Wispy clouds in a blue sky

User guidance - figure T1

  • The vertical axis of the graph shows values for the variable represented (here, temperature in degrees Celsius). The horizontal axis shows time (here, the overlapping 3-month periods throughout the year). The symbols on the horizontal axis denote the period by the initials of the component months (e.g. JAS = July-August-September).
  • Past observations are shown in two ways:
    • climatology for each year during 1971-2000 (black symbols) - observed temperatures over the reference period for each 3-month period during the year. The 30-year climatological mean is also shown (green circles).
    • values observed in the most recent twelve 3-month periods (coloured line) - to relate the forecast to the most recent past. Fifteen periods are shown to provide a full year's values for the recent past 4.
  • There is a strong seasonal cycle in UK mean temperature, with the broadest range of year-to-year
    variations in winter and early spring.
  • Outlook information shows the prediction for the average over the next 3-month period (here, for temperature) from each of the 42 'members' of the ensemble prediction, after expert modification. Each point represents an equally likely future scenario.