Agroclimatic Atlas of Alberta: Understanding Weather and Climate Data

 
 
Subscribe to our free E-Newsletter, "Agri-News" (formerly RTW This Week)Agri-News
This Week
 
 
 
 Data collection | Mapping climate data | Climate normals and extremes | Using climate information

This document is part of the Agroclimatic Atlas of Alberta.

Data Collection

Weather and climate stations
The maps in this Atlas are based on climate data from over 1200 stations in Alberta and from about 1400 stations bordering Alberta in British Columbia, Saskatchewan, Yukon, Northwest Territories, Nunavut and the United States.

Two types of stations record climate data. Synoptic weather stations typically report near real-time (hourly, 6-hourly, daily) automated weather information using a communication system (satellite or modem). They collect detailed data on air temperature, precipitation amount and intensity, wind speed and direction, humidity and dew point temperature. The information from these stations is used in preparing weather forecasts and in calculating climatic information.

Climate stations typically report less frequently (daily, twice-daily, weekly, monthly) and may be automated or manually operated by volunteers. These stations collect daily temperature and precipitation information, and some used to collect precipitation only.

Figure 5 shows the locations of stations operating during the period from 1971 to 2000. The number of stations in operation changes over time. In 2002, there were about 300 synoptic weather stations and 325 climate stations operating in Alberta. These stations are part of various provincial, federal and independent networks, described below. Each of these networks collects data for specific purposes, depending on the collecting agency's information needs. Not all of the networks described below provided data used in this Atlas.

Environment Canada receives the majority of the data from the federal and provincial networks, performs quality control on the data, and stores the data in the National Climate Archives in Montreal. Data from the United States stations are provided by the U.S. National Climate Data Center.

Alberta government networks
Alberta Agriculture, Food and Rural Development operates two weather station networks: DroughtNet AGDM and Irrigation Network.

Alberta Environment operates stations located mostly in the mountains and foothills. These stations monitor conditions for use in flood river forecasting. Many of the stations are located on rivers, lakes, ridges, headwaters, coulees and creeks. Alberta Environment also has an air quality monitoring network.

Alberta Sustainable Resource Development operates synoptic stations and climate stations mostly in Alberta's forested regions. These stations monitor weather conditions related to forest fire prevention and control.

Alberta Transportation operates a few weather stations in Edmonton and Calgary for monitoring road safety.

Federal government networks in Alberta
Environment Canada operates several networks in Alberta including:

  • the reference climate station network which collects climate data for climate change, global warming, etc.
  • the upper air network which collects data for weather forecasting and air quality.
  • the surface weather network which collects data for public weather forecasting and warnings.
  • the temperature and precipitation network which collects climate data for historical, social and economic reasons including data for special interest groups such as agricultural hail and crop insurance programs. A volunteer network reports temperature and precipitation data either daily or twice daily. Most stations send in their forms once each month, but an increasing number of stations are reporting daily via the Internet or an automated 1-800 phone system.
Transport Canada has privatized the air navigation system as a not-for-profit company known as NavCan. NavCan operates weather stations at many of the airports in Alberta.

Agriculture and Agri-Food Canada operates several automated weather stations at agricultural research stations in Alberta.

Other networks in Alberta
A few weather networks operate independently in Alberta for research or monitoring purposes.

Station names
Some stations have acronyms after the station name. The most common acronyms are:

  • RS – ranger station
  • LO – lookout tower
  • AFS – Alberta Forestry Service (the former name of what is now part of Alberta Sustainable Resource Development)
  • A – airport
  • CDA – Canada Department of Agriculture (the former name of Agriculture and Agri-Food Canada)
  • AGDM – Agricultural Drought Monitoring station.
Instrumentation
Thermometers to measure maximum and minimum air temperature and sensors to determine relative humidity and dew point temperature are placed 1.2 m above the ground in a shelter called a Stevenson screen. The shelter has horizontal, overlapping slats that protect the thermometers from direct sunlight and precipitation, while allowing air to circulate around them.

Rainfall is measured by catching it in a calibrated rain gauge. At most climate stations, a volunteer observer measures rainfall intensity using a standard Canadian rain gauge called a Type B rain gauge. The gauge sits about 40 centimetres (cm) above the ground and has a circular opening 11.3 cm in diameter. The rain is funneled into a clear plastic cylinder which measures the contents to the nearest 0.2 mm.

The majority of climate station observers measure the depth of new snow using a ruler. They estimate the amount of moisture in the snow by assuming a snow density of 100 kilograms per cubic metre. Snow depth is read to the nearest 0.2 cm with less than 0.1 cm is recorded as a trace. The Canadian Nipher Shielded Snow Gauge System is the standard instrument for measuring fresh snowfall water equivalent. It is used at a limited number of stations.

The synoptic weather stations collect wind speed and direction at a height of 10 m above the ground. These stations also measure atmospheric pressure, visibility, cloud cover and type, hours of bright sunshine, solar radiation and, in a few cases, snow depth and evaporation.

Standards
All data used in preparing the maps and tables in this Atlas meet the standards of the World Meteorological Organization (WMO). The WMO publishes the Guide to Meteorological Instruments and Methods of Observations (Reference #6008-2). That guide describes the basic standards of instrument and observing practices required by current international meteorology. It also provides the basis for the preparation of detailed instrument manuals by individual meteorological services for use by their observers. People setting up a weather station should try to follow the WMO standards.

