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CPC - Climate Prediction Centre Category: Meteorology and astronomy > Climate and Weather Glossary Date & country: 26/11/2008, USA Words: 106

Hazards Assessment
CPC's Hazards Assessment provides emergency managers, planners, forecasters and the public advance notice of potential hazards related to climate, weather and hydrological events.

Greenhouse Gas
Certain gases, such as water vapor, carbon dioxide, and methane, that more effectively trap heat affecting the Earth's surface temperature.

Growing Degree Days
A heat index that relates the development of plants, insects, and disease organisms to environmental air temperature. The index varies depending on whether it is a cool, warm, or very warm season plant. For example, a corn growing degree day (GDD) is an index used to express crop maturity. The index is computed by subtracting a base temperature of 50oF from the average of the maximum and minimum t...

GMT
Greenwich Mean Time

Greenhouse Effect
The atmosphere allows solar radiation to reach the earth relatively easily. The atmosphere absorbs the infrared radiation emitted by the Earth's surface and radiates it back to the Earth in much the same way a greenhouse traps heat as the sun's rays pass through the glass, and the heat generated does not pass back through the glass. The 'greenhouse effect' causes the surface of the Earth to be...

Global Warming
Certain natural and human-produced gases prevent the sun's energy from escaping back to space leading to an overall rise in the temperature of the Earth's atmosphere.

GCMs
(General Circulation Models)These computer simulations reproduce the Earth's weather patterns and can be used to predict change in the weather and climate.

Forecasts
(Synonymous with predictions and outlooks)A weather forecast, or prediction, is an estimation based on special knowledge of the future state of the atmosphere with respect to temperature, precipitation, and wind. Weather forecasts are now routinely provided for up to 14 days in advance and outlooks for seasonal and longer timescales.

Extratropical
In meteorology, the area north of the Tropic of Cancer and the area south of the Tropic of Capricorn. In other words, the area outside the tropics.

Experimental Products
An experimental product is in the final stages of testing and evaluation. If the product proves accurate and valuable to users then the next step is to make it an operational product.

Excessive Heat Outlook
This CPC product, a combination of temperature and humidity over a certain number of days, is designed to provide an indication of areas of the country where people and animals may need to take precautions against the heat during May to November. (See http://www.cpc.ncep.noaa.gov/products/predictions/hi_307.html)

Evaporation
The physical process by which a liquid or solid is changed to a gas; the opposite of condensation.

ENSO Diagnostic Discussion
The CPC issues the ENSO Diagnostic Discussion around the middle of the month. The discussion addresses the current oceanic and atmospheric conditions in the Pacific and the seasonal climate outlook for the following one to three seasons. (See http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/)

ENSO
(El Niño-Southern Oscillation)Originally, ENSO referred to El Niño/ Southern Oscillation, or the combined atmosphere/ocean system during an El Niño warm event. The ENSO cycle includes La Niña and El Niño phases as well as neutral phases, or ENSO cycle, of the coupled atmosphere/ocean system though sometimes it is still used as originally defined. The Southern Oscillation is quantified by the South...

Ensemble Forecast
Multiple predictions from an ensemble of slightly different initial conditions and/or various versions of models. The objectives is to improve the accuracy of the forecast through averaging the various forecasts, which eliminates non-predictable components, and to provide reliable information on forecast uncertainties from the diversity amongst ensemble members. Forecasters use this tool to measur...

El Niño
El Niño, a phase of ENSO, is a periodic warming of surface ocean waters in the eastern tropical Pacific along with a shift in convection in the western Pacific further east than the climatological average. These conditions affect weather patterns around the world. El Niño episodes occur roughly every four-to-five years and can last up to 12-to-18 months. The preliminary CPC definition of El Niño i...

Drought Assessments
At the end of each month, CPC issues a long-term seasonal drought assessment. On Thursdays of each week, the CPC together with NOAA National Climatic Data Center, the United States Department of Agriculture, and the National Drought Mitigation Center in Lincoln, Nebraska, issues a weekly drought assessment called the United States Drought Monitor. These assessments review national drought conditio...

