Glossary[ A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z] atmospheric pressure/barometric pressureAtmospheric Pressure, also called barometric pressure, is the force per unit area exerted by the atmosphere as a consequence of its weight. It is equal to the weight of a vertical column of air of a unit area, extending from a given elevation or level to the outer limit of the atmosphere. Measurement units for pressure are called hectopascals (hPa).
blowing dustDust that is raised by the wind to moderate heights above the ground. Visibility at eye level may be reduced to 1 km. blowing snowSnow particles violently stirred up by wind to sufficient heights above the ground to reduce visibility to 10 km or less.
calmAn absence of wind flow or any other air motion. celsiusA temperature scale where water at sea level has a freezing point of 0°C (Celsius) and a boiling point of +100°C. Commonly used in countries that observe the metric system of measurement. Created by Anders Celsius in 1742. In 1948, the Ninth General Conference on Weights and Measures replaced "degree centigrade" with "degree Celsius." To convert from degrees Celsius to degrees Fahrenheit, (C * 9/5) + 32 climateThe historical record and description of average daily and in seasonal weather events that help describe a region. Statistics are generally drawn over several decades. Climatology, or the study of climate, includes climatic data, the analysis of the causes of the differences in climate, and the application of climatic data to the solution of specific design or operational problems. It differs from weather, which is concerned with short term or instantaneous variations in the state of the atmosphere at a specific time. CLIMATE ID, STATION ID, STATION NUMBERAlso referred to as station ID or station number, the Climate ID is a 7 digit number assigned by the Meteorological Service of Canada to a site where official weather observations are taken, and serves as a permanent, unique identifier. The first digit assigned identifies the province where the second and third digits identify the climatological district within the province. When observations are discontinued at a site, the number is not used for subsequent stations (which may, or may not, differ in name) unless it is judged that the records from the earlier and subsequent stations may be combined for most climatological purposes. cloudA visible collection of minute particle matter, such as water droplets and/or ice crystals, in the air. A cloud forms in the atmosphere as a result of condensation of water vapour. Condensation nuclei, such as smoke or dust particles, form a surface upon which water vapour can condense. CODE for NORMALSNormals for some elements are derived from less than 30 years of record but can still be considered useful. The minimum number of years used are indicated by a "code" defined as:
cooling degree-daysA cooling degree-day is given for each degree that the daily mean temperature departs above the baseline of 18 degrees Celsius. (i.e. Mean temperature - 18). It is used to estimate energy requirements and is an indication of fuel consumption for air conditioning or refrigeration (cooling).
Data IntervalDepending on individual climate observing programs and climate element, weather observations at a climate station are recorded at three basic intervals:
degree-daysDegree-days for a given day represent the number of Celsius degrees that the mean temperature is above or below a given base temperature. For example, heating degree-days are the number of degrees below 18° C. If the temperature is equal to or greater than 18, then the number will be zero. Values above or below the base of 18° C are used primarily to estimate the heating and cooling requirements of buildings. Values above 5° C are frequently called growing degree-days, and are used in agriculture as an index of crop growth. dew point (°C)The dew point temperature in degrees C, a measure of the humidity of the air, is the temperature to which the air would have to be cooled to reach saturation with respect to liquid water. Saturation occurs when the air is holding the maximum water vapour possible at that temperature and atmospheric pressure. direction of maximum gust (10's Deg)The direction of the maximum gust (true or geographic, not magnetic) from which the wind blows. Expressed in ten's of degrees (10's Deg), 9 means 90 degrees true or an east wind, and 36 means 360 degrees true or a wind blowing from the geographic north pole. This value is not reported for a day if the maximum speed does not exceed 30 km/h. drizzleFairly uniform precipitation composed of fine drops of water (diameter < 0.5 mm). Drizzle drops are too small to cause appreciable ripples on the surface of still water. The drops appear almost to float in the air, thus making visible even slight movements of air. dry bulb temperatureThe dry bulb temperature is the value taken from a thermometer when the bulb of the thermometer is dry. It reflects the ambient temperature independent on the moisture content of the air.
