Mean annual temperatures over the region vary from around 8 °C to just over 10 °C. The highest values occur in the lower Severn valley, whilst the lowest occur at the higher altitudes such as the Peak District. Over the UK, mean annual temperatures range from about 7 °C in the Shetlands to over 11 °C in Cornwall and the Channel Islands.
Temperature shows both a seasonal and a diurnal variation. Minimum temperatures usually occur around sunrise and maximum temperatures are normally 2 or 3 hours after midday. Since the Midlands region is at some distance from the sea, with its moderating effects on temperature, the annual range is more pronounced than in most parts of the UK. Sharp winter frosts are common and there are occasional very hot summer days, particularly in the south and east of the region. These temperature extremes of both winter and summer are a key characteristic of the Midlands climate.
January is the coldest month, with mean daily minimum temperatures varying from just below 0 °C to about 1.5 °C. The higher values occur in the lower Severn valley and are due to the incursion of milder maritime air via the Bristol Channel. Cold air drainage into the river valleys results in large-scale frost hollows, with the Severn, Wye and Avon valleys enhancing the general frostiness of the western half of the Midlands. With snow cover, some remarkably low temperatures have been recorded, such as -25.2 °C at Shawbury, Shropshire on 13 December 1981 and -26.1 °C at Newport, Shropshire on 10 January 1982. This value at Newport is the lowest ever recorded in England.
July is the warmest month, with mean daily maximum temperatures approaching 22 °C in the south and east Midlands. The highest July mean daily maxima occur in the London area (22.5 °C) whilst the lowest occur in the Shetlands (15 °C). Extreme maximum temperatures can occur in July or August. For example, on 3 July 1976 35.9 °C was recorded at Cheltenham and on 9 August 1911 36.7 °C occurred at Raunds, Northamptonshire. On 3 August 1990, temperatures exceeded 34 °C widely over the Midlands, with 37.1 °C at Cheltenham, a new national record. This stood until the heat wave of August 2003, when 38.5 °C was measured at Faversham, Kent.
The variation of mean daily maximum and minimum temperatures month by month, together with the highest and lowest temperatures recorded, is shown for Brize Norton (Oxfordshire) and Keele (Staffordshire). These graphs reflect the similarity in mean temperatures across the region, with only a gradual south to north gradient. However, extreme minima are dictated more by local topography.
Frost is a widespread, occasionally marked, characteristic of the Midlands. An 'air frost' occurs when the temperature at 1.25 metres above the ground falls below 0 °C, whereas incidence of a 'ground frost' refers to a temperature below 0 °C measured on a grass surface. The average number of days with air frost in the Midlands varies from about 40 a year in the lower Severn valley to over 65 a year in the Peak District and sheltered areas of the Welsh Marches. Ground frost occurs on average on about 100 to 125 days per year, with a similar distribution to air frost.
The graphs show the average frequency of air and ground frost at Brize Norton and Keele. These show that, although the summer months are usually free of air frost, ground frost may occur at any time of the year, especially at sites in valleys.