Drought
Drought is a deficiency of moisture that results in adverse impacts on people, animals, or vegetation over a sizeable area. NOAA together with its partners provides short- and long-term Drought Assessments.

Doppler radar
Radar that measures speed and direction of a moving object, such as water or ice particles, birds, and insects.

Dobson Unit
Unit used to measure the abundance of ozone in the atmosphere. One Dobson unit is the equivalent of 2.69 x 1016 molecules of ozone/cm2.

Dew Point
The point at which the air at a certain temperature contains all the moisture possible without precipitation occurring. When the dew point is 65oF, one begins to feel the humidity. The higher the temperature associated with the dew point, the more uncomfortable one feels.

Decadal
A consecutive ten year period.

Degree Day
For any individual day, degree days indicate how far that day's average temperature departed from 65oF. Heating Degree Days measure heating energy demand. It is a measure to indicate how far the average temperature fell below 65oF. Similarly, Cooling Degree Days's, which measure cooling energy demand, indicate how far the temperature averaged above 65oF. In both cases, smaller values represent l...

Cyclone
In general use the term cyclone is applied to any storm, especially violent, small scale circulations such as tornados, waterspouts, and dust devils. In meteorology, the term refers to a type of atmospheric disturbance centered around a low-pressure center that often results in stormy weather. In common practice the term cyclone, and low, are used interchangeably and are frequently referred to as ...

Coupled Model
In the context of climate modeling this usually refers to a numerical model which simulates both atmospheric and oceanic motions and temperatures and which takes into account the effects of each component on the other.

Crop Moisture Index
In 1968, Palmer developed the index to assess short-term crop water conditions and needs across major crop-producing regions. This index is a useful tool in forecasting short-term drought conditions. (See Palmer Drought Severity & Crop Moisture Indices)

Cooling Degree Days
A form of degree-day used to estimate energy requirements for air conditioning or refrigeration.

CONUS
Continental United States

Convection
Transfer of heat by fluid motion between two areas with different temperatures. In meteorology, the rising and descending air motion caused by heat. Atmospheric convection is almost always turbulent and is the dominant vertical transport process over tropical oceans and during sunny days over continents. The terms 'convection' and 'thunderstorms' are often use interchangeably, although thunder...

Condensation
The physical process by which water vapor in the atmosphere changes to liquid in the form of dew, fog or cloud; the opposite of evaporation.

Composite
An average that is calculated according to specific criteria. For example, one might want a composite for the rainfall at a given location for all years where the temperature was much above average.

Climatology
(1) The description and scientific study of climate. (2) A quantitative description of climate showing the characteristic values of climate variables over a region.

Climatological Outlook
An outlook based upon climatological statistics for a region, abbreviated as CL on seasonal outlook maps. CL indicates that the climate outlook has an equal chance of being above normal, normal, or below normal.

Climate Test Bed
The Climate Test Bed is an NCEP project, led by CPC in close collaboration with EMC and open to the climate community inside and outside NOAA. Its mission is to accelerate the transition of research and development into improved NOAA operational climate forecasts, products, and applications. It will support and promote: exchange of climate forecast system software among NCEP, GFDL, NASA, NCAR, COL...

Climate System
The system consisting of the atmosphere (gases), hydrosphere (water), lithosphere (solid rocky part of the Earth), and biosphere (living) that determine the Earth's climate.

Climate Outlook
A climate outlook gives probabilities that conditions, averaged over a specified period, will be below-normal, normal, or above-normal.

Climate Prediction Center
This Center is one of several centers under the National Centers for Environmental Prediction (NCEP) part of the National Weather Service (NWS) in the National Oceanic and Atmospheric Administration (NOAA). The Center serves the public by assessing and forecasting the impacts of short-term climate variability, emphasizing enhanced risks of weather-related extreme events, for use in mitigating loss...

Climate Model
Mathematical model for quantitatively describing, simulating, and analyzing the interactions between the atmosphere and underlying surface (e.g., ocean, land, and ice).

