Glossary of important frequently used terms
Help - Canadian station weather data and extreme winter events

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Extreme
  • Means something different depending on whether referring to extreme weather or extreme index

  • Extreme weather means for temperatures the warmest (extreme high) and coldest (extreme low) days while for precipitation it means the days with the greatest amounts (extreme high) or even days with a measureable amount (any). The exact values that determine the extreme weather variable thresholds vary from station to station, but the definitions to determine them are consistent. For temperature the extreme high and low are respectively the warmest and coldest 1/15th of the observations, and for precipitation the extreme high amounts are those that make up the top 20% of the days with recorded measureable amounts.

  • Extreme index means days when the teleconnection pattern is most pronounced. For the daily-defined NAM and PNA those are essentially the days the daily index value is greater than +1 (extreme positive) or less than -1 (extreme negative), while for the CTI it refers to moderate-to-strong El Niño winters (extreme positive) or moderate-to-strong La Niña winters (extreme negative)


    • Index
  • Any of the time series of the teleconnections considered here
  • See: NAM  |  PNA  |  CTI


    • Ratio
  • This refers to the extreme weather event days at a station under the two opposite extremes (high and low) of an index. The ratio is the quotient of the number of extreme high index days with that type of extreme weather divided by the number of extreme low index days with that type of extreme weather or the number of extreme low index days with that type of extreme weather divided by the number of extreme high index days with that type of extreme weather, whichever gives a number >=1. If there were more extreme high index days the ratio is color-coded red, and if there were more extreme low index days the ratio is color-coded blue.


    • Station
  • Any data record for a particular location. It has a name, and the general location is usually obvious, but the name may be difficult to interpret exactly. An "A" at the end generally means "Airport". A number followed by a cardinal direction (e.g., 3NNE) means the station is that distance in that direction from a location in the name.


    • Statistical significance
  • A ratio result may be said to be "statistically significant" if it passed the test for statistical significance used here. This test is not perfect, especially the less complete a data record is, but it still gives a good idea for many stations whether a given ratio is different from what may occur randomly if there was no real correlation between a weather variable and an index. "Significant" ratios are noted on station pages with an asterisk (*) following the value, and ratio maps are made in some cases showing only the "significant" stations.


    • Weather variable
  • Any one of the types of daily weather data examined here
  • See: TMAX  |  TMIN  |  TEMP  |  PRCP  |  SNOW  |  RAIN