Glossary

Brought to you by the Alberta Climate Information Service (ACIS)


Average Dew Point Temperature (C): The dew point or dewpoint of a given parcel of air is the temperature to which the parcel must be cooled, at constant barometric pressure, for the water vapor component to condense into water, called dew.

Average Relative Humidity (%): A dimensionless ratio, expressed in percent, of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. Since the latter amount is dependent on temperature, relative humidity is a function of both moisture content and temperature.

Average Temperature (C): The average temperature for a day computed by averaging either the hourly readings or, the maximum and minimum temperatures.

  T = (Tmax + Tmin) / 2

Average Wind Direction (degrees): The true direction from which the wind is blowing at a given location (i.e., wind blowing from the north to the south is a north wind). It is measured in degrees from 1 degree clockwise through 360 degrees. North is 360 degrees.

Average Wind Direction Deviation (degrees): The average departure from the average wind direction, measured in degrees. A small number indicates a constant wind direction; a large number indicates a shift in the wind direction.

Average Wind Speed @ 10m (km/h): The rate at which air is moving horizontally past a given point, measured in kilometers per hour at a height of 10 metres above the ground.

Average Wind Speed @ 2m (km/h): The rate at which air is moving horizontally past a given point, measured in kilometers per hour at a height of 2 metres above the ground.

Climate ID: A unique identifier assigned by the Meteorological Service of Canada for each location having archived observations.

Corn Heat Unit (CHU): There is a wide selection of hybrids and varieties for most crops. Most of the warm-season crops have a wide range of maturities. Corn Heat Units (CHU) provide an indexing system to assist farmers to select the most suitable hybrids and varieties for their area. The corn heat unit ratings are based on the total accumulated corn heat units from May 15 each year until the first time in fall, the minimum temperature reaches -2°C.

   CHU = (1.8((Tmin - 4.4) + 3.3(Tmax-10) - 0.084(Tmax - 10)2))/2.2
   Where:
   Tmax = Daily maximum temperature (°C)
   Tmin = Daily minimum temperature (°C)

Crop Moisture Use: The amount of moisture that a crop uses for growth, expressed in millimeters.

Date of First Fall Frost: First day in fall when the daily minimum temperature is below zero degrees Celsius.

Date of Last Spring Frost: Last day in spring when the daily minimum temperature is below zero degrees Celsius.

Elevation: The measure of height with respect to a point on the earth's surface above mean sea level, expressed in metres.

Evapotranspiration: The loss of water from the earth's surface through the combined processes of evaporation (from the soil and plant surfaces) and plant transpiration (from the soil through the roots and stem, and out through the leaves to the air).

Frost Free Day: A day where the temperature does not fall below zero degrees Celsius.

Growing Degree Day (GDD): Growing degree days, or GDDs, are used to estimate the growth and development of plants during the growing season. GDD is calculated by subtracting the base temperature from the mean temperature. If the daily GDD calculates to a negative number it is made equal to zero. Each daily GDD is then added up (accumulated) over the growing season.

The GDD equation is as follows:

GDDDaily = ((Tmax + Tmin) / 2) - Tbase

where:

  Tmax = the daily maximum air temperature
  Tmin = the daily minimum air temperature
  Tbase = the GDD base temperature for the organism being monitored

Growing Degree Days5: It has been determined experimentally that the base temperature or (Tbase) for field crops is 5°C. GDD5 refers to 5°C being used as the base temperature in the GDD equation.

GDD5 = ((Tmax + Tmin)) / 2) - 5

Initial Setup Date: The date that the weather station first became operational with near real time data transmissions.

IRRI-Cast: The IRRI-Cast report provides up to date crop water use information for specific crops in the selected station growing area. The IRRI-Cast also provides an expected crop water use forecast for the next five days.

Killing Frost: If a frost period is sufficiently severe to end the growing season (or delay its beginning), it is commonly referred to as a killing frost. This usually requires a temperature below -2°C for a sufficient duration.

