Clouds tell you about stability, turbulence and icing. These are the groups the FAA expects a remote pilot to recognize.
Know the four groups. High clouds (cirrus, cirrostratus, cirrocumulus) form above 20,000 feet AGL and pose no real turbulence or icing threat. Middle clouds (altostratus, altocumulus) can bring turbulence and icing. Low clouds include stratus. Towering cumulus and cumulonimbus mean instability, and cumulonimbus is the most dangerous.
High clouds are ice crystals and usually form only in stable air. Middle clouds form around 6,500 feet AGL and extend up to 20,000 feet AGL: altostratus can produce turbulence and may contain moderate icing, and altocumulus may contain light turbulence and icing. The word nimbus comes from the Latin for rain, so nimbus clouds bring steady precipitation.
Clouds with extensive vertical development build from the low to middle cloud-base region up into high altitudes. Towering cumulus indicates instability and turbulent air, and often develops into cumulonimbus. Cumulonimbus clouds contain large amounts of moisture and unstable air and usually produce hazardous weather such as lightning, hail, tornadoes, gusty winds and wind shear.
Standing lenticular altocumulus clouds form on the crests of waves created by barriers in the wind flow, and they are a good indication of very strong turbulence. How clouds limit a Part 107 flight is explained on our Part 107 visibility and cloud clearance page.
Sources: FAA-H-8083-25C (PHAK), p. 300 · Remote Pilot Study Guide, p. 33 · FAA-H-8083-28B, p. 152 · FAA-H-8083-25C (PHAK), p. 302
FAA-H-8083-25C (PHAK), p. 300
High clouds form above 20,000 feet AGL and usually form only in stable air. They are made up of ice crystals and pose no real threat of turbulence or aircraft icing.
FAA-H-8083-25C (PHAK), p. 300
Towering cumulus clouds indicate areas of instability in the atmosphere, and the air around and inside them is turbulent.
Remote Pilot Study Guide, p. 33
To pilots, the cumulonimbus cloud is perhaps the most dangerous cloud type. It appears individually or in groups and is known as either an air mass or orographic thunderstorm.
Remote Pilot Study Guide, p. 33
Standing lenticular altocumulus clouds are formed on the crests of waves created by barriers in the wind flow. The clouds show little movement, hence the name standing.
Sources: FAA-H-8083-25C (PHAK), p. 300 · FAA-H-8083-25C (PHAK), p. 300 · Remote Pilot Study Guide, p. 33 · Remote Pilot Study Guide, p. 33
Similar to the FAA test, not the actual test questions. Each answer shows its FAA source.
Question 1 of 3
Either Cumulonimbus or towering cumulus will be indicative of turbulence due to their extensive vertical development (and therefore updraft).
FAA source: FAA-H-8083-25C ch. 12, Clouds
Question 2 of 3
This is a rote memory item. Nimbus means rain.
FAA source: FAA-H-8083-28B ch. 12, Cloud classification
Question 3 of 3
Cumulonimbus are always the worst clouds to get near or into.
FAA source: FAA-G-8082-22 ch. 3b, Thunderstorms
Rising air currents make it extremely turbulent, with updrafts and downdrafts that can exceed 3,000 feet per minute. It can also produce large hail, damaging lightning, tornadoes and large amounts of water.
Source: Remote Pilot Study Guide, p. 33
It quizzes you on questions like these, explains why each answer is right with the FAA page behind it, and retests the ones you miss. Free to start: 300 credits every month.
More on this topic: Part 107 weather, task by task.