About Canadian weather radar

Brief description of the radar layer

The radar layer displayed on our platform is based on a mosaic calculated over the North American domain with a horizontal spatial resolution of 1 km. This mosaic therefore includes all the Canadian and American radars available in the network and which can reach a maximum of 180 contributing radars. Figure 1 shows the extent of the area covered by the mosaic as well as the density of contributing radars (white circles). The coverage is marked by numerous areas of overlap between the radars, which is very useful in the event of scheduled or sudden failures of certain radars. This composite is available every 10 minutes. This frequency will increase from 10 minutes to 6 minutes when all C-Band radars will have been replaced by the new S-Band radars (more information about the project is available here: Canadian Network Modernization of meteorological radars).

To better represent precipitation over the different seasons, this mosaic renders in mm/h to represent rain and in cm/h to represent snow. For the two precipitation types (rain and snow), we use two different mathematical relationships to convert the reflectivity by rainfall rates (mm/h rain cm/h for snow). Note also that these mosaics are available in a palette of 8 and 14 colors (intensity levels of radar echoes). Figures 2 and 3 illustrate two examples; one representing the precipitation rate of rain and the second representing the precipitation rate of snow.

This is a hybrid mosaic composed of different estimation precipitation products. Below are the technical description of each product used and the context of their use:

1. PRECIP-ET Product: PRECIP-ET is a two-dimensional product used only for C-Band radars (which are in the process of being replaced with new S-Band radars). It takes into account a quality control algorithm (QC) to better identify the problems and apply the appropriate fixes. For example, Doppler filters can reject moderate ground echoes in some places, bearing the risk that weak weather echoes would go undetected. In such case, PRECIP-ET can indicate the zone where data is missing. Note that the PRECIP-ET is calculated from the lowest radar sweep angle to better represent precipitation near the ground surface (0.4 degree for most radars). PRECIP-ET renders in mm/h for rain and cm/h for snow. This product is calculated with a maximum coverage range of 240 km. A detailed description of it is available here: PRECIP-ET.
2. DPQPE product: DPQPE stands for: Dual-Pol Quantitative Precipitation Estimation. The DPQPE product is available only for S-Band radars. It is a two-dimensional representation of the precipitation rate estimated by the lowest sweep of the radar (elevation angle of 0.4 degrees for the majority of S-Band radars). Thus, the precipitation rate is estimated as close to the earth's surface as possible. The DPQPE product is based, among other things, on a series of polarimetric processing steps (quality control) to eliminate non-meteorological artifacts from the raw data (volumetric scans). It renders in mm/h for rain and cm/h for snow. This product is calculated with a maximum coverage range of 240 km.
3. US NEXRAD product: For the US Nexrad radars, ECCC uses the most similar product from the US Meteorological Service (NOAA). This product displays radar reflectivity converted into precipitation rates, using the same formulas as the Canadian radars. NOAA performs some quality control on its products; ECCC does not perform additional quality control at this time. The spatial resolution and maximum ranges of Nexrad data differ from those of Canadian radars. This product is calculated with a maximum coverage range of 460 km.

Impact of the new S-band radar on the quality of the mosaic

In 2017, ECCC launched the seven-year Canadian Weather Radar Replacement Program (PRRMC) project to replace MSC's current network of aging and obsolete weather radars with a new system of modern dual-polarized radars. This project will allow ECCC to continue to provide Canadians with the weather information they need to make informed decisions about their health, safety and protection. The result of this project will be a modern, affordable and sustainable network of reliable weather radars covering a greater area of Canada with increased range capabilities and the addition of a new radar station in the Fort McMurray region of Alberta. You can follow the installation status of the new radars here: RADAR replacement schedule.

The table below summarizes the main differences between the new S-band radars and the aging C-band radars:

Double polarization and improvement of product quality

One of the main new features of the new S-band radars is the use of dual polarization (polarimetry) technology. The basic premise behind radar weather is that, in addition to know estimate reflectivity, it determines hydrometeor shapes (measurements of the microphysical properties of hydrometeors). This is possible thanks to the dual polarization, which allows the radar to measure both the vertical and horizontal aspects of the targets. By measuring the returns of these two polarizations, the shape and the effects of the different shapes of hydrometeors can be estimated.

From a technical point of view, the added value of polarimetric radars compared to single polarization radars resides mainly in the comparison of the additional information coming from the vertical polarization to the one derived from the horizontal polarization. This information thus makes it possible to distinguish the different types of precipitation, and greatly improves the observations, allowing to produce better quality forecasts and to issue warnings to the public in the case of extreme weather conditions.

The benefits of such technology can be summed up in the following points:

• Significantly improve the precision of quantitative estimates of precipitation;
• Identify with precision the different types of precipitation and improve the forecasts of liquid or equivalent solid water (differentiate rain, snow, etc.) - better treatment of the bright band;
• Simplify (or even eliminate some of them) the quality control algorithms used by forecasters to target meteorological signals in single polarization radar;
• Increase confidence in radar data, which is the basis for preparing warnings in the event of extreme weather conditions;
• Provide relevant and critical information for estimating precipitation, which helps predict flooding and flood warnings caused by rivers;
• Provide information useful to help municipal authorities in relation to water management;
• Be able to distinguish non-meteorological echoes, which can be dangerous for meteorological aviation such as birds, for example;
• Facilitate and assist the detection of icing conditions in aircraft.

Figures (4) and (5) show the positive impact of dual polarization technology on product quality. This is a comparison between the conventional CAPPI product, which does not use the dual polarization information, and the DPQPE using dual polarization. In both cases (with and without precipitations) for the same radar (Blainville radar covering the greater Montreal area) and for the same date, it demonstrates how the non-meteorological echoes over the southwestern region caused by radial interferences are cleaned when applying the dual polarization information of the DPQPE product.

Accessibility to cleaned DPQPE images

The single S-Band images based on the cleaned DPQPE product using information from the dual polarization are available in real-time on the public site Datamart, accessible here: Single images DPQPE.

Dynamic radar coverage

Radar coverage is provided to dynamically display the zones covered by the radars every 10 minutes, and to provide information on the availability (or not) of the contributing radars as well as on the areas of overlap as shown in Figure 6.