Maps of extreme index ratios
Help - Canadian station weather data and extreme winter events

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Click here for help about ratios shown by these maps

For some area, weather variable, and index the ratio maps show the ratios of the occurrences of weather events of interest on the extreme high and low index days. Larger circles indicate larger ratios, i.e., greater magnitude differences between the numbers of weather events on days of extreme high and low index. The circle colors show which index extreme had more weather events associated with it.

• Red circles mean that type of weather event occurred more frequently on extreme high index days than on low
• Blue circles mean that type of weather event occurred more frequently on extreme low index days than on high

Ratio maps are available showing a few different sets of stations, and there are potential positive and negative aspects associated with each station set.

• Only stations whose ratios passed the test for statistical significance (and have at least some specified number of extreme weather events)
• Shows larger ratios without cluttering map with small, possibly meaningless ratios
• However, a data record with a large number of days without observations may result in ratios passing the test of statistical significance without really being meaningful. See the statistical significance help for information on the testing and interpreting the results.

• All stations (having at least some number of extreme events)
• Shows essentially all the results from the available data
• However, ratios close to 1 may have little meaning and be of little interest, and stations with very few extreme weather events may have very large but insignificant ratios of either sign that clutter and may distort the overall picture. See the ratios help for further information and explanation of the ratios.

• Stations having more than or less than some number of extreme events (for precipitation data only)