The 2015/2016 graph shows the night outside minimum temperature in red and the daily amount of gas used in kWh in blue. The light red and light blue are for the 2014/2015 season. You can see how I've converted my meter readings to kWh here.
It's interesting to plot this graph on a scatter chart to see the direct relationship between minimum night time temperature and gas consumption. The following graph starts frpm November 1st using the regime outlined in 'Announcement' below.
I have alos been experimenting with using 'degree day' tem,perature measurements. Degree day are calculated from a combination of both day time and night time temperatures and can be downloads from a weather station near you. According to degreedays.net (where you can download your local degreeday data), degree days are essentially a simplified representation of outside air-temperature data. They are widely used in the energy industry for calculations relating to the effect of outside air temperature on building energy consumption.
"Heating degree days", or "HDD, which are used below, are a measure of how much (in degrees), and for how long (in days), outside air temperature was lower than a specific "base temperature" (or "balance point"). They are used for calculations relating to the energy consumption required to heat buildings.
You can see that there is quite a tight correlation between gas consumption and degree day tempertaure. This is because I now have the heating on all day downstairs and degree day data is an 'average' of day and night temperatures.