Weather map symbols for clouds

Temperature and moisture

After air begins to cool and then becomes saturated, sublimation or condensation starts the cloud-forming process. The air within the newly formed cloud layer is either stable or unstable. This stability or instability will determine the type of cloud structure. This is because stable air resists convection while unstable air prefers convection. Cloud formation in stable air develops horizontally in uniform, sheet-like layers called "strata". When an unstable layer of air is forced upward by convection, a cloud forms vertically. How high into the atmosphere the cloud shapes itself depends upon the depth of the unstable layer. These clouds tend to pile up in a heap or "cumulus." They are characterized by their lumpy, billowy shapes. Vertical heights of cumulus clouds vary from the shallow fair weather cumulus to the giant thunderstorm cumulonimbus clouds. The convection process occurring in unstable air will give a bumpy ride to an airplane passing through it. In stable air flying is usually smooth.

All in all clouds give pilots and others who monitor the weather an indication of air motion, stability and moisture. For basic identification purposes, clouds are divided into four families: high clouds, middle clouds, low clouds and vertically advanced clouds.



Unmanned Aerial Vehicle

An Altair unmanned aerial vehicle (UAV) is pioneering climate and environmental research for NASA and the National Oceanic and Atmospheric Administration (NOAA).

The Altair has been used to develop methods of predicting extended days of rain in time to mitigate natural disasters like floods and mudslides. Its sophisticated sensor suite includes a passive microwave radiometer that will be used to measure atmospheric rivers—air currents laden with moisture that sweep up from the tropics. These atmospheric rivers, flowing along polar cold front boundaries, can cause major floods on the U.S. west coast. In addition, the Altair UAV has been fitted with a pod-mounted infrared imaging sensor to map wildfires in central and southern California.

The Altair UAV Altair was developed to conduct high altitude scientific research and to perform flight operations in national air space. With a wingspan of 86 feet, it is designed for operations above 15,000 meters (50,000 feet).

The Altair is a modified version of the General Atomics Aeronautical Systems, Inc. MQ-9 Predator B unmanned aerial vehicle (UAV) that was developed for the U.S. Air Force. Differences from the military aircraft include a longer wingspan to enable the Altair to sustain higher altitudes, a triplex redundant flight control system and modified avionics and electronics to support its civil missions. It is flown by a pilot from a ground control station, with flight commands and data relayed to and from the aircraft via either a satellite communications link or by direct radio link. The Altair also has full Global Positioning System (GPS) capability to assist in navigation.

For basic identification purposes clouds are divided into four families: high clouds, middle clouds, low clouds and vertically advanced clouds.

Low Clouds

Low Clouds

The low cloud family members are cumulus, fractocumulus, stratocumulus, stratus, fog, and fractostratus clouds. These clouds are nearly entirely composed of water, and sometimes the water is supercooled. Low clouds at temperatures below freezing can also hold snow and ice particles. The bases of these clouds are usually found near the surface to about 6,500 feet.

Middle Clouds

Middle Clouds

The middle cloud family members are altocumulus, and altostratus clouds. Lenticular clouds are often typically included this family. Middle clouds are mainly composed of water, most of which is supercooled. The bases of these clouds are usually found around 6,500 to 23,000 feet.

High Clouds

High Clouds

The high cloud (cirriform) family includes cirrus, cirrocumulus, and cirrostratus. They are made up almost entirely of ice crystals. The bases of these clouds are usually found around 16,500 to 45,000 feet.

Vertically Advanced Clouds

Vertically Advanced Clouds

The vertically advanced cloud family members are nimbostratus, towering cumulus and cumulonimbus clouds, featuring two layers of moisture. These clouds usually contain supercooled water above the freezing level. As a cumulus cloud grows to great heights, water in the upper part of the cloud freezes into ice crystals forming a cumulonimbus. The bases of these vertically advanced clouds range from 1,000 feet (or lower) to a towering 10,000 feet or higher.

Cross Section of a Thunderstorm

In general, the following is a list of observations that a pilot can make regarding stable/unstable air and clouds.

See the chart below for a brief description of each cloud type and its effects on flight.

Cloud Types and Flight Effects Chart

Cloud Type

Effects on Flight


no significant icing; turbulence in dense, banded cirrus


may contain highly super-cooled water droplets resulting in some turbulence and icing


little if any icing; no turbulence; restricted visibility


small amounts of icing; some turbulence


moderate amounts of icing; little to no turbulence; restricted sunlight

altocumulus castellanus

unstable air; rough turbulence with some icing

standing lenticular
altocumulus clouds

very strong turbulence


very little turbulence; can pose serious icing problems if temperatures are near or below freezing


little or no turbulence; hazardous icing conditions if temperatures are near or below freezing; when associated with fog or precipitation can create conditions of greatly reduced visibility


some turbulence; possible icing at subfreezing temperatures; ceiling and visibility better than with low stratus clouds


shallow layer of unstable air will give some turbulence, but no significant icing

towering cumulus

very strong turbulence with rain showers; some clear icing above freezing level


unstable air throughout; violent turbulence; strong possibility for icing


GOES SatelliteNASA works with the National Oceanographic and Atmospheric Administration (NOAA) to develop and deploy satellites that have proven to be critical for monitoring and forecasting the weather. These systems include geostationary operational environmental satellites (GOES) for short-range warning and "now-casting", and polar-orbiting satellites for longer-term forecasting. Both types of satellite are necessary for providing a complete global weather monitoring system.

GOES satellites orbit at about 35,800 km (22,300 miles) above the Earth, high enough to allow the satellites a full-disc view of the Earth. Because they stay above a fixed spot on the surface, they provide a constant vigil for the atmospheric "triggers" for severe weather conditions such as tornadoes, flash floods, hailstorms, and hurricanes. When these conditions develop the GOES satellites are able to monitor storm development and track their movements. GOES satellite imagery is also used to estimate rainfall during the thunderstorms and hurricanes for flash flood warnings, as well as estimates of snowfall accumulations and overall extent of snow cover. GOES observations have proven helpful in monitoring dust storms, volcano eruptions, and even the spread of forest fires. Television Weather Satellite

NASA and NOAA are slated to launch a new generation of satellites in 2013. The new program, called the National Polar Orbiting Operational Environmental Satellites System (NPOESS), was created as a cost-saving measure in the 1990s. NPOESS will merge the nation’s civilian weather satellite programs with the Department of Defense’s Defense Meteorological Satellite Program (DMSP). NOAA will remain responsible for operating NPOESS satellites through 2026, and NASA will be responsible for injecting cost-effective new technology into NPOESS satellites.

NASA engineers are preparing to launch a demonstration mission in 2010—the N-POESS Preparatory Project (NPP)—which will test critical sensors slated to fly on the NPOESS satellites.