elevation (m)The elevation in metres (m) refers to the elevation of the observing location above mean sea level. The elevation of each site is given to the nearest metre and is generally the height of ground on which the instruments are exposed. Prior to April 1, 1986, the elevation at principal stations located at airports was generally the established by the elevation of the aerodrome. For principal stations not located at airports the elevation was established by the elevation of the barometer cistern. evaporationThe physical process by which a liquid, such as water is transformed into a gaseous state, such as water vapour. It is the opposite physical process of condensation. Evaporation refers to the calculated lake evaporation occurring from a small natural open water-body having negligible heat storage and very little heat transfer at its bottom and sides. It represents the water loss from ponds and small reservoirs but not from lakes that have large hear storage capacities. Lake Evaporation is calculated using the observed daily values of pan evaporative water loss, the mean temperatures of the water in the pan and of the nearby air, and the total wind run over the pan.
fogA visible aggregate of minute water droplets suspended in the air at or near the surface of the earth, reducing horizontal visibility to less than 1 km. It is created when the temperature and the dew point of the air have become the same, or nearly the same. It is rarely observed when the temperature and dew point differ by more than 2° C. freezing drizzleDrizzle, the drops of which freeze on impact with the ground or with objects at or near the ground. freezing rainRain, the drops of which freeze on impact with the ground or with objects at or near the ground. frostFrost is the condition that exists when the temperature of the air near the earth or earth-bound objects falls to freezing or lower (0° C). Alternately, frost or hoar frost describes a deposition of ice crystals on objects by direct sublimation of water vapour from the air.
gustsGusts are sudden, rapid and brief changes in the wind speed. They are characterized by more or less continual fluctuations between the high (peak) and low (lull) speed. The extreme gust speed is the instantaneous peak wind observed from the anemometer dials, abstracted from a continuous chart recording, or from a data logger.
hailPrecipitation of small balls or pieces of ice with a diameter ranging from 5 to 50 mm or more. Hail is generally observed during heavy thunderstorms. heating degree-dayOne heating degree-day is given for each degree that the daily mean temperature is below 18° Celsius. (i.e. 18 - Mean temperature). It is used to estimate energy requirements and is an indication of fuel consumption for heating. HUMIDEXHumidex is an index to indicate how hot or humid the weather feels to the
average person. It is derived by combining temperature and humidity values
into one number to reflect the perceived temperature. The standard Humidex formula used by Environment Canada is: humidex = (air temperature) + h where dewpoint is expressed in kelvins (temperature in K = temperature in °C + 273.1) and 5417.7530 is a rounded constant based on the molecular weight of water, latent heat of evaporation, and the universal gas constant
iceThe solid form of water. It can be found in the atmosphere in the form of ice crystals, snow, ice pellets, and hail for example. ice crystalsPrecipitation in the form of slowly falling, singular or unbranched ice needles, columns, or plates. They make up cirriform clouds, frost, and ice fog. Also, they produce optical phenomena such as halos, coronas, and sun pillars. May be called "diamond dust." Precipitation of ice crystals in the form of needles, columns or plates sometimes so tiny, they seem suspended in air. They are mainly visible when they glitter in sunshine and occur only at very low temperatures and stable air masses. ice fogA type of fog composed of suspended particles of ice or ice crystals 20 to 100 microns resulting from the freezing of tiny supercooled water droplets. Ice fog occurs in clear, calm, stable air when temperatures are < -30° C. ice pelletsPrecipitation of transparent or translucent pellets of ice, which are spherical or irregular shaped, having a diameter of 5 mm or less. They are classified into two types: hard grains of ice consisting of frozen rain drops or largely melted and refrozen snowflakes; pellets of snow encased in a thin layer of ice which have formed from the freezing of droplets intercepted by pellets or water resulting from the partial melting of pellets. Ice pellets usually bounce when hitting hard ground and make a sound on impact. They can fall as continuous precipitation or in showers.
Local Standard TimeThe Local Standard Time is used for observation purposes and is that of the standard time zone in which the station is located, whether or not "daylight saving time" is adopted for other purposes. In Canada, Local Standard Time is commonly used for archiving surface weather observations. latitudeThe location north or south in reference to the equator, which is designated at zero (0) degrees. Parallel lines that circle the globe both north and south of the equator. The poles are at 90° North and South latitude. Latitude and longitude co-ordinates for climate stations are generally for the instrument site; however prior to April 1, 1986 at principal stations (airports) the locations given were normally the official airport locations. The accuracy of these locations depended on the quality of the reference maps available at the time. The latitude and longitude of each site is given to the nearest minute or to the nearest 0.02 of a degree. All locations in Canada are north of the equator. longitudeThe location east or west in reference to the Prime Meridian, which is designated as zero (0) degrees longitude. The distance between lines of longitude are greater at the equator and smaller at the higher latitudes, intersecting at the earth's North and South Poles. Time zones are correlated to longitude. Latitude and longitude co-ordinates for climate stations are generally for the instrument site; however prior to April 1, 1986 at principal stations (airports) the locations given were normally the official airport locations. The accuracy of these locations depended on the quality of the reference maps available at the time. Negative values of longitude denote degrees west of the Greenwich Meridian. All locations in Canada have negative values of longitude.
