Fractus clouds are low-altitude, ragged-looking clouds that are also known as scud. They can form in two ways.
Here are some photo examples. In each of theses cases of precipitation-created fractus, the fractus clouds are the irregularly shaped ones that are closest to the ground, under the layer of raining clouds. These scud clouds indicate high humidity (such as due to drizzle falling from higher clouds) and strong winds at low altitude. These clouds are usually isolated and scattered, not overcast (for more information on cloud coverage, see Learning Goal 1c).
When these clouds form over forested hillsides, as in the figures below, the World Meteorological Organization (WMO) calls these stratus silvagenitus. These are due to moisture input to the air from forest canopies, either as the result of evaporation of water from wet leaves after arain shower, or evapotranspiration (exhale) of moisture from inside the leaves.
For more photos of fractus, see Wikipedia - fractus cloud.
Keywords: fractus clouds, lifting condensation level (LCL), precipitation fog, scud
Extra info for experts; Not Needed for this Course.
Use this expert_resources link to find all the items listed below:
- Item - Topic
- World.A.1. - World Meteorological Organization (WMO) "International Cloud Atlas"
- USA.B.1. - Wikipedia list of cloud types
- World.A.2. - WMO: Manual on Cloud Observations (an old, outdated document)
- USA.A.1. - American Meteorological Society (AMS): Glossary of Meteorology
- USA.C.1. - Practical Meteorology (PrMet): Chapter 6, Clouds