Observation(OB-ser-VAY-shun) Closely monitoring a patient's condition but withholding treatment until symptoms appear or change.
Observation WellA hole used to observe the ground-water surface at atmospheric pressure within soil or rock.
Observational networkObservational network A group of stations (surface meteorological, upper-air, or other stations) spread over a given area for making regular observations.
Occluded FrontA composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front.
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…
OceanographyThe study of the ocean, embracing and integrating all knowledge pertaining to the ocean's physical boundaries, the chemistry and physics of sea water, and…
OCFNTOccluded Front - a composite of two fronts, formed as a cold front overtakes a warm or quasi-stationary front.
OEODMThe Office of Equal Opportunity and Diversity Management. Provides a duel role.
Office of Global ProgramsThe Office of Global Programs (OGP) sponsors focused scientific research, within approximately eleven research elements, aimed at understanding climate…
Offshore BreezeA wind that blows from the land towards a body of water. Also known as a land breeze.
Offshore FlowOccurs when air moves from land to sea, and is usually associated with dry weather.
Offshore WatersThat portion of the oceans, gulfs, and seas beyond the coastal waters extending to a specified distance from the coastline, to a specified depth contour…
Offshore Waters Forecast(OFF) - A National Weather Service marine forecast product for that portion of the oceans, gulfs, and seas beyond the coastal waters extending to a…
OilDefined as oil of any kind or in any form including, but not limited to, petroleum, fuel oil, sludge, oil refuse, and oil mixed with wastes.
Oil shaleUnderground formation of a fine-grained sedimentary rock containing varying amounts of kerogen, a solid, waxy mixture of hydrocarbon compounds.
OktaUsed for the measurement of total cloud cover. One okta of cloud cover is the equivalent of 1/8 of the sky covered with cloud.
OmegaA term used to describe vertical motion in the atmosphere. The "omega equation" used in numerical weather models is composed of two terms, the…
Omega HighA warm high aloft which has become displaced and is on the polarward side of the jet stream.
Onshore BreezeA wind that blows from a body of water towards the land. Also known as a seabreeze
Onshore FlowOccurs when air moves from sea to land, and is usually associated wtih increased moisture.
OpaqueA condition where a material, such as a cloud, blocks the passage of radiant energy, especially light.
OPCOcean Prediction Center (Formally the Marine Prediction Center. An NCEP center which produces marine forecasts north of 30oN.
Open Lakes Forecast(GLF) - A National Weather Service marine forecast product for the U.S. waters within a Great Lake not including the waters covered by an existing…
Operational ProductsA product that has been fully tested and evaluated and is produced on a regular and ongoing basis.
optical depthA measure of how much light airborne particles, whether aersols, cloud droplets, or ice particles, prevent from passing through a column of atmosphere.
orbital cyclesvariations in the Earth's orbit around the sun with periods of 23,000 (precession of the equinoxes), 41,000 (obliquity), and 100,000 years (eccentricity).
OreRock or earth containing workable quantities of a mineral or minerals of commercial value.
Organic compoundAn organic compound contains carbon chemically bound to hydrogen. Organic compounds often contain other elements (particularly O, N, halogens, or S).
Organic fertilizerOrganic material such as manure or compost, applied to cropland as a source of plant nutrients.
OrificeAn opening with a closed perimeter and a regular form through which water flows.
OrographicRelated to, or caused by, physical geography (such as mountains or sloping terrain).
Orographic LiftingSame as Upslope Flow; occurs when air is forced to rise and cool due to terrain features such as hills or mountains.
Orographic PrecipitationPrecipitation which is caused by hills or mountain ranges deflecting the moisture-laden air masses upward, causing them to cool and precipitate their…
Orographic UpliftSame as Orographic Lifting; occurs when air is forced to rise and cool due to terrain features such as hills or mountains.
Orographic WavesA wavelike airflow produced over and in the lee of a mountain barrier.
Orphan AnvilSlang for an anvil from a dissipated thunderstorm, below which no other clouds remain.
OscillationA shift in position of various high and low pressure systems that in climate terms is usually defined as an index (i.e.
ostracoda small crustacean that lives in either the ocean or in freshwater.
Outer Convective BandBands in a hurricane that occur in advance of main rain shield and up to 300 miles from the eye of the hurricane.
OutflowThe volume of growing cells that is removed from a bioreactor during a continuous fermentation process.
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…
Outflow ChannelA natural stream channel which transports reservoir releases.
Outgoing Longwave RadiationOutgoing Longwave Radiation is a polar satellite derived measurement of the radiative character of energy radiated from the warmer earth surface to cooler…
OutletAn opening through which water can be freely discharged from a reservoir to the river for a particular purpose.
Outlet Discharge StructureProtects the downstream end of the outlet pipe from erosion and is often designed to slow down the velocity of released water to prevent erosion of the…
OutlookUbiquitous Microsoft personal information management (PIM) program, which includes email, task management and a calendar.
OVCOvercast- An official sky cover classification for aviation weather observations, when the sky is completely covered by an obscuring phenomenon.
OvercastTo cast a lure, fly or bait beyond the aimed-for target.
Overland FlowThe flow of rainwater or snowmelt over the land surface toward stream channels. After it enters a watercourse it becomes runoff.
OverrunningA weather pattern in which a relatively warm air mass is in motion above another air mass of greater density at the surface.
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…
OxidizeTo chemically transform a substance by combining it with oxygen.
Oxygen cycleCyclic movement of oxygen in different chemical forms from the environment, to organisms, and then back to the environment.
oxygen isotope ratio (δ<sup>18</sup>O)an expression for the ratio of the two isotopes 18O to 16O in a sample relative to a standard, defined as: δ18O= (18O/16Osample - 18O/16Ostandard)/…
OzoneTropospheric ozone (ground-level ozone), or smog, is formed when volatile organic compounds, oxygen and nitrogen oxides react in the presence of sunlight.
Ozone (O3)A strong-smelling, reactive, toxic, chemical gas consisting of three oxygen atoms chemically attached to each other.
Ozone (O<sub>3</sub>)A colorless gas with a pungent odor, having the molecular form of O3 , found in two layers of the atmosphere, the stratosphere (about 90% of the total…
Ozone Action DayA "heads-up" message issued by the Department of Natural Resources (DNR) through the National Weather Service when ozone levels may reach dangerous levels…
Ozone AdvisoryIt is issued by the Department of Natural Resources (DNR) through the National Weather Service when ozone levels reach 100.
Ozone Depleting Substance (ODS)A family of man-made compounds that includes, but are not limited to, chlorofluorocarbons (CFCs), bromofluorocarbons (halons), methyl chloroform, carbon…
Ozone HoleA severe depletion of stratospheric ozone over Antarctica that occurs each spring. The possibility exists that a hole could form over the Arctic as well.
Ozone LayerAn atmospheric layer that contains a high proportion of oxygen that exists as ozone.
Ozone PrecursorsChemical compounds, such as carbon monoxide, methane, non-methane hydrocarbons, and nitrogen oxides, which in the presence of solar radiation react with…
Ozone shieldOzone shield Stratospheric ozone layer, giving protection to the Earth's surface due to intense absorption of harmful solar ultraviolet radiation by the…