There are 16 names in this directory beginning with the letter O.Obscuration
Any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere.
Occluded Front
A complex frontal system that occurs when a cold front overtakes a warm front. Also known as an occlusion.
Offshore Breeze
A wind that blows from the land towards a body of water. Also known as a land breeze.
Omega
A term used to describe vertical motion in the atmosphere. The "omega equation" used in numerical weather models is composed of two terms, the "differential vorticity advection" term and the "thickness advection" term. Put more simply, omega is determined by the amount of spin (or large scale rotation) and warm (or cold) advection present in the atmosphere. On a weather forecast chart, high values of omega (or a strong omega field) relate to upward vertical motion in the atmosphere. If this upward vertical motion is strong enough and in a sufficiently moist airmass, precipitation results.
Orographic Lift
The lifting of air as it passes over terrain features such hills or mountains. This can create orographic clouds and/or precipitation.
Outflow Boundary
A storm- scale or mesoscale boundary separating thunderstorm- cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature.
Overrunning
A condition that exists when a relatively warm air mass moves up and over a colder and denser air mass on the surface. The result is usually low clouds, fog and steady, light precipitation.
Overshooting Top (or Penetrating Top)
A dome- like protrusion above a thunderstorm anvil, representing a very strong updraft and hence a higher potential for severe weather with that storm.
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Obscuration
Any phenomenon in the atmosphere, other than precipitation, that reduces the horizontal visibility in the atmosphere.
Occluded Front
A complex frontal system that occurs when a cold front overtakes a warm front. Also known as an occlusion.
Offshore Breeze
A wind that blows from the land towards a body of water. Also known as a land breeze.
Omega
A term used to describe vertical motion in the atmosphere. The "omega equation" used in numerical weather models is composed of two terms, the "differential vorticity advection" term and the "thickness advection" term. Put more simply, omega is determined by the amount of spin (or large scale rotation) and warm (or cold) advection present in the atmosphere. On a weather forecast chart, high values of omega (or a strong omega field) relate to upward vertical motion in the atmosphere. If this upward vertical motion is strong enough and in a sufficiently moist airmass, precipitation results.
Orographic Lift
The lifting of air as it passes over terrain features such hills or mountains. This can create orographic clouds and/or precipitation.
Outflow Boundary
A storm- scale or mesoscale boundary separating thunderstorm- cooled air (outflow) from the surrounding air; similar in effect to a cold front, with passage marked by a wind shift and usually a drop in temperature.
Overrunning
A condition that exists when a relatively warm air mass moves up and over a colder and denser air mass on the surface. The result is usually low clouds, fog and steady, light precipitation.
Overshooting Top (or Penetrating Top)
A dome- like protrusion above a thunderstorm anvil, representing a very strong updraft and hence a higher potential for severe weather with that storm.