Climate Diagnostics Center
The mission of NOAA's Climate Diagnostics Center is to identify the nature and causes for climate variations on time scales ranging from a month to centuries. (See http://www.cdc.noaa.gov)

Climate Diagnostics Bulletin
The monthly CPC Bulletin reports on the previous months' status of the ocean-atmosphere climate system and provides various seasonal ENSO-related outlooks. It is issued by the fifteenth of the month. (See http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/bulletin/)

Climate Change
A non-random change in climate that is measured over several decades or longer. The change may be due to natural or human-induced causes.

Climate
The average of weather over at least a 30-year period. Note that the climate taken over different periods of time (30 years, 1000 years) may be different. The old saying is climate is what we expect and weather is what we get.

CL
An abbreviation used on climate outlook maps to indicate areas where equal chances of experiencing below-normal, normal, or above-normal conditions are possible.

Circulation
The flow, or movement, of a fluid (e.g., water or air) in or through a given area or volume.

Chlorofluorocarbons
Manufactured substances used as coolants and computer-chip cleaners. When these products break down they destroy stratospheric ozone, creating the Antarctic Ozone Hole in the Southern Hemisphere spring (Northern Hemisphere fall). While no longer in use, their long lifetime will lead to a very slow removal from the atmosphere.

Atmospheric Circulation Model
A mathematical model for quantitatively describing, simulating, and analyzing the structure of the circulation in the atmosphere and the underlying causes. Sometimes referred to as Atmospheric General Circulation Models or AGCMs (See GCMs)

Apparent temperature
The temperature people perceive under hot and humid conditions. (See Excessive Heat Outlook).

Arctic Oscillation (AO)
The Arctic Oscillation is a pattern in which atmospheric pressure at polar and middle latitudes fluctuates between negative and positive phases. The negative phase brings higher-than-normal pressure over the polar region and lower-than-normal pressure at about 45 degrees north latitude. The negative phase allows cold air to plunge into the Midwestern United States and western Europe, and storms br...

Anomaly
The deviation of a measurable unit, (e.g., temperature or precipitation) in a given region over a specified period from the long-term average, often the thirty year mean, for the same region.

Heating Degree Days
A form of degree-day used to estimate energy requirements for heating.

HectoPascals (hPa)
1 hPA= 1 millibar, a unit of pressure.

Hurricane
See Cyclone

Hydrology
The scientific study of precipitation, evaporation, distribution, and effects of water on the Earth's surface, in the soil and rocks, and in the atmosphere.

Intraseasonal Oscillations
Variability on a timescale less than a season. One example is the Madden-Julian Oscillation.

Jet Stream
Strong winds concentrated within a narrow zone in the atmosphere in the upper troposphere, about 30,000 feet aloft that generally move in an easterly direction that drive weather systems around the globe. In North America jet streams are more pronounced in winter.

Kelvin Waves
Fluctuations in wind speed at the ocean surface at the Equator result in eastward propagating waves, known as Kelvin Waves. Kelvin Waves cause variations in the depth of the oceanic thermocline, the boundary between warm waters in the upper ocean and cold waters in the deep ocean. They play an important role in monitoring and predicting El Niño episodes.

La Niña
La Niña, a phase of ENSO, is a periodic cooling of surface ocean waters in the eastern tropical Pacific along with a shift in convection in the western Pacific further west than the climatological average. These conditions affect weather patterns around the world. The preliminary CPC definition of La Niña is a phenomenon in the equatorial Pacific Ocean characterized by a negative sea surface tempe...

Long Wave
(or Planetary Wave)In meteorology, a long wave in atmospheric circulation in the major belt of westerlies has different characteristics than rapidly moving storms nearer the Earth's surface

Low Level Jet
A jet stream that is typically found in the lower 2-3 km, or approximately 6,000 to 9, 500 feet, of the troposphere.

