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Warmest day of the season (99th percentile of daily maximum temperature)

The 'warmest day of the season' is an expression of change in extreme temperature used in UKCP09. It is defined as the 99th percentile of daily maximum temperature on a seasonal basis.

In detail

UKCP09 projects changes in climate extremes. These projections are based on the 99th percentile. Assuming each season is 100 days long, the 99th percentile roughly corresponds to 1 day per season.

This variable can be thought of as the change in the temperature of the warmest day of each season, and changes are provided in probabilistic terms by UKCP09 over land areas.

Find out more


  • A complete list of climate variables for which probabilistic projections are available is given in Table 1.1 of the UKCP09 Climate change projections report. Some additional information about temperature is given in Box 1.2.
  • Information is also available on observed temperature. The UKCP09 Observed Trends report provides details of recent trends in mean, maximum and minimum temperature, as well as days of air frost.