Technical documentation: Daily Climate Records (LTCE)

This is the technical documentation for the Daily Climate Records database, also known as the Long Term Climate Extremes database (LTCE).

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 list of Frequently Asked Questions, visit the FAQ page. For a general overview of climate information concepts, explore Climate information basics.

Overview

The Daily Climate Records database, also known as Long Term Climate Extremes (LTCE), was built to deal with fragmented climate information due to station changes (opening, closing, relocation etc.) over time.

For close to 750 urban locations in Canada, “virtual” climate stations were created by joining together (threading) the climate data from stations nearby to make long-term records. Each long-term record contains the extremes (record values) of daily maximum/minimum temperatures, total precipitation and snowfall for each day of the year.

Many of the longest data sets of extremes date as far back as the 1800s. For example, the dataset identifies the highest temperature or the greatest snowfall on record for each day of the year for the chosen urban area.

Variables and formats

The Daily Climate Records provide daily values for three different variables:

• The daily extremes of record for temperature for each day of the year. Elements include high maximum, low maximum, high minimum and low minimum.
• The daily extremes of record for precipitation for each day of the year. Elements include greatest precipitation.
• The daily extremes of record for snowfall for each day of the year. Elements include greatest snowfall.

Note: all variables represent surface conditions (typically ~1.5 meter above the ground) at the station’s location.

Methods

Methods - Observations

You can use the following guidelines to find out the times of observation and the endpoint of the climatological day for temperature and precipitation elements:

• For climate stations operating on a 24 hour basis, since July 1, 1961, the climatological day for temperature and precipitation ends at 0600Z of the next day.
• From June 1, 1957 to June 30, 1961, the climatological day for precipitation and maximum temperature ended at 1200Z of the next day. The climatological day for minimum temperatures ended at 0000Z of the next day.
• Before June 1, 1957, the climatological day for precipitation and maximum temperature ended at 1230Z of the next day. The climatological day for minimum temperatures ended at 0030Z of the next day.

At locations with no hourly observations, observation times are generally morning and evening local time. In general, the climatological day for precipitation and maximum temperature ends at the morning observation of the next day. The climatological day for minimum temperatures ends at the afternoon observation of the current day. For sites reporting only once per day, the calendar day rather than climatological day applies.

Methods - Threading

Each of the City Page locations of weather.gc.ca has a Virtual climate station.  A virtual climate station is the result of threading (joining) together climate data from nearby current and historical stations to build a long-term dataset. All available data within a 20 km radius of each urban center was searched and catalogued.

The starting point is a representative, currently active station in the area of the urban center. These data were followed backward in time until it was no longer available or until it was replaced by a higher quality dataset from the same station.

When we reached the earliest or end point of a thread fragment, we chose an alternate from the catalog, keeping in mind data quality, proximity to the prior station and any gaps in data length. We  repeated this process until the thread extended back in time as far as possible. Finally, we used local expertise to subjectively fine tune the threads.

The radius around an urban centre to collect candidate data for creating threads was set to 20km. Consultation sessions were used to decide the radius based on consensus. Because it was an arbitrary value, some latitude was permitted to include data which was close to the 20 km cut-off during the subjective review stage.

In a small percentage of cases where there is no currently active climate station within 20 km of the urban center, an alternate station may have been chosen from representative stations at a maximum radius of 35 km.

Station list

The lists of LTCE virtual climate stations for each variable are available below as CSVs.

• Download a list of detailed information for each LTCE virtual climate station with temperature record type only
• Download a list of detailed information for each LTCE virtual climate station with precipitation record type only
• Download a list of detailed information for each LTCE virtual climate station with snowfall record type only

To get station information for all segments of the LTCE virtual climate stations, please use:

• Download a list of detailed information for each LTCE virtual climate station

Application

Climate station relocations, closures, openings etc. have led to a fragmentation of climate information. Referring to a long time series of data for a location and computing extremes is difficult and time-consuming. In order to identify and calculate daily extremes of record for temperature, precipitation and snowfall, the Meteorological Service of Canada has threaded or put together data from closely related stations to create a long time series of data for 750 locations in Canada.

These data should not be used to answer questions about climate change. For climate change or trend detection, the data would have to be adjusted to remove such artifacts as discontinuities and non-climate trends.

Please refer to the Adjusted and homogenized Canadian climate data for climate change purposes.

Users are urged to assess whether the LTCE datasets are suitable for their application.

Limitations

Note that there may be missing values in the LTCE dataset, which may vary by variable, station and time. There is a small percentage of virtual stations with gaps in the period of record because of no data or no operating station being available for the period. These gaps have been minimized and most are less than 20 years. 

Constructing a thread in locations, and at times where there are multiple alternates will necessarily lead to exclusion of some data. The data to be included in a thread was reviewed by regional experts and sometimes subjective choices were made based on local knowledge, perceived quality and completeness of data.

There will be more unused data in areas where station density is greatest. Unused data are available in the National Climate Archives. You can find the data online at Environment and Climate Change Canada’s Historical Climate Data Page.

All data that is brought into the Environment Canada Climate Data Archive is initially screened. Data in the archive has had a variable amount of quality review and not all data is quality controlled. For instance, some Partner stations provide data to the National Climate Archives which does not undergo Archive review processes. All data is subject to revision. When changes are made, the data are automatically passed to the LTCE database upon the next refresh (twice daily).

Other Considerations

Note that ongoing station changes, new stations and closures will result in future revisions of the LTCE thread composition and dataset.

Use Limitation

Open Government License

Contact Information

Climate Services Support Desk
info.cccs-ccsc@canada.ca
1-833-517-0376

Reference

MANOBS Manual of Surface Weather Observations

Technical Documentation - Digital Archive of Canadian Climatological Data

LTCE Frequently Asked Questions