Spring Sunshine and Smog

Monday 15th Jun 2015 by theWeather Club

Last month, tWC newletter reported that  winter 2014/15 was the sunniest on record; March and April have continued this trend with above average sunshine hours, with 123 hours (21% above the 1981-2010 average) and 212 hours (43% above the 1981-2010 average), respectively.  Indeed, April was sunniest in records dating back to 1929. However, May bucked the trend, with lower sunshine hours and above average rainfall.

During April, parts of the UK also saw some unseasonably warm weather, with temperatures in the low to mid-20s Celsius in the south. Warm air flowed up from the south west and high pressure persisted over the UK for much of the month bringing settled conditions and sunny spells.

However, such weather conditions can often lead to a reduction in air quality across the UK (see p. 10-11 for an air quality science lesson). On 10th April, levels of air pollution were high in many areas of England due to the combination of pollutants trapped near the ground, a light southeasterly air flow which brought additional pollutants from the continent, as well as a small amount of dust that was transported from the Sahara. 

Further afield, Spain experienced exceptional temperatures this spring, exceeding previous records for May. Once verified, the hottest temperature is expected to be around 44oC in Caracaixent, Valencia, which would make it the hottest temperature ever recorded in Europe in May. Such high temperatures would not have been considered exceptional if they had occurred in July or August, however this is twelve degrees above the seasonal norm for May. This heatwave was caused by a hot subtropical air mass that moved up from Morocco, combined with local topographic-induced increases in temperature. It also brought with it a plume of Saharan dust. 

India also sufferend a blitering heatwave during May, with temperatures reaching 48oC. It has so far killed more than 1,100 people and forecasters have warned that the searing temperatures would continue.