Mapping Climate Data

Each synoptic weather station or climate station provides data for the location of that station, a single point on the surface of the earth. Using such point information to prepare maps of an area requires interpolation, the calculation of the likely values between the points where measurements are taken.

All available quality-controlled data were used in the interpolation procedures for this Atlas. The available data are limited in time and space. A weather or climate station may open, close or move to another location over time. Historically, relatively few synoptic stations operated in the agricultural areas of Alberta during the 1901 to 2000 period. Most synoptic stations were located in the mountain and forested areas and at airports. In addition, many stations represent the local area, not the larger agricultural region.

Climate elements such as temperature and precipitation were calculated for each township of Alberta using an interpolation process. (The Alberta Township Survey System is a grid network with each township being 6 miles by 6 miles in size.) The township climate data were smoothed using computer graphics software. As a result of interpolation and smoothing processes, small differences are introduced when comparing the actual station data and the maps.

The Rocky Mountain area appears white on all the maps. This is because the extreme differences in topography and the limited data available for this area make the interpolation procedure unreliable.

For more details about the interpolation methods used to create the agroclimatic maps in this Atlas, see Interpolation of Climate Station Data.

Climate Normals and Extremes

A long period of weather observations is necessary to understand the climate. Like weather, climate also changes but very gradually. A 30-year period is used in this Atlas to describe the present climate because it is long enough to filter out short-term fluctuations, but is not overridden by any long-term trend in the climate.

Climate normals are the average values for climate characteristics such as temperature, precipitation, wind and humidity. In this Atlas, the climate normals are based on the data for the latest 30-year period, which is 1971 to 2000. The 30-year period is updated only every 10 years because of the massive amount of work involved, and the fact that the average values would not change in a year.

Average values allow quick and easy comparison of the climate of different areas, but they do not describe the inherent variability of climate at any given location. Year-to-year variations result in values that are usually above or below the average. Variability is an expected feature of our climate, which must be remembered when looking at the average values presented in this Atlas.

Climate information is used as a long-term planning tool, for example, in selecting a location for a farm or planning a cropping program. The average is sometimes not adequate for planning because extreme events can disrupt long-term plans. Therefore, this Atlas provides some maps about extremes.

Caution must be used when dealing with data on extreme values because the period of record is very important. The shorter the period of record the less reliable the extreme. If you want to know how much snow was dropped by the worst storm in 100 years, you can not expect a station with only 20 years of records to provide it. The shorter the period of record, the more likely it is that a unique extreme event has been missed.

Extreme Minimum Temperature, Extreme Maximum Temperature, Coldest July Temperature, Warmest January Temperature and Greatest Daily Precipitation maps present extremes for temperature and precipitation. The extreme values on these maps are not averages; they are the interpolated coldest and warmest temperatures and maximum precipitation recorded between 1901 and 2000. This long period of record provides more reliable extreme values than a 30-year period of record. The maps do not represent the entire period of record for all stations because some of the station records started prior to 1901.

Using Climate Information

Farmers are risk managers; their decisions today affect future outcomes. Climate variability is one of the risks they must manage. For instance, when selecting crop types and varieties, they need to assess such aspects as likely fertilizer needs, yield and price potential, and marketability, along with climate.

The climate elements most often used in agricultural decisions are precipitation, sunshine hours, temperature and information derived from temperature, such as degree days and frost dates. Agricultural managers use information on the average conditions as well as the variability in these conditions.

The averages for the climate elements provided in this Atlas show what has happened. This recent history of our climate is our best guide as to the climate conditions that can be expected over the next five to 10 years. Climate elements can also be expressed in terms of the expected ranges or measures of variability. These define what may happen and how often it may occur. By combining knowledge of the agricultural operation with knowledge of what is likely to happen, the agricultural manager can then decide on the acceptable level of risk due to adverse conditions.

Crop producers generally look at the most likely weather conditions rather than the extremes because the key inputs and decisions are made well in advance of achieving results. Severe weather will usually result in reduced yield and/or grade loss, not total crop failure. Crop insurance provides some financial protection from consequences of severe and extreme events.

Most crop varieties common to Alberta are bred to do well over a wide range of climate conditions. In selecting new crop types and varieties, farmers consider climate characteristics like the heat units available, growing season length, frost-free period length and the expected date of fall frost. For example, the yield potential of some crops is closely related to the growing season length or heat units available.

 
 
 
 

Other Documents in the Series

 
  Agroclimatic Atlas of Alberta: Introduction
Agroclimatic Atlas of Alberta: Climate Basics
Agroclimatic Atlas of Alberta: Weather in Alberta
Agroclimatic Atlas of Alberta: Climate of Alberta
Agroclimatic Atlas of Alberta: Understanding Weather and Climate Data - Current Document
Agroclimatic Atlas of Alberta: Agricultural Climate Elements
Agroclimatic Atlas of Alberta: Soil Moisture Conditions in Alberta
Agroclimatic Atlas of Alberta: Soils and Ecoregions in Alberta
Agroclimatic Atlas of Alberta: Maps
Agroclimatic Atlas of Alberta: Interpolation of Climate Station Data
Agroclimatic Atlas of Alberta: Bibliography
Agroclimatic Atlas of Alberta: Appendix
Agroclimatic Atlas of Alberta: Acknowledgements
 
 
 
 
For more information about the content of this document, contact Ralph Wright.
This document is maintained by Deb Sutton.
This information published to the web on September 9, 2003.
Last Reviewed/Revised on September 23, 2008.