Following reading of an interesting article in 'Weather' the magazine of the Royal Meteorological Society I decided to plot the data by the hour for each month for the total dataset I have since 2008.
I already knew that there is a diurnal variation of the Barometric Pressure across the globe and already have the Diurnal Variations for my location in the Weather Stats. The variations are on a diurnal, semi-diurnal, monthly and annual scale. These variations are influenced by latitude (the variation shows a minimum at the poles and maximum at the equator), by Solar Radiation (more at the equator than the poles obviously), by Gravity (which varies over time), Tidal Influences from the Moon, Atmospheric Gasses, Temperature and Humidity.
Here is the result with the ranges on the right side for each month. Generally speaking the Highest Pressure is during the Summer Months and lower during Winter. I have no idea why November stands out as being significantly lower than the others. There is a ~10mb difference between the top and bottom lines on the graphs.
Just click the graph for a bigger image