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Technical documentation: Historical Hourly Climate Station Data

This is the technical documentation for the Hourly Data. The documentation provides a general overview of the dataset, a description of how the dataset was created, potential applications and any limitations of the dataset. For a general overview of climate information concepts, explore Climate information basics.

Overview

Canadian hourly climate data are available for public access from the ECCC/MSC's National Climate Archive. These are surface weather stations that produce hourly meteorological observations, taken each hour of the day. Only a subset of the total stations found on Environment and Climate Change Canada's Historical Climate Data Page is shown due to size limitations. The criteria for station selection are listed as below.

The priorities for inclusion are as follows:

Main Characteristics

Variables

Spatial resolution and geographical coverage

Time period

Temporal  resolution

Data Descriptions

Temperature (°C)

The temperature of the air in degrees Celsius (°C). At most principal stations the maximum and minimum temperatures are for a day beginning at 0601Z - Greenwich Mean Time, also known as UTC or Universal Time Coordinates, which is within a few hours of midnight local standard time in Canada.

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.

Dew Point Temperature (°C)

The dew point temperature in degrees Celsius (°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.

Relative Humidity (%)

Relative humidity in percent (%) is the ratio of the quantity of water vapour the air contains compared to the maximum amount it can hold at that particular temperature.

Precipitation

Any form 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 are classified as: 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 expressed to the nearest 0.2 mm. Less than 0.2 mm is called a "Trace". For climate stations operating on a 24 hour basis, total precipitation measurements end at 0600Z of the following day.

Wind Direction (10's deg/tens of degrees)

The direction (true or geographic, not magnetic) from which the wind blows. It represents the average direction during the two-minute period ending at the time of observation. Expressed in tens 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. 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 ground. It represents the average speed during the one-, two- or ten-minute period ending at the time of observation. In observing, it is measured in nautical miles per hour or kilometres per hour.

Conversion factors:1 nautical mile = 1852 metres or 1.852 km

Therefore 1 knot = 1.852 km/h

And 1 km/h = 0.54 knot.

Visibility (km)

Visibility in kilometres (km) is the distance at which objects of suitable size can be seen and identified. Atmospheric visibility can be reduced by precipitation, fog, haze, or other obstructions to visibility such as blowing snow or dust.

Station Pressure (kPa)

The atmospheric pressure in kilopascals (kPa) at the station elevation. Atmospheric pressure is the pressure exerted by the weight of air above a given point, sometimes expressed in millibars (mb) or inches of mercury (Hg). The internationally recognized unit for measuring atmospheric pressure is the kilopascal (kPa).

Humidex

Humidex 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. For example, a humidex of 40 means that the sensation of heat when the temperature is 30 degrees and the air is humid, feels more or less the same as when the temperature is 40 degrees and the air is dry. Hourly Humidex values are only displayed when the air temperature is 20C or greater and the humidex value is at least 1 degree greater than the air temperature.

The standard Humidex formula used by Environment and Climate Change Canada is:

Humidex = (air temperature) + h

Where
h = (0.5555)*(e – 10.0);
e = vapour pressure in hPa (mbar), given by:
e = 6.11 * exp[5417.7530 * ( (1/273.15) – (1/dewpoint) ) ]
exp = 2.71828

Dewpoint is expressed in kelvins(K) (temperature in K = temperature in °C + 273.15) and 5417.7530 is a rounded constant based on the molecular weight of water, latent heat of evaporation, and the universal gas constant.

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.
For example, if the outside temperature is -10 °C and the wind chill is -20, it means that your face will feel more or less as cold as it would on a calm day when the temperature is -20 °C.

There are two Wind Chill formulas used by Environment and Climate Change Canada. The first equation is used when the temperature of the air is ≤ 0 °C and the reported wind speed is ≥ 5 km/h. The second equation is used when the temperature of the air is ≤ 0 °C and the reported wind speed is > 0 km/h but < 5 km/h.

The standard Wind Chill formula for Environment and Climate Change Canada is:

  1. W = 13.12 + 0.6215 × Tair – 11.37 × V10m0.16 + 0.3965 x Tair × V10m0.16
  2. W = Tair + [(-1.59+0.1345 × Tair)/5] × V10m

Where:
W is the wind chill index, based on the Celsius temperature scale
Tair is the air temperature in degrees Celsius (°C), and
V10m is the wind speed at 10 metres (standard anemometer height), in kilometres per hour (km/h).

Weather

Observations of atmospheric phenomenon including the occurrence of weather and obstructions to vision.

Precipitation types are observed in three intensities: light, moderate and heavy. If the precipitation is listed in the WEATHER column without a modifier, then the intensity is light. Otherwise, it will appear with a modifier of moderate or heavy.

When no weather or obstructions to visibility occur, sky conditions are provided reflecting the observation of total cloud amount. The following terms are used based on the amount (in tenths) of cloud covering the dome of the sky:

User Limitation

Methods

Contact Information

Climate Services Support Desk
ccsc-cccs@ec.gc.ca
833-517-0376

Reference

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