maximum temperature (°C)This is the highest or hottest temperature in degrees Celsius (°C) observed at a specified location for a specified time interval. minimum temperature (°C)rainThis is the lowest or coldest temperature in degrees Celsius (°C) observed at a specified location for a specified time interval. maximum relative humidity (%)The maximum percentage (%) value of all hourly relative humidity values observed at a specified location for a specified time interval. minimum relative humidity (%)The minimum percentage (%) value of all hourly relative humidity values observed at a specified location for a specified time interval. mean sea level pressureThe atmospheric pressure at mean sea level usually determined from the observed station pressure. Mean sea level pressure is computed from the station pressure and reported so that the barometric pressures at stations of different elevations can be compared at a common level for analysis purposes. mean temperature (°C)The average of temperature readings taken over a specified amount of time. For example, daily mean temperatures are calculated from the sum of the maximum and minimum temperatures for the day, divided by 2.
number of days with specified parametersThese tables give the average number of days per month or year on which a
specific meteorological event occurs.
peak gustThe highest instantaneous wind speed observed or recorded. precipitationAny and all forms of water, liquid or solid, that falls from clouds and reaches the ground. This includes drizzle, freezing drizzle, freezing rain, hail, ice crystals, ice pellets, rain, snow, snow pellets, and snow grains. Types of precipitation that originate aloft are classified under Liquid Precipitation, Freezing Precipitation and Frozen Precipitation. The measurement of precipitation is expressed in terms of vertical depth of water (or water equivalent in the case of solid forms) which reaches the ground during a stated period. The millimetre (mm) is the unit of measurement of liquid precipitation and the vertical depth of water or water equivalent is express to the nearest 0.2 mm. Less than 0.2 mm is called a "Trace". Snow depth is measured to the nearest 0.2 cm. Less than 0.2 cm is called a "Trace".
radiationThe process by which energy is propagated through any medium by virtue of the wave motion of that medium. Electromagnetic radiation, which emits heat and light, is one form. Sound waves are another. Radiation values are recorded hourly in Local Apparent Time and the units
are expressed in megajoules per square metre, except daylight illumination
is in 1000 lumen-hours per square metre. rainPrecipitation in the form of liquid water droplets greater than 0.5 mm. If widely scattered, the drop size may be smaller. The intensity of rain is based on rate of fall. "Very light" means that the scattered drops do not completely wet a surface. "Light" means it is greater than a trace and up to 2.5 mm an hour. "Moderate" means the rate of fall is between 2.6 mm to 7.5 mm per hour. "Heavy" means 7 mm per hour or more. rainfall, snowfall, and precipitationRain, drizzle, freezing rain, freezing drizzle and hail are usually measured using the standard Canadian rain gauge, a cylindrical container 40 cm high and 11.3 cm in diameter. The precipitation is funneled into a plastic graduate that serves as the measuring device. Snowfall is the measured depth of newly fallen snow, measured using a snow ruler. Measurements are made at several points which appear representative of the immediate area, and then averaged. "Precipitation" in Canadian Climate Normals tables is the water equivalent of all types of precipitation. At most ordinary stations the water equivalent of snowfall is computed by dividing the measured amount by ten. At principal stations it is usually determined by melting the snow that falls into Nipher gauges. These are precipitation gauges designed to minimize turbulence around the orifice, and are high enough above the ground to prevent most blowing snow from entering. The amount of snow determined by this method normally provides a more accurate estimate of precipitation than using the "ten-to-one" rule. Even at ordinary climate stations the normal precipitation values will not always be equal to rainfall plus one tenth of the snowfall. Missing observations is one cause of such discrepancies. Precipitation measurements are usually made four times daily at principal stations. At ordinary sites they are usually made once or twice per day. Rainfall, snowfall and precipitation amounts given in the tables represent the average accumulation for a given month or year. relative humidity (%)Relative humidity is the ratio of the actual amount of water vapour present in the air compared to the maximum amount of water vapour that would be present if the air were saturated at a particular temperature. It is usually expressed in percentage.
