Change in Daily Temperature Cycle UK

An interesting observation from the last couple of weeks in the UK shows how the daily air temperature cycle has changed. Up until the 21st of September there had been a clear daily cycle. The peak temperature had been much higher than the low temperature.

From the evening of the 21st of September, the daily cycle has changed. The peaks and lows of each day are much closer. On some days the daily cycle can still be seen but is less obvious.

If we overlay the wind speed data onto the air temperature, a trend can be seen. Mostly the average wind speed per day has increased since the change in daily temperature cycle. Perhaps this wind is bringing cooler air to the area?

There could be multiple explanations for this cycle change but one thing is for sure, Autumn has now arrived!