Resource: Extension cloud guide can help you predict the weather

A key mission of Cooperative Extension is to make science useful in everyday life. Our Extension faculty put together this guide to help people identify clouds and recognize some hints they offer about the weather.

Clouds can do much more than just paint familiar colors across the morning and evening sky – they’re also dynamic atmospheric storytellers that can hint at coming changes in the weather.

In a recent publication from University of Arizona Cooperative Extension, authors Andrew Brischke, Michael Crimmins and Ashley L. Hall outline how observing cloud shapes, altitudes and seasonal shifts allows residents to forecast local weather and understand the invisible mechanics operating in the atmosphere.

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“Clouds can tell us a lot about what kinds of conditions are present at the different levels of the atmosphere,” said Crimmins, an Extension climate science specialist and U of A professor. “They can tell us about the amount of moisture, the speed of the wind and instability that can lead to thunderstorms and heavy rain. The different shapes indicate different aspects of these variables.”

The guide explains that cloud formation requires three ingredients: water vapor, cooling air and microscopic particles known as cloud condensation nuclei.

Originating from dust, fire smoke or salt from ocean spray, these particles provide surfaces where water collects in the same way dew condenses on grass or your car or the outside of a cold glass of water.

Because the atmosphere remains in constant horizontal and vertical motion, condensation and evaporation happen simultaneously, causing these droplets to continually form, dissipate, grow and reshape across the sky as clouds.
To categorize these ephemeral sky formations, meteorologists rely on a system pioneered in 1803 by Luke Howard, recognized as the father of meteorology. Howard's framework categorizes clouds into four core types:

• Cirrus – Wispy, high-altitude clouds (15,000-45,000 feet) formed when warm, low-moisture air rises. 
• Cumulus – These white, puffy clouds look like giant cotton balls. They form between 1,000-6,500 feet and can be precursors to rain.
• Stratus – These featureless clouds often appear as a grey or white overcast or misty fog. They range from the ground to about 1,500 feet elevation.
• Nimbus – Most rain comes from these, which are the densest clouds. Nimbus is often used as a modifier for other cloud types to form genera such as cumulonimbus or nimbostratus.

These four types combine to create ten basic cloud genera ranging from high-altitude cirrocumulus cloudlets to dark, thick nimbostratus rain sheets and multi-level cumulonimbus thunderstorm towers. These ten genera break down into specific species, varieties and accessory clouds based on visual structure, transparency and internal atmospheric processes.

High-level cirrostratus clouds form veil-like curtains of ice crystals that refract sunlight into brilliant halo rings, while mid-level altocumulus castellanus turrets signal high atmospheric instability and afternoon thunderstorm development. Other unique cloud features such as virga — rain that evaporates before reaching the ground — or specialized pyrocumulonimbus clouds generated by intense wildfire convection.

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Knowing these cloud types can tell us what to expect from the weather in coming hours, days or seasonally.

In Arizona, cloud patterns interact closely with topography and seasonal moisture shifts. Winter cold fronts pushing in from the Pacific Ocean bring low-level stratus and mid-level altostratus clouds that produce widespread rain and mountain snow. Spring brings the year's clearest skies under high-pressure ridges, though thin shields of cirrus originating from tropical Pacific convection frequently stream overhead.

By summer, surging monsoon moisture drives intense convective instability, spawning daily towering cumulus and cumulonimbus storms over mountain peaks that often spread into lower desert valleys. Fall brings a return to calmer cirrus and stratocumulus formations as atmospheric moisture wanes. This fall and winter we are likely see impact from a very strong El Niño, which over the summer warmed the surface of the Pacific Ocean to historic levels.

“I expect we will see more high clouds streaming in off the warm Pacific waters ahead of warm and wet storms. As the storms approach the clouds will thicken, lower and hopefully produce widespread rain. El Niño increases the chance of these types of Pacific storms rolling into the southwest frequently through the upcoming winter season,” Crimmins said.

By learning to read these structural indicators and seasonal shifts, desert residents can transform everyday sky-gazing into a practical tool for active weather observation and environmental literacy. Understanding cloud dynamics offers a direct window into the ever-changing weather patterns across the Southwestern landscape.

To learn more about clouds, read this Cooperative Extension publication.