saturation pointThe point when the water vapour in the atmosphere is at its maximum level for the existing temperature. smoke or hazeA suspension in the air of small particles produced by combustion. Viewed through smoke, the sun appears very red at sunrise and sunset. When high in the sky, smoke is tinged with orange. Smoke from nearby cities may be brown, dark gray or black. Smoke in extensive layers originating from forest fires give the sky a greenish-yellow hue. Evenly distributed smoke from distant sources is generally light gray or blue. In large quantities, smoke may be distinguished by its smell. Plumes of smoke of local origin are not reported as an atmospheric phenomenon. snowFrozen precipitation in the form of white or translucent ice crystals in complex branched hexagonal form. It most often falls from stratiform clouds, but can fall as snow showers from cumuliform ones. At temperatures > than -5° C, the crystals generally cluster to form snowflakes. snow depthSnow depth is the depth of accumulated snow on the ground, measured at several points that appear representative of the immediate area and then averaged. snow grainsFrozen precipitation in the form of very small, white opaque grains of ice. The solid equivalent of drizzle. Their diameter is generally < 1 mm. When grains hit hard ground, they do not bounce or shatter. They usually fall in very small quantities, mostly from Status clouds or fog and never in the form of a shower. snow pelletsFrozen precipitation of particles of either spherical or conical ice; their diameter is about 2 to 5 mm. They are brittle, easily crushed, and unlike hail, when they fall on hard ground, they bounce and often break up. Snow pellets always occur in showers and are often accompanied by snow flacks or raindrops when the surface temperature is around 0° C. snow on the ground (cm)The depth of snow in centimetres (cm) on the ground. The total depth of snow on the ground at the time of the observation is determined in whole centimetres by making a series of measurements and taking the average. snow showersaturation pointFrozen precipitation in the form of snow, characterized by its sudden beginning and ending. snow squallA heavy snow shower accompanied by sudden strong winds. snow surveySnow surveys by designated stations are made at regular intervals during the
winter months to determine the water equivalent (mm) and depth of the snow
pack (cm). solar radiationSolar radiation is the measurement of radiant energy from the sun, on a horizontal surface. There are several standardized components of independent measurements. Each component is assigned a different identifying number referred to as Radiation Fields (RF). The standard metric unit of radiation measurement is the megajoule per square metre (MJ m-2). Components measured and used by MSC: RF1: Global Solar Radiation: the total incoming direct and diffuse short-wave solar radiation received from the the whole dome of the sky on a horizontal surface. RF2: Sky Radiation (Diffuse): the portion of the total incoming short-wave solar radiation received on a horizontal surface that is shielded from the direct rays of the sun by means of a shade ring. RF3: Reflected Solar Radiation: the portion of the total incoming short-wave radiation that has been reflected from the Earth's surface and diffused by the atmospheric layer between the ground and the point of observation onto a horizontal surface. RF4: Net Radiation: the resultant of downward and upward total (solar, terrestrial surface, and atmospheric) radiation received on a horizontal surface soil temperatureSoil temperature measurements provide a climatology of soil thermal characteristics such as the depth of frost penetration into the soil and the duration that the soil remains frozen. It is of interest to hydrologists because it affects surface runoff, infiltration and snowmelt and to agriculturists because it affects seed germination. Measurements of soil temperature are made in accordance with the World Meteorological Organization (WMO) recommendations at the standard depths of 5, 10, 20, 50, 100, 150 and 300 cm. They are measured daily as close as possible to 08:00 LST and again at the shallowest depth at 16:00 LST. speed of maximum gust (km/h)The speed in kilometres/hour (km/h) of the maximum wind gust during the day. The gust is the maximum or peak instantaneous or single reading from the anemometer (the instrument used to observe wind speed) during the day. The duration of a gust typically corresponds to an elapsed time of from 3 to 5 seconds. This value is not reported for a day if the maximum speed does not exceed 30 km/h. Station nameThe station name is the official name of any meteorological station in the Climate National Archive as administered by the Meteorological Service of Canada (MSC). STATION ID, STATION NUMBER, CLIMATE IDAlso referred to as climate ID or station number, the station ID is a 7 digit number assigned by the Meteorological Service of Canada to a site where official weather observations are taken, and serves as a permanent, unique identifier (ID). The first digit of the number indicates the province in which the observing site is located; the second and third digits identify the climatological district within the province. When observations are discontinued at a site, the number is not used for subsequent stations (which may, or may not, differ in name) unless it is judged that the records from the earlier and subsequent stations may be combined for most climatological purposes. Station Pressure (kPa)The atmospheric pressure in