Wispy clouds in a blue sky

User guidance - figure T1

Interpretting the vertical and horizontal axis

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).


Interpretting past observations

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.