What Types of Clouds Cause Summer Rain?

cumulous clouds
Cumulous clouds outside my window.

Summer clouds tell us of the weather to come. Clear blue skies give way to loud booming thunder storms. Here are the clouds you need to know to predict the summer rains.

In the Mid-Atlantic region, July is the rainiest month. This is largely because of hurricane and tropical storms. The summer rain clouds we see are cumulus, cumulonimbus, and mammatus.

Cloud Types

Here is a quick reminder of cloud types.

An artistic depiction of various cloud types. These cloud types include contrails (man made), cumulonimbus, cirrocumulus, cirrostratus, cirrus, altostratus, altocumulus, cumulus, nimbostratus, stratocumulus, stratus, and fog. Source: Christopher M. Klaus. Dept.of Energy. public domain. Accessed 11 June 2021.

Convective Clouds are clouds that are formed by warm air rising into the atmosphere. Warm air is less dense than the surrounding cooler air. Convective clouds are called cumuliform clouds represented by the letters ‘cu’ or the word cumulous.

This makes sense, since in summer the warm air near the ground rises in the atmosphere and forms clouds. We see cumulous clouds in summer. Cumulous clouds are the ones that bring summer rain.

 

cumulus clouds on fine summer days

Fair Weather Clouds

The basic cumulus clouds are called “cumulous humilis”. We know these as fair weather clouds. Cumulus humilis clouds rarely produce rain.

Cumulus clouds are those big fluffy clouds that float across the clear blue sky on a summer’s day. They make everything seem alright. They remind us of sheep or cotton balls or cauliflower. The clouds appear in groups, in lines, or by themselves.

I have watched these clouds pass by in long lines. These long lines are called cloud streets and can be up to 300 miles (480 km) long.

lines of cumulus clouds
cumulus clouds on fine summer days

Cumulus are low-level clouds ranging in altitude of 1,000 to 7,000 feet (200 to 2,000 meters). Cumulous clouds precede other types of clouds like cumulonimbus.

Cumulus clouds occur any time during the year. They are very common inland and over hilly and mountainous terrain. The word cumulus comes from the Latin word, cumulo meaning heap or pile. They are the quintessential summer cloud.

Generally cumulous clouds aren’t rain clouds. But they can bunch up and become rain clouds like cumulonimbus. When cumulus  grow in size they are called towering cumulus or cumulus congestus. They can grow into cumulonimbus or thunderstorm clouds.

 

towering Cumulonimbus cloud
Cumulonimbus cloud Courtesy of The High Fin Sperm Whale,/Wikimedia Commons

Types of Summer Rain Clouds

Cumulonimbus are very tall, towering clouds are the tallest of all the cloud types. These are the “thunder clouds”. They are also called “thunder boomers” and “thunderheads”. They are the final forms for growing cumulus clouds. They form alone or in a line of thunderclouds.

Cumulonnimbus_clouds
Cumulonnimbus_clouds from above. Михал Орела/Wikimedia Commons.

Rising water vapors formed these tall dense clouds. Well developed cumulonimbus have an flat, anvil-shaped top. Cumulonimbus are common from May to September in the Mid-Atlantic region.

Thunderstrom stages
Thunderstrom stages Public domain, via Wikimedia Commons.

These clouds range in height from 2,000 to 39,000 feet (500 to 16,000 meters) or more.

They bring thunders, lightning, heavy rain, and sometimes hail and heavy winds. They can even bring tornadoes, waterspouts, and funnel clouds.

Zachary Hauri, Public domain, via Wikimedia Commons accessed 6/11/2021

Mammatus

Mammatus are spectacular looking clouds, look like bubbles hanging down from the sky. They are be subtly shaped or very defined and amazing. The name of these clouds comes from the Latin word” mamma” meaning “udder” or “breast”.

 

These pouch-like clouds hang down from the base of other clouds, most often from cumulonimbus or thunder clouds. But mammatus can hang from other types of clouds like cirrus, altostratus, or volcanic ash clouds.

Mammatus hanging from cumulonimbus clouds mean a strong thunderstorm. Mammatus are messengers of severe weather ahead.

 

Mammatus and Cumulonmibus clouds
ImUnicke, CC BY 3.0 , via Wikimedia Commons. accessed 6/11/2021

What are the summer rains clouds?

There are other rain clouds, namely the flat low lysing nimbus clouds, which produce a steady rain. These clouds cause rain at any time of the year.

But in winter the air close to the ground isn’t warm and doesn’t rise and produce the towering cumulonimbus of summer thunderstorms.

There is really only one type of cloud that causes those spectacular afternoon thunderstorms, cumulonimbus ones. Big fluffy cumulous clouds gather and bunch up. The warm air close to the ground rises and creates ever taller clouds reaching high into the sky.

The tall clouds become cumulonimbus. And if the storm is severe mammatus clouds hand down from the base of the cumulonimbus.

I think I understand how the summer rain clouds work, but if I need to fine tune my thinking let me know in the comments below.

Cumulonimbus from plane_over_New_York, 30,000 feet
Cumulonimbus from a plane over New York, 30,000 feet by jezFabi/Wikimedia Commons.

Summer Cloud Facts

  • The thicker clouds are, the more sunlight they reflect and the brighter and whiter they appear.
  • Thinner clouds appear darker as the darker blue of the sky is their background.
  • In the Mid-Atlantic region, most summer rain comes from thunderstorms.
  • Relatively low puffy, cumulus clouds are mostly made of liquid water.

More Weather Posts

The Order of a Rainstorm: The Patterns that Predict Rain 

When is Hurricane Season

Nature Journal Prompts: Looking Up

Nature in Summer: An Overview

More Cloud Facts

Convective Clouds https://www.eoas.ubc.ca/courses/atsc113/flying/met_concepts/01-met_concepts/01a-clouds/cumuliform.html – photographs of the various convective or cumulus clouds.

Types of Clouds on the NOAA website

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