kiloPascal (kPa) at the station elevation. Atmospheric pressure is the force per unit area exerted by the atmosphere as a consequence of a mass of air in a vertical column from the elevation of the observing station to the top of the atmosphere. Station statusIndicates whether a station is currently collecting and/or transmitting weather data. An "active" or "open" station is considered operational and is expected to provide ongoing information. An "inactive" or "closed" station no longer collects or transmits data. Surface Weather ObservationA surface weather observation is an evaluation of meteorological elements, visually and/or by measurement at a specified location on the earth's surface, usually a weather observing station. Synoptic ObservationsSynoptic observations consist of sky condition, wind speed and direction; visibility, weather and obstructions to vision, atmospheric pressure, temperature, dew point, precipitation amount, special phenomena and maximum and minimum temperature. Observations are taken at specified times (usually at 0000 UTC, 0600 UTC, 1200 UTC and 1800 UTC) simultaneously around the globe and collectively give a comprehensive "synoptic" picture of weather conditions.
TC IdA 3-digit number assigned by Transport Canada in cooperation with NavCan. The TC id identifies meteorological reports from airport observing sites transmitted in real time in aviation formats. Only such locations have a TC Id. temperature (°C)The temperature of the air in degrees Celsius (C). The measure of molecular motion or the degree of heat of a substance. It is measured on an arbitrary scale from absolute zero, where the molecules theoretically stop moving. It is also the degree of hotness or coldness. In surface observations, it refers primarily to the free air or ambient temperature close to the surface of the earth. At most climatological stations the maximum temperature is the highest recorded in a 24-hour period ending in the morning of the next day. The minimum values are for a period of the same length, beginning in the evening of the previous day. Mean temperature is the average of the two. At most principal stations the maximum and minimum temperatures are for a day beginning at 0600 Greenwich (or Universal) Mean Time, which is within a few hours of midnight local standard time in Canada. thunderstormA thunderstorm is a local storm produced by a cumulonimbus cloud. It is an event of relatively short duration and is always accompanied by lightening and thunder and lightning, usually with strong gusts of wind, heavy rain and sometimes hail. Officially, a thunderstorm is reported when: 1.) thunder is heard with the past 15 minutes thunderThe sound emitted by rapidly expanding gases along the channel of a lightning discharge. Most of lightning's electrical discharge is used to heat atmospheric gases around the visible channel. Temperatures can rise to over 10,000 °C in microseconds, resulting in a violent pressure wave, composed of compression and rarefaction. The rumble of thunder is created as one's ear catches other parts of the discharge, the part of the lightning flash nearest registering first, then the parts further away. total precipitation (mm)The sum of the total rainfall and the water equivalent of the total snowfall observed during the day. The point when the water vapour in the atmosphere is at its maximum level for the existing temperature. total rain (mm)The total rainfall, or amount of all liquid precipitation such as rain, drizzle, freezing rain, and hail, observed during the day. total snow (cm)The total snowfall, or amount of frozen (solid) precipitation in cm such as snow and ice pellets, observed during the day. traceAn unmeasurable or insignificant quantity. A precipitation amount of less than 0.02 mm.
Universal Time Coordinates (UTC)UTC is the local time on the zero meridian (0°) which goes through the old observatory in Greenwich, London, UK. The World Meteorological Organization (WMO) has adopted the UTC as the standard time for reporting all meteorological data internationally. Times in UTC sometimes get the suffix Z, i.e. 16Z. From the mnemonic "Zulu", as used in international marine communications standards. Upper AirReadings of pressure (kPa), altitude (m), air temperature (C), relative humidity (%), wind speed (m/s), and wind direction (degrees) for standard pressure surfaces at 00 and 12 UTC at..
vapour pressureThe pressure exerted by the molecules of a given vapor. In meteorology, it is considered as the part of total atmospheric pressure due to the water vapor content. It is independent of other gases or vapours. visibility (km)Visibility in kilometers (km) is the distance at which objects of suitable size can be seen and identified. Precipitation, fog, haze or other obstructions such as blowing snow or dust can reduce atmospheric visibility.
weatherThe state of the atmosphere at a specific time. It is the short term or instantaneous variations of the atmosphere, as opposed to the long term, or climatic, changes. Weather Observing StationA weather observing station is any site from which official weather observations are made. It is normally equipped with instruments for measuring meteorological elements. wet bulb temperatureThe wet bulb temperature differs from the dry bulb temperature by an amount dependent on the moisture content of the air and is normally the same as or lower than the dry bulb temperature. windWind is defined as air in motion. It represents the horizontal flow of air
at a height of 10 meters. Wind information includes direction, speed and character.
