The number of hours of bright sunshine is controlled by the length of day and by cloudiness. The day is shortest in December and longest in June and so in general December is the dullest month and June or July the sunniest.
In general, sunshine duration decreases with increasing altitude, increasing latitude and distance from the coast. Industrial pollution and smoke haze can also reduce sunshine amounts but, since the Clean Air Act of 1956 and a decline in heavy industry, there has been an increase in sunshine duration over the industrial Midlands.
Average annual sunshine durations over the Midlands range from less than 1350 hours in the higher northern and western fringes to about 1500 hours near the southern boundary. These figures compare with values of less than 1100 hours a year in the Shetland Islands to over 1750 hours along the south coast of England and over 1900 hours in the Channel Islands. The tendency for convective cloud to develop over inland areas in summer leads to sunshine averages that are lower than coastal sites.
The graphs show the average monthly sunshine totals for Brize Norton and Shawbury, together with the highest and lowest totals recorded in the stated periods.
The highest known monthly sunshine totals in the region are 314.7 hrs at Brize Norton and 309.6 hours at Ross-On-Wye in July 2006 and 308.5 hours at Cheltenham in June 1957. The highest UK monthly total is 383.9 hours at Eastbourne (East Sussex) in July 1911. In the dullest winter months, less than 20 hours have been recorded - with none at all in December 1890 in central London.
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