand infographic for our subscribers. For performance reasons, a lower-quality image is shown on this page. To save the full-size image to your computer, click the “download” button below the infographic.

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The Three Main Types of Fronts

Some cold fronts may tear through violently with high winds and storms with noticeably cooler air masses behind them. In contrast, others will pass with barely any noticeable difference except a change in humidity and more pleasant weather.

Warm fronts are typically much less benign. Severe storms with tornadic activity can occur near warm fronts, thanks to increased amounts of spin. Occluded fronts are mixtures, any combination of weather, temperature, and/or humidity change. Their effects are widely variable.

Stationary fronts, when a boundary stays in place, sit over the same area for days at a time and frequently are the cause of excessive rainfall in the summer months and “stagnant” weather patterns.

Cold fronts on a weather map are typically depicted as a blue line with triangles on it, the triangles indicating the direction of movement. Warm fronts are red lines with half-circles, those half-circles pointing in the direction of movement, while occluded fronts are shown in purple with alternating triangles and half-circles.

Cold Fronts

The cold front is typically the most active. There is a noticeable wind shift and increase in wind speed as it passes, and both the temperature and humidity drop – sometimes quite significantly. It typically moves west to east over the US, replacing warmer, more humid air masses. Because colder air is denser than warmer air, a cold front ‘scours’ warm air out, as shown below in the diagram.

types of fronts - cold front diagram
Cross-section of a cold front.

What weather does a cold front bring?

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Before PassingWhile PassingAfter Passing
Windssouth-southwestgusty; shiftingwest-northwest
Temperaturewarmsudden dropsteadily dropping
Pressurefalling steadilyminimum, then a sharp riserising steadily
Cloudsincreasing: Ci, Cs and CbCbCu
Precipitationshort period of showersheavy rains, sometimes with hail, thunder, and lightningshowers then clearing
Visibilityfair to poor in hazepoor, followed by improvinggood, except in showers
Dew Pointhigh; remains steadysharp droplowering

Note: Ci = cirrus, Cs = cirrostratus, Cb = cumulonimbus, Cu = cumulus, As = altostratus, Ns = nimbostratus, St = stratus,  Sc = stratocumulus, Tcu = towering cumulus

Warm Fronts

Warm fronts do the opposite of cold fronts, so warmer air replaces colder air. Warmer air is less dense, so it will move over the top of colder air as it travels (the opposite of a cold front — see diagram). Warm fronts typically move from south to north in the Northern Hemisphere, with increased air temperature and humidity behind them. In some cases, severe weather may break out just behind a warm front due to increased instability.

types of fronts warm front diagram
Cross-section of a warm front.

What weather does a warm front bring?

Before PassingWhile PassingAfter Passing
Windssouth-southeastvariablesouth-southwest
Temperaturecool-cold, slow warmingsteady risewarmer, then steady
Pressureusually fallingleveling offslight rise, followed by fall
Cloudsin this order: Ci, Cs, As, Ns, St, and fog; occasionally Cb in summerstratus-typeclearing with scattered Sc; occasionally Cb in summer
Precipitationlight-to-moderate rain, snow, sleet, or drizzledrizzle or noneusually none, sometimes light rain or showers
Visibilitypoorpoor, but improvingfair in haze
Dew Pointsteady risesteadyrise, then steady

Note: Ci = cirrus, Cs = cirrostratus, Cb = cumulonimbus, Cu = cumulus, As = altostratus, Ns = nimbostratus, St = stratus,  Sc = stratocumulus, Tcu = towering cumulus

Occluded Fronts

Occlusion is where a cold front catches up to a warm front. As a result, the air out ahead of an occlusion will be different in some way from the air behind it. Generally speaking, in a warm occlusion, the air behind an occluded front is even warmer than the air ahead of a warm front. In a cold occlusion, the most common, the air behind the occlusion is colder than the air out ahead of the warm front (not colder than the air ahead of a cold front). See the chart below.

types of fronts occluded front
Cross-section of an occluded front.

What weather does an occluded front bring?

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Before PassingWhile PassingAfter Passing
Windssoutheast-southvariablewest to northwest
Temperature
Cold Type 
Warm Type

cold-cool 
cold

dropping 
rising

colder 
milder
Pressureusually fallinglow pointusually rising
Cloudsin order: Ci, Cs, As, NsNs, sometimes Tcu and CbNs, As or scattered Cu
Precipitationlight, moderate or heavy precipitationlight, moderate or heavy continuous precipitation or showerslight-to-moderate precipitation followed by general clearing
Visibilitypoor in precipitationpoor in precipitationimproving
Dew Pointsteadyusually a slight drop, especially if cold-occludedslight drop, although may rise a bit if warm-occluded

Note: Ci = cirrus, Cs = cirrostratus, Cb = cumulonimbus, Cu = cumulus, As = altostratus, Ns = nimbostratus, St = stratus,  Sc = stratocumulus, Tcu = towering cumulus

Stationary Fronts

As the name implies, a stationary front is a cold or warm front that is no longer moving. The blue triangles of the cold front point toward the warmer air, and the red half-circles of the warm front towards the cold. One of its most noticeable features is a marked temperature and wind direction difference on each side. A stationary front can also be a focal point for atmospheric lift and convergence, creating clouds and precipitation. These fronts are a common cause of excessive precipitation year-round.

Drylines

Most areas of the country don’t experience these often, but since this is a book on American weather it’s important to mention the dryline. These fronts are most commonly found in the Plains during the summer. You can think of these drylines as a difference in humidity: warm, humid air on one side and dry, hot air on the other. This is typically shown as a dashed yellow or orange line on a weather map. In the summer months, drylines trigger thunderstorms, often severe.

Want to learn more?

This post is an excerpt from my book, Weather Watch: An Introduction to America’s Weather and Climate, available on Amazon, and free for Kindle Unlimited subscribers!

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Ed Oswald

Ed Oswald has nearly two decades of experience in technology and science journalism, and specializes in weather stations and smart home technology. He's written for Digital Trends, PC World, and TechHive. His work has also appeared in the New York Times. When he isn't writing about gadgets, he enjoys chasing severe weather and winter storms.