The month of December in London experiences essentially constant cloud cover, with the percentage of time that the sky is overcast or mostly cloudy remaining about 72% throughout the month. The highest chance of overcast or mostly cloudy conditions is 74% on December 27.
A wet day is one with at least 0.04 inches of liquid or liquid-equivalent precipitation. In London, the chance of a wet day over the course of December is gradually increasing, starting the month at 29% and ending it at 32%.
The average sliding 31-day rainfall during December in London is essentially constant, remaining about 2.0 inches throughout, and rarely exceeding 3.5 inches or falling below 0.6 inches.
Over the course of December in London, the length of the day is gradually decreasing. From the start to the end of the month, the length of the day decreases by 17 minutes, implying an average daily decrease of 33 seconds, and weekly decrease of 3 minutes, 53 seconds.
The horizontal axis is the day, the vertical axis is the hour of the day, and the colored areas indicate when the moon is above the horizon. The vertical gray bars (new Moons) and blue bars (full Moons) indicate key Moon phases.
We base the humidity comfort level on the dew point, as it determines whether perspiration will evaporate from the skin, thereby cooling the body. Lower dew points feel drier and higher dew points feel more humid.
The average hourly wind speed in London is increasing during December, increasing from 11.9 miles per hour to 13.1 miles per hour over the course of the month.