(Literally, mountain wind.) A hot, dry, squally wind blowing off the interior plateau of South Africa, roughly at right angles to the coast; a type of foehn.

A complex phenomenon in which the surface of the wave folds or rolls over and intersects itself.

In the process it may mix (entrain) air into the water and generate turbulence. The causes of wave breaking are various, for example, through the wave steepening as it approaches a beach, through an interaction with other waves in deep water, or through the input of energy from the wind causing the wave to steepen and become unstable.

A white or milky and opaque granular deposit of ice formed by the rapid freezing of supercooled water drops as they impinge upon an exposed object.

Ice crystals that form in supercooled water that is too turbulent to permit coagulation into sheet ice. This is most common in swiftly flowing streams, but is also found in a turbulent sea (where it is called lolly ice). It may accumulate as anchor ice on submerged objects obstructing the water flow.

A large frost mound of more than one year's duration.

Exposure of seed or plants to low temperature to induce or accelerate the development of the ability to form flowers.

The name given to the foehn in western North America, especially on the plains to the lee or eastern side of the Rocky Mountains in the United States and Canada.

On the eastern slopes of the Rocky Mountains the chinook generally blows from the west or southwest, although the direction may be modified by topography. Often the chinook begins to blow at the surface as an arctic front retreats to the east, producing dramatic temperature rises. Jumps of 10°–20°C can occur in 15 minutes, and at Havre, Montana, a jump from -12° to +5°C in 3 minutes was recorded.

The perceptually dominant wavelength of light from green thunderstorms ranges from blue-green to yellow-green. The purity of the color is generally low and the physical mechanism that causes the green appearance is not understood. Although green clouds often occur in conjunction with severe weather, there is no evidence to support anecdotal attributions of the cause of this green to specific characteristics of severe storms, such as hail or tornadoes.

(Photo by NOAA on Unsplash)

A widespread convectively induced straight-line windstorm.

Specifically, the term is defined as any family of particularly damaging downburst clusters produced by a mesoscale convective system. Such systems have sustained bow echoes with book-end vortices and/or rear-inflow jets and can generate considerable damage from straight-line winds. Damage must be incurred either continuously or intermittently over a swath of at least 650 km (~400 mi) and a width of approximately 100 km (~60 mi) or more.

The presence of substances in the atmosphere, particularly those that do not occur naturally.

These substances are generally contaminants that substantially alter or degrade the quality of the atmosphere. The term is often used to identify undesirable substances produced by human activity, that is, anthropogenic air pollution. Air pollution usually designates the collection of substances that adversely affects human health, animals, and plants; deteriorates structures; interferes with commerce; or interferes with the enjoyment of life.

A heat index that relates the development of plants, insects, and disease organisms to environmental air temperature.

GDD is calculated by subtracting a base temperature from the daily mean temperature and GDD values less than zero are set to zero. The summation over time is related to development of plants, insects, and disease organisms. The reference temperature (base temperature) below which development either slows or stops is species dependent. For example, cool season plants (canning pea, spring wheat, etc.): base temperature is 40°F (5°C); warm season plants (sweet corn, green bean, etc.): base temperature is 50°F (10°C); and very warm season plants (cotton, okra, etc.): base temperature is 60°F (15°C).

A halo in the form of a pillar of light extending above or below the sun and usually seen when the sun is low in the sky.

It is explained by reflection by the sides of columnar ice crystals falling with their long axes horizontal. The term light pillar is sometimes used when the source of light is artificial.

A squall or thunderstorm in the Mediterranean

Any storm that produces hailstones that fall to the ground; usually used when the amount or size of the hail is considered significant.

(Abbreviated PSC; also called nacreous clouds, mother-of-pearl clouds; rarely, luminous clouds.) Clouds are cirrus or altocumulus lenticularis, and show very strong irisation similar to that of mother-of-pearl, especially when the sun is several degrees below the horizon.

An exceptionally hot air mass that develops when high pressure aloft prevents warm air below from rising, thus trapping the warm air as if it were in a dome. The subsidence associated with the high pressure also causes further warming by compression. Heat domes are often associated with calm upper-level flow directly overhead and/or with blocking patterns.

The North Atlantic Oscillation (NAO) refers to a redistribution of atmospheric mass between the Arctic and subtropical Atlantic, manifesting as a north–south seesaw in the North Atlantic sea level pressure and geopotential height fields. The NAO is one of the dominant patterns of Northern Hemisphere climate variability, with significant impacts across much of North America, North Africa, Eurasia, and the Arctic.

A recirculation system between the South Equatorial Current and the North Equatorial Countercurrent in the extreme west of the Pacific Ocean, east of Halmahera. 

The circulation, about 1000 km in diameter, is clockwise from April–November but reverses during December–March when the Philippines experience monsoon winds blowing from the northeast in the Northern Hemisphere and from the northwest south of the equator.