Frequently asked questions about long term climate extremes for Canada
Here we answer the questions we receive most frequently about the Long Term Climate Extremes (LTCE) data.
Questions and Answers
About the Long Term Climate Extremes Project (LTCE)
What is the objective of the Long Term Climate Extremes Project?
Climate records are fragmented because climate stations have been relocated, closed, or new ones have opened. As a result, finding a long time series of data for a location and calculating the extremes is difficult and time-consuming.
In order to find and calculate daily extremes of record for temperature, precipitation and snowfall, The Meteorological Service of Canada threaded (joined) data from closely related stations and put together a long time series of data for about 750 urban areas in Canada. They developed tools to monitor for record-breaking weather (new extremes) and to make it possible to view extremes for any day of the year.
What is a virtual climate station?
A virtual climate station is a set of climate data for a particular geographical area. It comes from threading together pieces of the climate record of nearby current and historical stations to make a long term threaded data set. The length of the time series of virtual stations is often greater than 100 years. A Virtual Climate station will always be named for an “Area” rather than a point, e.g. Winnipeg Area, to indicate that the data are drawn from that area rather than a single precise location.
Exploring the methodology of the LTCE project
What methodology did we use to develop the threads? How did we construct the virtual climate stations?
We searched and catalogued all available data from a 20 km radius of the centre of each urban location found on the “City Pages” on the Environment and Climate Change Canada weather website.
The main active climate station for each area was used as the starting point. These data were followed backward in time until it was no longer available or until it was replaced by a higher quality data set from the same station. When we reached the earliest or end point of a thread fragment, we selected an alternate from the catalog, keeping in mind data quality, nearness to the prior station and any gap in length of time.
We repeated this process until the thread extended as far back in time as possible. Finally, we also used local climatology expertise to subjectively fine-tune the threads.
Can you give an example of how a virtual station was constructed?
Here is an example of how the Virtual Station for the Charlottetown Area’s Daily Maximum Temperature thread was assembled from four component stations:
|Station name||Climate identifier||Start date||End date|
How do I know what data was used to construct a Virtual Station?
The data used to construct a Virtual Station is available in the station metadata file. To get station information for all segments of the LTCE virtual climate stations, please use:
How many virtual climate stations are in the virtual climate station network?
There are approximately 750 Virtual Stations in the network. Virtual long term climate stations were created, providing data were available, for each of the “City Pages” used in the Environment and Climate Change Canada weather website.
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
How climate extremes data is collected
Why did we use a 20 km radius around cities to construct their virtual climate station?
We selected 20 km as an acceptable radius around a city centre based on consensus through consultation sessions. Since it is an arbitrary value, we permitted some latitude to include data which was close to the 20 km cut-off during the subjective review stage. In cases where there was no currently active station within 20 km of the urban center, we used a representative station up to a 35 km radius, if available.
Is the virtual station threading identical for each climate variable?
No, each element may have a different thread composition. That being said, usually the maximum and minimum temperature threads are identical.
What did we do to address gaps in the climate stations record?
We evaluated all available data to make the best thread with the shortest gaps possible. Inevitably there are some gaps, most relatively short (less than 10 years), in the record of some virtual stations.
What happens if new data matches an existing record?
If newer data is identical to an older record, the oldest record is displayed as the official record (value/year) for that date. Tied records are maintained in the LTCE database and available in the Top Five Extremes fields.
Won’t the process of threading climate stations together lead to some data being ignored?
Yes, constructing a thread in locations and at times where there are multiple alternates will lead to excluding some data. Regional climate experts reviewed the data we included in a thread 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 there are the highest number of stations. Unused data stay in the National Climate Archive. You can find the data online at Environment and Climate Change Canada’s Historical Climate Data Page.
How we maintain data accuracy
Do other countries have a similar system station threading system?
Yes, many national meteorological services have a system to join climate records to extend climate history. This system is modeled after the ThreadEx system used in the US.
Has the data been quality controlled?
All data brought in to Environment and Climate Change Canada’s Climate Data Archive, is subjected to initial screening. Data in the archive has had a variable amount of quality review and not all data is quality controlled. For instance, some partner stations send data to the National Climate Archive which does not undergo routine archive review processes.
All data is subject to revision and when changes are made, they are automatically passed to the Long Term Climate Extremes (LTCE) database upon the next refresh (twice daily).
How do these data differ from the climate extremes data available through the Climate Normals and the Almanac Averages and Extremes web pages?
The extremes data tracked by this system come from virtual stations that have been constructed by threading together data from one or more stations. The Climate Normals and Almanac Averages and Extremes sites provide data from unique stations only. There are no joins in the data record. By using the metadata provided for each virtual station and the Almanac Averages and Extremes site, you can derive the same result – but it takes a lot more effort.
How does the database deal with data for February 29th?
February 29 is treated like any other date for the purposes of tabulating daily climate extremes. Since February 29 occurs once every 4 years the population of February 29 data will be smaller than for other dates. Picking the extreme value from a smaller database will affect its magnitude.
This is particularly significant for precipitation elements where the number of precipitation events is less than for temperature (precipitation does not occur every day). In a several instances, some of the Top 5 extremes are non-existent on February 29.
How to obtain and use the LTCE data
Can these data be used to answer questions about climate change?
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 (AHCCD) for climate change purposes.
How do I download data for a station or multiple stations?
Please use the Climate data extraction tool, to download LTCE daily extremes of record for:
- Temperature. Daily elements include high maximum, low maximum, high minimum, and low minimum.
- Precipitation. Daily elements include: greatest precipitation.
- Snowfall. Daily elements include: greatest snowfall.
Is there a Disclaimer that applies to use of these data?
Information presented on this web site is considered public information and may be distributed or copied. An appropriate acknowledgement of Environment and Climate Change Canada as the source is requested.
Environment and Climate Change Canada does not warrant the quality, accuracy, or completeness of any information, data or product from these web pages. It is provided "AS IS" without warranty or condition of any nature.
Environment and Climate Change Canada disclaims all other warranties, either expressed or implied, including but not limited to implied warranties of merchantability and fitness for a particular purpose, with respect to the information, data, product or accompanying materials retrieved from this web site.
I noticed questionable data in the extremes, what should I do?
To report questionable data, please contact us by e-mail at: firstname.lastname@example.org
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