Because clouds are connected to, and affected by, other weather events, we’ve created the list of weather definitions below (listed alphabetically) to help you expand your knowledge, better understand weather forecasts, and enjoy cloud watching even more.

Crepuscular Ray

A streak of light that seems to radiate from the sun shortly before or after sunset when sunlight shines through a break in the clouds or a notch in the horizon line and illuminates atmospheric haze or dust particles.1

Downslope Flow

A downslope flow is a wind pattern where the winds are flowing from a higher altitude to a lower altitude; this results in thermodynamic warming. This is sometimes referred to as a Chinook wind that occurs downwind of major mountain ranges (and also happens to a lesser extent in the fall over southern California, where Cloud Stock Photos is based out of).

An interesting fact is that air that starts at a certain altitude, rises, and then returns to the original altitude will be warmer than at the start of the process. That’s because rising air cools when saturated at about 6ºC per km (referred to as the moist adiabatic lapse rate) and descending air warms at about 10ºC per km (referred to as the dry adiabatic lapse rate).

El Niño

El Niño is a warming of the eastern Pacific Ocean that causes regional climate shifts, primarily related to precipitation patterns, because it alters the primary storm tracks over the mid-latitudes. For example, southern California is typically wetter during the winter season in El Niño years because the subtropical jet stream is stronger and transports more moisture into the region from the Pacific Ocean.

High Pressure System

A higher pressure weather system is defined by pressure usually above 1020 millibars or 30.13 inches of Hg in the center, has a clockwise circulation in the Northern Hemisphere, and is associated with large-scale descending air motion. Typically, high pressure systems are associated with fair weather conditions including generally clear skies, light winds, and no rainfall.

Low Pressure System

A low pressure weather system is defined by pressure usually below 1000 millibars or 29.53 inches of Hg in the center, and has a counter-clockwise circulation in the Northern Hemisphere (clockwise in the Southern Hemisphere). Low pressure systems are associated with rising air motion and cloud formation, and can be associated with a variety of weather conditions because of the differences in scale. Low pressure areas can be very concentrated — like in a supercell thunderstorm that produces a tornado or a hurricane, and have very vigorous rising air motion — or can be quite a bit larger, as in a winter snowstorm, and associated with a broader area of relatively weak rising air motion.

Marine Layer

A layer of our atmosphere near the surface that is heavily influenced by the ocean. It is typically characterized as having relatively cool temperatures and high moisture content relative to the surrounding land. This layer starts above the ocean and can reach up to 100 km inland if onshore winds are strong enough.


Outflow is a layer of high clouds that streams outward from a weather system that is characterized by rapidly rising air such as in a hurricane or large complex of thunderstorms. 

Subsidence Inversion

A subsidence inversion is a meteorological phenomenon described by a layer of warm air that sits on top of a layer of cold air. Typically, this layer of warmer air is caused by descending air from above and is often linked to high pressure systems at the upper levels of the troposphere.

Typically, as you increase in altitude it gets colder; however, in an inversion this is reversed whereby temperature increases with altitude. That’s an important factor for cloud cover because it changes how air parcels interact with the environment.

Subtropical Jet Stream

A subtropical jet stream is a fast-moving stream of air that forms due to rapid north-south gradients in air temperatures near 30ºN. For example, the subtropical jet is typically stronger over North America in El Nino years as the eastern Pacific is warmer than normal, while farther north there tends to be less variability in ocean temperature leading to a stronger temperature gradient.

Temperature Gradient

A temperature gradient is the horizontal change in temperature over a region; a strong temperature gradient will result in large changes in temperature over short distances in the north/south or east/west directions.

Learn More About Clouds…

Want to learn more about different cloud types? Check out our Cloud Facts page to learn about altostratus, altocumulus, cumulus and cirrus clouds (in plain English, and it’s a quick read!).


  1. "crepuscular ray" 2019. (March 20, 2019).