Whatever the weather, October is always the month when the full ripeness of late-summer finally turns to decay. The fruit fall, the trees change colour, and British Rail dusts off its book of excuses for leaves on the line. During the 1940s, 1950s and 1960s climatologists became aware of a marked tendency towards warmer and drier Octobers, and indeed a number of Octobers up to 1972 resembled a late-summer month rather than the traditional descent towards winter. This trend was abruptly checked with the exceptionally cold October of 1974 – the coldest since 1905 – and although there were occasional hints of a resumption of the warming process during the next two decades, the recovery has only become convincing since the turn of the century.
On the surface, then, the strong warming in the 1980s and 1990s evinced in most other months of the year appears to be absent in October. A closer look at the weather patterns during the last few decades explains why. The strong mid-century warming was due to an increase in the frequency of southerly winds and a complementary decrease in the frequency of northerlies. Since then the respective frequencies southerly and northerly winds have returned to early-20th century patterns, while temperatures have remained at moderately high levels.
The following table shows the decade by decade changes in temperature, rainfall, sunshine, and thunderstorm frequency since 1890, which enables us to place recent fluctuations in October weather into some sort of historical context.
| Decade | Mean Temperature | Rainfall | Sunshine | Thunderstorms |
| 1890-99 | 8.9°C | 103mm | 92 hours | 0.9 days |
| 1900-09 | 9.9°C | 108mm | 95 hours | 1.0 days |
| 1910-19 | 9.3°C | 94mm | 98 hours | 1.2 days |
| 1920-29 | 10.0°C | 96mm | 116 hours | 0.6 days |
| 1930-39 | 9.7°C | 100mm | 99 hours | 0.8 days |
| 1940-49 | 10.4°C | 90mm | 103 hours | 0.7 days |
| 1950-59 | 10.2°C | 75mm | 98 hours | 0.5 days |
| 1960-69 | 10.9°C | 90mm | 94 hours | 0.5 days |
| 1970-79 | 10.4°C | 67mm | 101 hours | 0.8 days |
| 1980-89 | 10.3°C | 108mm | 107 hours | 0.2 days |
| 1990-99 | 10.4°C | 86mm | 113 hours | 0.6 days |
| 2000-05 | 11.0°C | 133mm | 101 hours | 0.5 days |
The main feature of October temperature, apart from the abnormal warmth of the 1960s, is the step change which appeared to take place between the 1930s and 1940s. The warmest decade during the earlier period was cooler than the coolest in the later period, and the mean temperature between 1890 and 1940 of 9.6C contrasted with 10.4C for 1940-2000. Put another way, that is equivalent to a delay of eight days in the onset of winter.
Changes in October rainfall are less clear cut. The driest decade was the 1970s with a mean rainfall of 67mm, which was immediately followed by the wettest decade in the 1980s with 108mm. although the early years of the new century have been even wetter. If one ignores that blip in the 1980s there was tendency towards less rain in the second half of the twentieth century and three of the driest decades occurred after 1950. Thunderstorm frequency in October has shown a marked decline during the last 100 years.
The blip in the sunshine pattern happened early in the century. The sunniest decade was the 1920s with 116 hours, but that apart there has been a gradual improvement in sunshine hours as the century has progressed, and this brightening up process has been strongly marked in the last 40 years with the average of 94 hours in the 1960s contrasting with 113 hours in the 1990s.
© Philip Eden