Wind in the first ten's of metres above the ground tends to increase in speed
and veer with height. Wind Chill Wind chill is an index to indicate how cold the weather feels to the average
person. It is derived by combining temperature and wind velocity values into
one number to reflect the perceived temperature. The standard Wind Chill formula for Environment Canada is: W = 13.12 + 0.6215 + 0.3965 x Tair - V10m + 0.3965 x Tair - V10m where wind directionThe direction from which the wind is blowing with respect to true or geographic north (360 degrees on the compass). For example, an easterly wind is blowing from the east, not toward the east. It represents the average direction during the two minute period ending at the time of observation and is expressed to the nearest 10 degrees, or to one of the 16 points of the compass (N, NE, WNW, etc.). Expressed in ten's of degrees, 9 means 90 degrees true r an east wind, and 36 means 360 degrees true or a wind blowing from the geographic North Pole. A value of zero (0) denotes a calm wind. wind speed (km/h)The speed of motion of air in kilometres per hour (km/h) usually observed at 10 metres above the g round. It represents the average speed during the two-minute period ending at the time of observation. In observing, it is measured in nautical miles per hour or kilometers per hour. Conversion factors: 1 nautical mile = 1852 metres or 1.852 km World Meteorological Organization (WMO)Since weather systems and climatic conditions extend beyond international boundaries, it is necessary to exchange weather information freely throughout the world. This requires coordination and standardization of practices and procedures for efficient exchange of weather transmissions. To promote these services and to further the application of meteorology to aviation, shipping, agriculture and other human activities, the World Meteorological Organization was established by the United Nations in 1951. Its weather reporting codes are called International Codes. WMO IdUpper AirA 5-digit number permanently assigned to Canadian Stations by the World Meteorological Organization to identify the station internationally. The WMO ID is an international identifier assigned by the Meteorological Service of Canada to standards of the World Meteorological Organization for stations that transmit observations in international meteorological formats in real time. WMO Standards for "CLIMATE NORMALS""Climate averages", "climate means" or "climate normals" are all interchangeable terms. They refer to arithmetic calculations based on observed climate values for a given location over a specified time period and are used to describe the climatic characteristics of that location. Real-time values, such as daily temperature, are compared to the "climate normal" to determine how unusual or how great the departure from "average" they are. There are many ways to calculate "climate normals"; the most useful ones adhere to accepted standards. The WMO considers thirty years long enough to eliminate year-to-year variations. Thus the WMO climatological standard period for normals calculations are "averages of climatological data computed for consecutive periods of 30 years as follows: 1 January 1901 to 31 December 1930, 1 January 1931 to 31 December 1960, etc." and should be updated every decade. In addition, the WMO established that normals should be arithmetic means calculated for each month of the year from daily data. To qualify, temperature data, soil temperatures and evaporation must fit the following rule: "If more than 3 consecutive daily values are missing or more than 5 daily values in total in a given month are missing, the monthly mean should not be computed and the year-month mean should be considered missing." This is referred to as the "3/5" rule. For total precipitation, degree-days, and "days with" calculations, no missing days are allowed. Once the months that qualify are determined, a similar "3/5" rule is also applied to the number of monthly average or total values in the thirty-year period. For instance, to meet this WMO standard, the "normal" value of a monthly element, such as the normal rainfall amount for May, can have no more than 3 consecutive, or 5 in total, missing rainfall values in any month of May between 1971 to 2000. For the purposes of the Canadian Climate Normals, calculated for 1971 to 2000, locations or climate stations, which meet to these WMO standards, are referred to as Class "A".
 Created : 2002-06-21
Modified : 2004-03-03
Reviewed : 2004-03-03
Url of this page : http://www.climate.weatheroffice.ec.gc.ca/prods_servs/glossary_e.html
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