Madden-Julian Oscillation
(MJO)Tropical rainfall exhibits strong variability on time scales shorter than the seasonal El Niño-Southern Oscillation (ENSO). These fluctuations in tropical rainfall often go through an entire cycle in 30-60 days, and are referred to as the Madden-Julian Oscillation or intraseasonal oscillations. The intraseasonal oscillations are a naturally occurring component of our coupled ocean-atmosphere ...

Mean
The arithmetic average, or the middle point between two extremes.

Meteorology
The scientific study of the physics, chemistry, and dynamics of the Earth's atmosphere, especially weather and climate.

Millibar
A pressure unit of 1000 dynes cm-2, often used for reporting atmospheric pressure where one millibar equals 1 hectopascal (hPA).

Monsoons
Seasonal winds. They are caused primarily by the greater annual variation in air temperature over large land surfaces compared to ocean surfaces though other factors like land-relief are important.

MRF
Medium Range Forecast, usually a reference to a numeric model that extends one to two weeks into the future.

MRF-Based 8-day Guidance
Based on the MRF model output statistics the Guidance gives a temperature forecast (max and min) with actual values (e.g. high of 50 low of 40) for the next 7 days plus probability of precipitation, and mean wind speed and cloudiness in easy-to-understand and use text format.

NAO
North Atlantic Oscillation

NAO Index
This index measures the anomalies in sea level pressure between the Icelandic low pressure system and the Azores high pressure system. When the difference is positive the northeastern United States sees an increase in temperature and a decrease in snow days; the central US has increased precipitation, the North Sea has an increase in storms; and Norway along with Northern Europe has warmer tempera...

National Climatic Data Center
(NCDC)NCDC maintains the world's largest active archive of weather data. NCDC produces numerous climate publications and responds to data requests from all over the world. (See http://www.ncdc.noaa.gov)

National Weather Service
(NWS)The National Weather Service (NWS) -provides weather, hydrologic, and climate forecasts and warnings for the United States, its territories, adjacent waters and ocean areas, for the protection of life and property and the enhancement of the national economy. NWS data and products form a national information database and infrastructure which can be used by other governmental agencies, the priv...

NCEP
National Centers for Environmental Prediction

NOAA
National Oceanic and Atmospheric Administration

Normal
To understand whether precipitation and temperature is above or below normal for seasons and longer timescales, normal is defined as the average weather over 30 years. These averages are recalculated every ten years. The National Weather Service has just recalculated the baseline period for normal from 1961 to 1990 to 1971 to 2000. Since the cool decade of the 1960's has been replaced with the mi...

North Atlantic Oscillation
The NAO is a large-scale fluctuation in atmospheric pressure between the subtropical high pressure system located near the Azores in the Atlantic Ocean and the sub-polar low pressure system near Iceland and is quantified in the NAO Index. The surface pressure drives surface winds and wintertime storms from west to east across the North Atlantic affecting climate from New England to western Europe ...

Numerical Forecasting
(Also called mathematical forecasting, dynamical forecasting, physical forecasting, and numerical weather prediction)A computer forecast or prediction based on equations governing the motions and the forces affecting motion of fluids. The equations are based, or initialized, on specified weather or climate conditions at a certain place and time.

NWS
National Weather Service

Office of Global Programs (OGP)
The Office of Global Programs (OGP) sponsors focused scientific research, within approximately eleven research elements, aimed at understanding climate variability and its predictability. Through studies in these areas, researchers coordinate activities that jointly contribute to improved predictions and assessments of climate variability over a continuum of timescales from season to season, year ...

OLR
Outgoing Longwave Radiation is a polar satellite derived measurement of the radiative character of energy radiated from the warmer earth surface to cooler space. This measurement provides information on cloud-top temperature which can be used to estimate tropical precipitation amounts which is important in forecasting weather and climate.

Operational Products
Products and data that have been fully tested and evaluated that are produced on a regular and ongoing basis.

Oscillations
A shift in position of various high and low pressure systems that in climate terms is usually defined as an index (i.e., a single numerically-derived number, that represents the distribution of temperature and pressure over a wide ocean area, such as the El Niño-Southern Oscillation, North Atlantic Oscillation, and Pacific Decadal Oscillation).

