May was a wet and cool month, as the majority of the UK received above average rainfall and average daily maximum temperatures provisionally ranked as the coldest May since 1996.
Total outflows from the UK were high in early May, reflecting the spatial coherence of high flows, and in recession thereafter. Soil moisture deficits (SMDs) declined in many northern and western areas and end of May soils were the wettest on record (in a series from 1961) for North West Britain. Despite this, groundwater levels fell during May as normal, and the area of low or notably low levels in the southern Chalk expanded slightly. Overall reservoir stocks for England & Wales increased and were near average, and the water resource outlook is healthy at the beginning of summer.
Further details can be found here.