Summer & Winter Indexes

[Bottesford]

As devised by Mr Data, here's how the summer and winter indexes are calculated:

Summer index = 10 x [(mean max of summer) +(total sunshine/67) - (rain days/ ]

Winter index = 10 x [(number of air frosts + number of days of falling sleet/snow + number of days of lying snow at 9am)/ mean winter maximum]