Ozone
A molecule consisting of three oxygen atoms that is formed by a reaction of oxygen and ultraviolet radiation. In the stratosphere, ozone has beneficial properties where it forms an ozone shield that prevents dangerous radiation from reaching the Earth's surface. Closer to the planet's surface, ozone is considered an air pollutant that adversely affects humans, plants and animals as well as a gre...

Ozone Hole
A severe depletion of stratospheric ozone over Antarctica that occurs each spring. The possibility exists that a hole could form over the Arctic as well. The depletion is caused by a chemical reaction involving ozone and chlorine, primarily from human produced sources, cloud particles, and low temperatures.

Pacific Decadal Oscillation
A recently described pattern of climate variation similar to ENSO though on a timescale of decades and not seasons. It is characterized by SST anomalies of one sign in the north-central Pacific and SST anomalies of another sign to the north and east near the Aleutians and the Gulf of Alaska. It primarily affects weather patterns and sea surface temperatures in the Pacific Northwest, Alaska, and no...

PRCP
Abbreviation for precipitation.

Probability
A chance, or likelihood, that a certain event might happen.

Relative humidity
An estimate of the amount of moisture in the air relative to the amount of moisture that the air can hold at a specific temperature. For example, if it's 70oF near dawn on a foggy summer morning, the relative humidity is near 100%. During the afternoon the temperature soars to 95oF and the fog disappears. The moisture in the atmosphere has not changed appreciably, but the relative humidity drops ...

Retrogression
or retrograde motion means motion that is backwards from the usual way things move in the Northern Hemisphere extratropics - which is from west to east. In meterology, the term is used in relation to atmospheric waves or pressure systems. When meterologists say that a pattern will retrograde, they mean that the troughs and ridges will end up further west than they were previously. Normal motion (o...

Sea Surface Temperatures (SSTs)
The term refers to the mean temperature of the ocean in the upper few meters.

SOI (Southern Oscillation Index)
SOI is based on the (atmospheric) pressure difference between Tahiti and Darwin, Australia. It is highly correlated with tropical sea surface temperature anomaly indices recorded in Niño3.

SSTs
Sea Surface Temperatures

Stratosphere
The region of the atmosphere extending from the top of the troposphere to the base of the mesosphere, an important area for monitoring stratospheric ozone.

Stratospheric ozone
In the stratosphere, ozone has beneficial properties where it forms an ozone shield that prevents dangerous radiation from reaching the Earth's surface. Recently, it was discovered that in certain parts of the world, especially over the poles, stratospheric ozone was disappearing creating an ozone hole.

Subtropical
A climate zone adjacent to the tropics with warm temperatures and little rainfall.

Synoptic scale
Used to classify large-scale weather systems more than 200 miles across.

Teleconnection
A strong statistical relationship between weather in different parts of the globe. For example, there appears to be a teleconnection between the tropics and North America during El Niño.

TEMP
Abbreviation for temperature, given in Fahrenheit for CPC products.

Thermocline
As one descends from the surface of the ocean, the temperature remains nearly the same as it was at the surface, but at a certain depth temperature starts decreasing rapidly with depth. This boundary is called the thermocline. In studying the tropical Pacific Ocean, the depth of 20oC water ('the 20oC isotherm') is often used as a proxy for the depth of the thermocline. Along the equator, the 20o...

Troposphere
The lowest portion of the atmosphere which lies next to the earth's surface where most weather occurs.

Typhoon
See Cyclone

Ultraviolet
(UV) (or Ultraviolet Radiation)Ultraviolet radiation from the sun plays a role in the formation of the ozone layer by acting as a catalyst for a chemical reaction that breaks apart oxygen molecules which then recombine to form ozone. The absorption of UV by stratospheric ozone and atmospheric oxygen prevents very little ultraviolet radiation to reach earth's surfaces where it can detrimental effe...