Weather Glossary - O
Search
Occluded mesocycloneA mesocyclone in which air from the rear-flank downdraft has completely enveloped the circulation at low levels, cutting off the inflow of warm unstable low-level air. |
OcclusionA frontal system which forms when a cold front overtakes a warm front. When the air behind the front is cooler than the air ahead, it is called a cold occlusion, when the air ahead is milder, it is a warm occlusion. |
OffshoreThe coastal water zone seaward of inshore waters. |
OrographicRelated to, or caused by, physical geography (such as mountains or sloping terrain). |
Orographic liftLifting of air caused by its passage up and over mountains or other sloping terrain. |
Orographic rainPrecipitation that results from Orographic lift |
Orphan anvil[Slang] An anvil from a dissipated thunderstorm, below which no other clouds remain. |
Outflow boundaryA 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. Outflow boundaries may persist for 24 hours or more after the thunderstorms that generated them dissipate, and may travel hundreds of kilometres from their area of origin. New thunderstorms often develop along outflow boundaries, especially near the point of intersection with another boundary (cold front, dry line, another outflow boundary, etc.; see triple point). |
OvercastDescribes cloud cover when 8/8ths of the sky is covered in cloud. |
OverhangRadar term indicating a region of high reflectivity at middle and upper levels above an area of weak reflectivity at low levels. (The latter area is known as a weak-echo region, or WER.) The overhang is found on the inflow side of a thunderstorm (normally the south or southeast side). See BWER. |
OverrunningA weather pattern in which a relatively warm air mass is in motion above another air mass of greater density at the surface. Embedded thunderstorms sometimes develop in such a pattern; severe thunderstorms (mainly with large hail) can occur, but tornadoes are unlikely. |
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. A persistent and/or large overshooting top (anvil dome) often is present on a supercell. A short-lived overshooting top, or one that forms and dissipates in cycles, may indicate the presence of a pulse storm or a cyclic storm. See HP storm, LP storm, and supercell. |
OxygenThe second most abundant gas in air, comprising 21% by volume. It is a colourless and odourless gas. |
OzoneOne of several gases that make up the Earth's atmosphere. It is the triatomic form of oxygen and makes up approximately one part in three million of all of the gases in the atmosphere. If all the ozone contained in the atmosphere from the ground level up to a height of 60 km could be assembled at the earth's surface, it would comprise a layer of gas only about 3 millimetres thick. Ozone is toxic at high concentrations because it reacts strongly with other molecules. |
-
Display your Local Weather here
automatically each time you visit us:
Rotates through Temperature,
Wind, Humidity and RainUse the Search Bar above
to find your Local, and go to the Local page
Click "Set My Local"
button next to the location name
Weather News
Victoria weather: BOM forecasts heavy rain and storms after hot night in Melbourne
09:59 EDT
Heavy rain and storms are forecast for Victoria today after a sweltering night in Melbourne, with the authorities issuing a warning about flash flooding.
NSW weather: Extreme heatwave forecast to bring sizzling end to 2016
09:47 EDT
State government agencies have activated a heatwave action plan, with soaring temperatures across most of New South Wales set to cap off 2016.
SA storms: Power cut to 34,000 as crews repair damages from severe weather
09:42 EDT
About 34,000 South Australian properties remain without power after a day of wild storms, with SA Power Networks saying it had sought help from interstate to restore electricity supplies.