Latitude: The location north or south in reference to the equator, which is designated at zero (0) degrees. They form parallel lines that circle the globe both north and south of the equator. The poles are at 90° North and South latitude.

Longitude: The 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.

Long Term Average: A value derived by averaging values over a number of years.

Maximum Relative Humidity (%): The highest humidity during a 24-hour period.

Mean Relative Humidity (%): The average of the highest and lowest humidity during a 24-hour period.

Maximum Temperature (C): The highest temperature during a 24-hour period, expressed in degrees Celsius.

Mean Temperature (C): The average of the highest and lowest temperatures during a 24-hour period, expressed in degrees Celsius.

Minimum Relative Humidity (%): The lowest humidity during a 24-hour period.

Minimum Temperature (C): The lowest temperature during a 24-hour period, expressed in degrees Celsius.

Near Real Time: The most recent climate data reported from an Ag-Meteorological Station. These hourly readings include: precipitation, temperature, humidity, wind direction and speed. This data has not gone through the final stages of error checking and quality control and is displayed as preliminary data.

Official Station Name: The name assigned to the met station.

Physiological Day or P-Days: P-days is an indexing system, widely used in potatoes for determining stage of development and initiation of disease. With the P-Day approach, the minimum temperature for potato growth and development is 7°C, while the most rapid growth and development takes place at 21°C. The growth rate decreases with the increase in temperature and finally stops at 30°C. From this information, heat units for potatoes, called "P-Days" can be calculated.

Precipitation (mm): All forms of water that fall from the sky and reach the ground. The amount of fall is expressed in millimetres of liquid water depth of the substance that has fallen at a given point over a specified time period.

Rainfall: Liquid precipitation that is in the form of water droplets larger than 0.5mm. It is the amount that is measured by a rain gauge. It is expressed in millimeters.

Range: A column of townships in the north-south direction is called a range. Townships lie in ranges numbered westward from each Initial Meridian, starting with range one adjoining the west side of each such meridian. There are thirty ranges between the Fourth and Fifth meridians along the 49th parallel, but due to convergence of the meridians, this reduces to only about twenty-three ranges along the north boundary of Alberta.

Reference Evapotranspiration (mm): Evapotranspiration rate from a uniform surface of dense, healthy, actively growing alfalfa or grass having specified height (50 cm for alfalfa and 12 cm for grass), not short of water.

Solar Radiation (W/m2/day): The amount of radiant energy received at the earth's surface, available at a vegetation or soil surface for evaporating water, heating the air or heating a surface. It is expressed in watts per square metre per day.

Temperature of First Fall Frost: The minimum temperature on the first day in fall when the daily minimum temperature is below zero degrees Celsius, expressed in degrees Celsius.

Temperature of Last Spring Frost:The minimum temperature on the last day in spring when the daily minimum temperature is below zero degrees Celsius, expressed in degrees Celsius.

Township: A township is a square tract of land about six miles (9.7 kilometres) on a side, containing thirty-six sections. Townships are numbered northward, starting from township one at the 49th parallel and increasing to township 126 at the 60th parallel.

Transport Canada ID: The TC ID is the identifier assigned by Transport Canada to identify meteorological reports from airport observing sites transmitted in real time in aviation formats. Only such locations have a TC ID.

Wind - Average Hourly: The rate at which air is moving horizontally past a given point, measured in kilometers per hour.

Wind Run @ 10m (km/day): The rate at which air is moving horizontally past a given point, measured in kilometers per day at a height of 10 metres above the ground. It is the summation of 24 average hourly wind speed, starting at 12 a.m. and ending at 11:59 p.m.

Wind Run @ 2m (km/day): The rate at which air is moving horizontally past a given point, measured in kilometers per day at a height of 2 metres above the ground. It is the summation of 24 average hourly wind speed, starting at 12 a.m. and ending at 11:59 p.m.

World Meteorology Organization ID: 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.